harmony 鸿蒙OffscreenCanvasRenderingContext2D
OffscreenCanvasRenderingContext2D
Use OffscreenCanvasRenderingContext2D to draw rectangles, images, and text offscreen onto a canvas. Drawing offscreen onto a canvas is a process where content to draw onto the canvas is first drawn in the buffer, and then converted into a picture, and finally the picture is drawn on the canvas. This process increases the drawing efficiency.
NOTE
The APIs of this module are supported since API version 8. Updates will be marked with a superscript to indicate their earliest API version.
APIs
OffscreenCanvasRenderingContext2D(width: number, height: number, settings?: RenderingContextSettings)
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Description |
|---|---|---|---|
| width | number | Yes | Width of the offscreen canvas. |
| height | number | Yes | Height of the offscreen canvas. |
| settings | RenderingContextSettings | No | See RenderingContextSettings. |
Attributes
| Name | Type | Description |
|---|---|---|
| fillStyle | string |number10+ |CanvasGradient |CanvasPattern | Style to fill an area. - When the type is string, this attribute indicates the color of the filling area. - When the type is number, this attribute indicates the color of the filling area. - When the type is CanvasGradient, this attribute indicates a gradient object, which is created using the createLinearGradient API. - When the type is CanvasPattern, this attribute indicates a pattern, which is created using the createPattern API. Since API version 9, this API is supported in ArkTS widgets. |
| lineWidth | number | Line width. Since API version 9, this API is supported in ArkTS widgets. |
| strokeStyle | string |number10+ |CanvasGradient |CanvasPattern | Stroke style. - When the type is string, this attribute indicates the stroke color. - When the type is number, this attribute indicates the stroke color. - When the type is CanvasGradient, this attribute indicates a gradient object, which is created using the createLinearGradient API. - When the type is CanvasPattern, this attribute indicates a pattern, which is created using the createPattern API. Since API version 9, this API is supported in ArkTS widgets. |
| lineCap | CanvasLineCap | Style of the line endpoints. The options are as follows: - butt: The endpoints of the line are squared off. - round: The endpoints of the line are rounded. - square: The endpoints of the line are squared off, and each endpoint has added a rectangle whose length is the same as the line thickness and whose width is half of the line thickness. - Default value: ‘butt’ Since API version 9, this API is supported in ArkTS widgets. |
| lineJoin | CanvasLineJoin | Style of the shape used to join line segments. The options are as follows: - round: The intersection is a sector, whose radius at the rounded corner is equal to the line width. - bevel: The intersection is a triangle. The rectangular corner of each line is independent. - miter: The intersection has a miter corner by extending the outside edges of the lines until they meet. You can view the effect of this attribute in miterLimit. - Default value: ‘miter’ Since API version 9, this API is supported in ArkTS widgets. |
| miterLimit | number | Maximum miter length. The miter length is the distance between the inner corner and the outer corner where two lines meet. - Default value: 10 Since API version 9, this API is supported in ArkTS widgets. |
| font | string | Font style. Syntax: ctx.font=‘font-size font-family’ - (Optional) font-size: font size and line height. The unit can only be pixels. (Optional) font-family: font family. Syntax: ctx.font=‘font-style font-weight font-size font-family’ - (Optional) font-style: font style. Available values are normal and italic. - (Optional) font-weight: font weight. Available values are as follows: normal, bold, bolder, lighter, 100, 200, 300, 400, 500, 600, 700, 800, 900. - (Optional) font-size: font size and line height. The unit can be px or vp and must be specified. - (Optional) font-family: font family. Available values are sans-serif, serif, and monospace. Default value: ‘normal normal 14px sans-serif’ Since API version 9, this API is supported in ArkTS widgets. |
| textAlign | CanvasTextAlign | Text alignment mode. Available values are as follows: - left: The text is left-aligned. - right: The text is right-aligned. - center: The text is center-aligned. - start: The text is aligned with the start bound. - end: The text is aligned with the end bound. NOTE In the ltr layout mode, the value ‘start’ equals ‘left’. In the rtl layout mode, the value ‘start’ equals ‘right’. - Default value: ‘left’ Since API version 9, this API is supported in ArkTS widgets. |
| textBaseline | CanvasTextBaseline | Horizontal alignment mode of text. Available values are as follows: - alphabetic: The text baseline is the normal alphabetic baseline. - top: The text baseline is on the top of the text bounding box. - hanging: The text baseline is a hanging baseline over the text. - middle: The text baseline is in the middle of the text bounding box. ‘ideographic’: The text baseline is the ideographic baseline. If a character exceeds the alphabetic baseline, the ideographic baseline is located at the bottom of the excess character. - bottom: The text baseline is at the bottom of the text bounding box. Its difference from the ideographic baseline is that the ideographic baseline does not consider letters in the next line. - Default value: ‘alphabetic’ Since API version 9, this API is supported in ArkTS widgets. |
| globalAlpha | number | Opacity. 0.0: completely transparent. 1.0: completely opaque. |
| lineDashOffset | number | Offset of the dashed line. The precision is float. - Default value: 0.0 Since API version 9, this API is supported in ArkTS widgets. |
| globalCompositeOperation | string | Composition operation type. Available values are as follows: ‘source-over’, ‘source-atop’, ‘source-in’, ‘source-out’, ‘destination-over’, ‘destination-atop’, ‘destination-in’, ‘destination-out’, ‘lighter’, ‘copy’, and ‘xor’. - Default value: ‘source-over’ Since API version 9, this API is supported in ArkTS widgets. |
| shadowBlur | number | Blur level during shadow drawing. A larger value indicates a more blurred effect. The precision is float. - Default value: 0.0 Since API version 9, this API is supported in ArkTS widgets. |
| shadowColor | string | Shadow color. Since API version 9, this API is supported in ArkTS widgets. |
| shadowOffsetX | number | X-axis shadow offset relative to the original object. Since API version 9, this API is supported in ArkTS widgets. |
| shadowOffsetY | number | Y-axis shadow offset relative to the original object. Since API version 9, this API is supported in ArkTS widgets. |
| imageSmoothingEnabled | boolean | Whether to adjust the image smoothness during image drawing. The value true means to enable this feature, and false means the opposite. - Default value: true Since API version 9, this API is supported in ArkTS widgets. |
| imageSmoothingQuality | ImageSmoothingQuality | Quality of image smoothing. This attribute works only when imageSmoothingEnabled is set to true. Available values are as follows: - ‘low’: low quality. - ‘medium’: medium quality. - ‘high’: high quality. Default value: ‘low’ Since API version 9, this API is supported in ArkTS widgets. |
| direction | CanvasDirection | Text direction used for drawing text. Available values are as follows: - ‘inherit’: The text direction is inherited from the <Canvas> component. - ‘ltr’: The text direction is from left to right. - ‘rtl’: The text direction is from right to left. Default value: ‘inherit’ Since API version 9, this API is supported in ArkTS widgets. |
| filter | string | Filter effect. Available values are as follows: - ‘none’: no filter effect. - ‘blur’: applies the Gaussian blur for the image. - ‘brightness’: applies a linear multiplication to the image to make it look brighter or darker. - ‘contrast’: adjusts the image contrast. - ‘grayscale’: converts the image to a grayscale image. - ‘hue-rotate’: applies hue rotation to the image. - ‘invert’: inverts the input image. - ‘opacity’: sets the opacity of the image. - ‘saturate’: sets the saturation of the image. - ‘sepia’: converts the image to dark brown. Default value: ‘none’ Since API version 9, this API is supported in ArkTS widgets. |
NOTE For fillStyle, shadowColor, and strokeStyle, the value format of the string type is ‘rgb(255, 255, 255)’, ‘rgba(255, 255, 255, 1.0)’, ‘#FFFFFF’.
fillStyle
// xxx.ets
@Entry
@Component
struct FillStyleExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillStyle = '#0000ff'
offContext.fillRect(20, 20, 150, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
// xxx.ets
@Entry
@Component
struct FillStyleExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillStyle = 0x0000FF
offContext.fillRect(20, 20, 150, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
lineWidth
// xxx.ets
@Entry
@Component
struct LineWidthExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.lineWidth = 5
offContext.strokeRect(25, 25, 85, 105)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
strokeStyle
// xxx.ets
@Entry
@Component
struct StrokeStyleExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.lineWidth = 10
offContext.strokeStyle = '#0000ff'
offContext.strokeRect(25, 25, 155, 105)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
// xxx.ets
@Entry
@Component
struct StrokeStyleExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.lineWidth = 10
offContext.strokeStyle = 0x0000ff
offContext.strokeRect(25, 25, 155, 105)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
lineCap
// xxx.ets
@Entry
@Component
struct LineCapExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.lineWidth = 8
offContext.beginPath()
offContext.lineCap = 'round'
offContext.moveTo(30, 50)
offContext.lineTo(220, 50)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
lineJoin
// xxx.ets
@Entry
@Component
struct LineJoinExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.lineWidth = 8
offContext.lineJoin = 'miter'
offContext.moveTo(30, 30)
offContext.lineTo(120, 60)
offContext.lineTo(30, 110)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
miterLimit
// xxx.ets
@Entry
@Component
struct MiterLimit {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.lineWidth = 8
offContext.lineJoin = 'miter'
offContext.miterLimit = 3
offContext.moveTo(30, 30)
offContext.lineTo(60, 35)
offContext.lineTo(30, 37)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
font
// xxx.ets
@Entry
@Component
struct Fonts {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.font = '30px sans-serif'
offContext.fillText("Hello World", 20, 60)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
textAlign
// xxx.ets
@Entry
@Component
struct CanvasExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.strokeStyle = '#0000ff'
offContext.moveTo(140, 10)
offContext.lineTo(140, 160)
offContext.stroke()
offContext.font = '18px sans-serif'
offContext.textAlign = 'start'
offContext.fillText('textAlign=start', 140, 60)
offContext.textAlign = 'end'
offContext.fillText('textAlign=end', 140, 80)
offContext.textAlign = 'left'
offContext.fillText('textAlign=left', 140, 100)
offContext.textAlign = 'center'
offContext.fillText('textAlign=center',140, 120)
offContext.textAlign = 'right'
offContext.fillText('textAlign=right',140, 140)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
textBaseline
// xxx.ets
@Entry
@Component
struct TextBaseline {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.strokeStyle = '#0000ff'
offContext.moveTo(0, 120)
offContext.lineTo(400, 120)
offContext.stroke()
offContext.font = '20px sans-serif'
offContext.textBaseline = 'top'
offContext.fillText('Top', 10, 120)
offContext.textBaseline = 'bottom'
offContext.fillText('Bottom', 55, 120)
offContext.textBaseline = 'middle'
offContext.fillText('Middle', 125, 120)
offContext.textBaseline = 'alphabetic'
offContext.fillText('Alphabetic', 195, 120)
offContext.textBaseline = 'hanging'
offContext.fillText('Hanging', 295, 120)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
globalAlpha
// xxx.ets
@Entry
@Component
struct GlobalAlpha {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillStyle = 'rgb(0,0,255)'
offContext.fillRect(0, 0, 50, 50)
offContext.globalAlpha = 0.4
offContext.fillStyle = 'rgb(0,0,255)'
offContext.fillRect(50, 50, 50, 50)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
lineDashOffset
// xxx.ets
@Entry
@Component
struct LineDashOffset {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.arc(100, 75, 50, 0, 6.28)
offContext.setLineDash([10,20])
offContext.lineDashOffset = 10.0
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
globalCompositeOperation
| Name | Description |
|---|---|
| source-over | Displays the new drawing above the existing drawing. This attribute is used by default. |
| source-atop | Displays the new drawing on the top of the existing drawing. |
| source-in | Displays the new drawing inside the existing drawing. |
| source-out | Displays part of the new drawing that is outside of the existing drawing. |
| destination-over | Displays the existing drawing above the new drawing. |
| destination-atop | Displays the existing drawing on the top of the new drawing. |
| destination-in | Displays the existing drawing inside the new drawing. |
| destination-out | Displays the existing drawing outside the new drawing. |
| lighter | Displays both the new and existing drawing. |
| copy | Displays the new drawing and neglects the existing drawing. |
| xor | Combines the new drawing and existing drawing using the XOR operation. |
// xxx.ets
@Entry
@Component
struct GlobalCompositeOperation {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillStyle = 'rgb(255,0,0)'
offContext.fillRect(20, 20, 50, 50)
offContext.globalCompositeOperation = 'source-over'
offContext.fillStyle = 'rgb(0,0,255)'
offContext.fillRect(50, 50, 50, 50)
offContext.fillStyle = 'rgb(255,0,0)'
offContext.fillRect(120, 20, 50, 50)
offContext.globalCompositeOperation = 'destination-over'
offContext.fillStyle = 'rgb(0,0,255)'
offContext.fillRect(150, 50, 50, 50)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
shadowBlur
// xxx.ets
@Entry
@Component
struct ShadowBlur {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.shadowBlur = 30
offContext.shadowColor = 'rgb(0,0,0)'
offContext.fillStyle = 'rgb(255,0,0)'
offContext.fillRect(20, 20, 100, 80)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
shadowColor
// xxx.ets
@Entry
@Component
struct ShadowColor {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.shadowBlur = 30
offContext.shadowColor = 'rgb(0,0,255)'
offContext.fillStyle = 'rgb(255,0,0)'
offContext.fillRect(30, 30, 100, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
shadowOffsetX
// xxx.ets
@Entry
@Component
struct ShadowOffsetX {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.shadowBlur = 10
offContext.shadowOffsetX = 20
offContext.shadowColor = 'rgb(0,0,0)'
offContext.fillStyle = 'rgb(255,0,0)'
offContext.fillRect(20, 20, 100, 80)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
shadowOffsetY
// xxx.ets
@Entry
@Component
struct ShadowOffsetY {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.shadowBlur = 10
offContext.shadowOffsetY = 20
offContext.shadowColor = 'rgb(0,0,0)'
offContext.fillStyle = 'rgb(255,0,0)'
offContext.fillRect(30, 30, 100, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
imageSmoothingEnabled
// xxx.ets
@Entry
@Component
struct ImageSmoothingEnabled {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private img:ImageBitmap = new ImageBitmap("common/images/icon.jpg")
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.imageSmoothingEnabled = false
offContext.drawImage(this.img,0,0,400,200)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
Methods
fillRect
fillRect(x: number, y: number, w: number, h: number): void
Fills a rectangle on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-coordinate of the upper left corner of the rectangle. |
| y | number | Yes | 0 | Y-coordinate of the upper left corner of the rectangle. |
| width | number | Yes | 0 | Width of the rectangle. |
| height | number | Yes | 0 | Height of the rectangle. |
Example
// xxx.ets
@Entry
@Component
struct FillRect {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillRect(30,30,100,100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
strokeRect
strokeRect(x: number, y: number, w: number, h: number): void
Draws an outlined rectangle on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-coordinate of the upper left corner of the rectangle. |
| y | number | Yes | 0 | Y-coordinate of the upper left corner of the rectangle. |
| width | number | Yes | 0 | Width of the rectangle. |
| height | number | Yes | 0 | Height of the rectangle. |
Example
// xxx.ets
@Entry
@Component
struct StrokeRect {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.strokeRect(30, 30, 200, 150)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
clearRect
clearRect(x: number, y: number, w: number, h: number): void
Clears the content in a rectangle on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-coordinate of the upper left corner of the rectangle. |
| y | number | Yes | 0 | Y-coordinate of the upper left corner of the rectangle. |
| width | number | Yes | 0 | Width of the rectangle. |
| height | number | Yes | 0 | Height of the rectangle. |
Example
// xxx.ets
@Entry
@Component
struct ClearRect {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillStyle = 'rgb(0,0,255)'
offContext.fillRect(20,20,200,200)
offContext.clearRect(30,30,150,100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
fillText
fillText(text: string, x: number, y: number, maxWidth?: number): void
Draws filled text on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| text | string | Yes | ”” | Text to draw. |
| x | number | Yes | 0 | X-coordinate of the lower left corner of the text. |
| y | number | Yes | 0 | Y-coordinate of the lower left corner of the text. |
| maxWidth | number | No | - | Maximum width allowed for the text. |
Example
// xxx.ets
@Entry
@Component
struct FillText {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.font = '30px sans-serif'
offContext.fillText("Hello World!", 20, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
strokeText
strokeText(text: string, x: number, y: number): void
Draws a text stroke on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| text | string | Yes | ”” | Text to draw. |
| x | number | Yes | 0 | X-coordinate of the lower left corner of the text. |
| y | number | Yes | 0 | Y-coordinate of the lower left corner of the text. |
| maxWidth | number | No | - | Maximum width of the text to be drawn. |
Example
// xxx.ets
@Entry
@Component
struct StrokeText {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.font = '55px sans-serif'
offContext.strokeText("Hello World!", 20, 60)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
measureText
measureText(text: string): TextMetrics
Returns a TextMetrics object used to obtain the width of specified text.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| text | string | Yes | ”” | Text to be measured. |
Return value
| Type | Description |
|---|---|
| TextMetrics | TextMetrics object. Since API version 9, this API is supported in ArkTS widgets. |
TextMetrics attributes
| Name | Type | Description |
|---|---|---|
| width | number | Width of the text. |
| height | number | Height of the text. |
| actualBoundingBoxAscent | number | Distance from the horizontal line specified by the CanvasRenderingContext2D.textBaseline attribute to the top of the bounding rectangle used to render the text. The current value is 0. |
| actualBoundingBoxDescent | number | Distance from the horizontal line specified by the CanvasRenderingContext2D.textBaseline attribute to the bottom of the bounding rectangle used to render the text. The current value is 0. |
| actualBoundingBoxLeft | number | Distance parallel to the baseline from the alignment point determined by the CanvasRenderingContext2D.textAlign attribute to the left side of the bounding rectangle of the text. The current value is 0. |
| actualBoundingBoxRight | number | Distance parallel to the baseline from the alignment point determined by the CanvasRenderingContext2D.textAlign attribute to the right side of the bounding rectangle of the text. The current value is 0. |
| alphabeticBaseline | number | Distance from the horizontal line specified by the CanvasRenderingContext2D.textBaseline attribute to the alphabetic baseline of the line box. The current value is 0. |
| emHeightAscent | number | Distance from the horizontal line specified by the CanvasRenderingContext2D.textBaseline attribute to the top of the em square in the line box. The current value is 0. |
| emHeightDescent | number | Distance from the horizontal line specified by the CanvasRenderingContext2D.textBaseline attribute to the bottom of the em square in the line box. The current value is 0. |
| fontBoundingBoxAscent | number | Distance from the horizontal line specified by the CanvasRenderingContext2D.textBaseline attribute to the top of the highest bounding rectangle of all the fonts used to render the text. The current value is 0. |
| fontBoundingBoxDescent | number | Distance from the horizontal line specified by the CanvasRenderingContext2D.textBaseline attribute to the bottom of the bounding rectangle of all the fonts used to render the text. The current value is 0. |
| hangingBaseline | number | Distance from the horizontal line specified by the CanvasRenderingContext2D.textBaseline attribute to the hanging baseline of the line box. The current value is 0. |
| ideographicBaseline | number | Distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the ideographic baseline of the line box. The current value is 0. |
Example
// xxx.ets
@Entry
@Component
struct MeasureText {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.font = '50px sans-serif'
offContext.fillText("Hello World!", 20, 100)
offContext.fillText("width:" + this.context.measureText("Hello World!").width, 20, 200)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
stroke
stroke(path?: Path2D): void
Strokes a path.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| path | Path2D | No | null | A Path2D path to draw. |
Example
// xxx.ets
@Entry
@Component
struct Stroke {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.moveTo(25, 25)
offContext.lineTo(25, 105)
offContext.lineTo(75, 105)
offContext.lineTo(75, 25)
offContext.strokeStyle = 'rgb(0,0,255)'
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
beginPath
beginPath(): void
Creates a drawing path.
Since API version 9, this API is supported in ArkTS widgets.
Example
// xxx.ets
@Entry
@Component
struct BeginPath {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.lineWidth = 6
offContext.strokeStyle = '#0000ff'
offContext.moveTo(15, 80)
offContext.lineTo(280, 160)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
moveTo
moveTo(x: number, y: number): void
Moves a drawing path to a target position on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-coordinate of the target position. |
| y | number | Yes | 0 | Y-coordinate of the target position. |
Example
// xxx.ets
@Entry
@Component
struct MoveTo {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.moveTo(10, 10)
offContext.lineTo(280, 160)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
lineTo
lineTo(x: number, y: number): void
Connects the current point to a target position using a straight line.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-coordinate of the target position. |
| y | number | Yes | 0 | Y-coordinate of the target position. |
Example
// xxx.ets
@Entry
@Component
struct LineTo {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.moveTo(10, 10)
offContext.lineTo(280, 160)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
closePath
closePath(): void
Draws a closed path.
Since API version 9, this API is supported in ArkTS widgets.
Example
// xxx.ets
@Entry
@Component
struct ClosePath {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.moveTo(30, 30)
offContext.lineTo(110, 30)
offContext.lineTo(70, 90)
offContext.closePath()
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
createPattern
createPattern(image: ImageBitmap, repetition: string|null): CanvasPattern|null
Creates a pattern for image filling based on a specified source image and repetition mode.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| image | ImageBitmap | Yes | null | Source image. For details, see ImageBitmap. |
| repetition | string | Yes | ”” | Repetition mode. The value can be ‘repeat’, ‘repeat-x’, ‘repeat-y’, ‘no-repeat’, ‘clamp’, or ‘mirror’. |
Return value
| Type | Description |
|---|---|
| CanvasPattern | Created pattern for image filling based on a specified source image and repetition mode. |
Example
// xxx.ets
@Entry
@Component
struct CreatePattern {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private img:ImageBitmap = new ImageBitmap("common/images/icon.jpg")
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let pattern = offContext.createPattern(this.img, 'repeat')
offContext.fillStyle = pattern as CanvasPattern
offContext.fillRect(0, 0, 200, 200)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
bezierCurveTo
bezierCurveTo(cp1x: number, cp1y: number, cp2x: number, cp2y: number, x: number, y: number): void
Draws a cubic bezier curve on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| cp1x | number | Yes | 0 | X-coordinate of the first parameter of the bezier curve. |
| cp1y | number | Yes | 0 | Y-coordinate of the first parameter of the bezier curve. |
| cp2x | number | Yes | 0 | X-coordinate of the second parameter of the bezier curve. |
| cp2y | number | Yes | 0 | Y-coordinate of the second parameter of the bezier curve. |
| x | number | Yes | 0 | X-coordinate of the end point on the bezier curve. |
| y | number | Yes | 0 | Y-coordinate of the end point on the bezier curve. |
Example
// xxx.ets
@Entry
@Component
struct BezierCurveTo {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.moveTo(10, 10)
offContext.bezierCurveTo(20, 100, 200, 100, 200, 20)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
quadraticCurveTo
quadraticCurveTo(cpx: number, cpy: number, x: number, y: number): void
Draws a quadratic curve on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| cpx | number | Yes | 0 | X-coordinate of the bezier curve parameter. |
| cpy | number | Yes | 0 | Y-coordinate of the bezier curve parameter. |
| x | number | Yes | 0 | X-coordinate of the end point on the bezier curve. |
| y | number | Yes | 0 | Y-coordinate of the end point on the bezier curve. |
Example
// xxx.ets
@Entry
@Component
struct QuadraticCurveTo {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.moveTo(20, 20)
offContext.quadraticCurveTo(100, 100, 200, 20)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
arc
arc(x: number, y: number, radius: number, startAngle: number, endAngle: number, counterclockwise?: boolean): void
Draws an arc on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-coordinate of the center point of the arc. |
| y | number | Yes | 0 | Y-coordinate of the center point of the arc. |
| radius | number | Yes | 0 | Radius of the arc. |
| startAngle | number | Yes | 0 | Start radian of the arc. |
| endAngle | number | Yes | 0 | End radian of the arc. |
| counterclockwise | boolean | No | false | Whether to draw the arc counterclockwise. |
Example
// xxx.ets
@Entry
@Component
struct Arc {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.arc(100, 75, 50, 0, 6.28)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
arcTo
arcTo(x1: number, y1: number, x2: number, y2: number, radius: number): void
Draws an arc based on the radius and points on the arc.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x1 | number | Yes | 0 | X-coordinate of the first point on the arc. |
| y1 | number | Yes | 0 | Y-coordinate of the first point on the arc. |
| x2 | number | Yes | 0 | X-coordinate of the second point on the arc. |
| y2 | number | Yes | 0 | Y-coordinate of the second point on the arc. |
| radius | number | Yes | 0 | Radius of the arc. |
Example
// xxx.ets
@Entry
@Component
struct ArcTo {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.moveTo(100, 20)
offContext.arcTo(150, 20, 150, 70, 50)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
ellipse
ellipse(x: number, y: number, radiusX: number, radiusY: number, rotation: number, startAngle: number, endAngle: number, counterclockwise?: boolean): void
Draws an ellipse in the specified rectangular region on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-coordinate of the ellipse center. |
| y | number | Yes | 0 | Y-coordinate of the ellipse center. |
| radiusX | number | Yes | 0 | Ellipse radius on the x-axis. |
| radiusY | number | Yes | 0 | Ellipse radius on the y-axis. |
| rotation | number | Yes | 0 | Rotation angle of the ellipse. The unit is radian. |
| startAngle | number | Yes | 0 | Angle of the start point for drawing the ellipse. The unit is radian. |
| endAngle | number | Yes | 0 | Angle of the end point for drawing the ellipse. The unit is radian. |
| counterclockwise | boolean | No | false | Whether to draw the ellipse counterclockwise. true: Draw the ellipse counterclockwise. false: Draw the ellipse clockwise. |
Example
// xxx.ets
@Entry
@Component
struct CanvasExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.beginPath()
offContext.ellipse(200, 200, 50, 100, Math.PI * 0.25, Math.PI * 0.5, Math.PI * 2)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
rect
rect(x: number, y: number, w: number, h: number): void
Creates a rectangle on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-coordinate of the upper left corner of the rectangle. |
| y | number | Yes | 0 | Y-coordinate of the upper left corner of the rectangle. |
| w | number | Yes | 0 | Width of the rectangle. |
| h | number | Yes | 0 | Height of the rectangle. |
Example
// xxx.ets
@Entry
@Component
struct CanvasExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.rect(20, 20, 100, 100) // Create a 100*100 rectangle at (20, 20)
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
fill
fill(fillRule?: CanvasFillRule): void
Fills the area inside a closed path on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| fillRule | CanvasFillRule | No | “nonzero” | Rule by which to determine whether a point is inside or outside the area to fill. The options are “nonzero” and “evenodd”. |
// xxx.ets
@Entry
@Component
struct Fill {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillStyle = '#000000'
offContext.rect(20, 20, 100, 100) // Create a 100*100 rectangle at (20, 20)
offContext.fill()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
fill(path: Path2D, fillRule?: CanvasFillRule): void
Fills the area inside a closed path on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| path | Path2D | Yes | A Path2D path to fill. | |
| fillRule | CanvasFillRule | No | “nonzero” | Rule by which to determine whether a point is inside or outside the area to fill. The options are “nonzero” and “evenodd”. |
Example
// xxx.ets
@Entry
@Component
struct Fill {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let region = new Path2D()
region.moveTo(30, 90)
region.lineTo(110, 20)
region.lineTo(240, 130)
region.lineTo(60, 130)
region.lineTo(190, 20)
region.lineTo(270, 90)
region.closePath()
// Fill path
offContext.fillStyle = '#00ff00'
offContext.fill(region, "evenodd")
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
clip
clip(fillRule?: CanvasFillRule): void
Sets the current path to a clipping path.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| fillRule | CanvasFillRule | No | “nonzero” | Rule by which to determine whether a point is inside or outside the area to clip. The options are “nonzero” and “evenodd”. |
Example
// xxx.ets
@Entry
@Component
struct Clip {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.rect(0, 0, 100, 200)
offContext.stroke()
offContext.clip()
offContext.fillStyle = "rgb(255,0,0)"
offContext.fillRect(0, 0, 200, 200)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
clip(path:Path2D, fillRule?: CanvasFillRule): void
Sets a closed path to a clipping path.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| path | Path2D | Yes | A Path2D path to clip. | |
| fillRule | CanvasFillRule | No | “nonzero” | Rule by which to determine whether a point is inside or outside the area to clip. The options are “nonzero” and “evenodd”. |
Example
// xxx.ets
@Entry
@Component
struct Clip {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let region = new Path2D()
region.moveTo(30, 90)
region.lineTo(110, 20)
region.lineTo(240, 130)
region.lineTo(60, 130)
region.lineTo(190, 20)
region.lineTo(270, 90)
region.closePath()
offContext.clip(region,"evenodd")
offContext.fillStyle = "rgb(0,255,0)"
offContext.fillRect(0, 0, 600, 600)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
filter
filter(filter: string): void
Sets a filter for the image on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| filter | string | Yes | - | Functions that accept various filter effects. Available values are as follows: - ‘none’: no filter effect. - ‘blur’: applies the Gaussian blur for the image. - ‘brightness’: applies a linear multiplication to the image to make it look brighter or darker. - ‘contrast’: adjusts the image contrast. - ‘grayscale’: converts the image to a grayscale image. - ‘hue-rotate’: applies hue rotation to the image. - ‘invert’: inverts the input image. - ‘opacity’: sets the opacity of the image. - ‘saturate’: sets the saturation of the image. - ‘sepia’: converts the image to dark brown. Default value: ‘none’ |
Example
// xxx.ets
@Entry
@Component
struct FilterDemoOff {
private settings: RenderingContextSettings = new RenderingContextSettings(true);
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings);
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
private img:ImageBitmap = new ImageBitmap("common/images/example.jpg");
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let offctx = offContext
let img = this.img
offctx.drawImage(img, 0, 0, 100, 100);
offctx.filter = 'grayscale(50%)';
offctx.drawImage(img, 100, 0, 100, 100);
offctx.filter = 'sepia(60%)';
offctx.drawImage(img, 200, 0, 100, 100);
offctx.filter = 'saturate(30%)';
offctx.drawImage(img, 0, 100, 100, 100);
offctx.filter = 'hue-rotate(90degree)';
offctx.drawImage(img, 100, 100, 100, 100);
offctx.filter = 'invert(100%)';
offctx.drawImage(img, 200, 100, 100, 100);
offctx.filter = 'opacity(25%)';
offctx.drawImage(img, 0, 200, 100, 100);
offctx.filter = 'brightness(0.4)';
offctx.drawImage(img, 100, 200, 100, 100);
offctx.filter = 'contrast(200%)';
offctx.drawImage(img, 200, 200, 100, 100);
offctx.filter = 'blur(5px)';
offctx.drawImage(img, 0, 300, 100, 100);
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
resetTransform
resetTransform(): void
Resets the current transform to the identity matrix. This API is a void API.
Since API version 9, this API is supported in ArkTS widgets.
direction
direction(direction: CanvasDirection): void
Sets the text direction for drawing text.
Since API version 9, this API is supported in ArkTS widgets.
Example
// xxx.ets
@Entry
@Component
struct DirectionDemoOff {
private settings: RenderingContextSettings = new RenderingContextSettings(true);
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings);
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let offctx = offContext
offctx.font = '48px serif';
offctx.textAlign = 'start'
offctx.fillText("Hi ltr!", 200, 50);
offctx.direction = "rtl";
offctx.fillText("Hi rtl!", 200, 100);
let image = offctx.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
rotate
rotate(angle: number): void
Rotates a canvas clockwise around its coordinate axes.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| angle | number | Yes | 0 | Clockwise rotation angle. You can use Math.PI / 180 to convert the angle to a radian. |
Example
// xxx.ets
@Entry
@Component
struct Rotate {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.rotate(45 * Math.PI / 180)
offContext.fillRect(70, 20, 50, 50)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
scale
scale(x: number, y: number): void
Scales the canvas based on scale factors.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | Horizontal scale factor. |
| y | number | Yes | 0 | Vertical scale factor. |
Example
// xxx.ets
@Entry
@Component
struct Scale {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.lineWidth = 3
offContext.strokeRect(30, 30, 50, 50)
offContext.scale(2, 2) // Scale to 200%
offContext.strokeRect(30, 30, 50, 50)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
transform
transform(a: number, b: number, c: number, d: number, e: number, f: number): void
Defines a transformation matrix. To transform a graph, you only need to set parameters of the matrix. The coordinates of the graph are multiplied by the matrix values to obtain new coordinates of the transformed graph. You can use the matrix to implement multiple transform effects.
Since API version 9, this API is supported in ArkTS widgets.
NOTE The following formulas calculate coordinates of the transformed graph. x and y represent coordinates before transformation, and x’ and y’ represent coordinates after transformation.
x’ = scaleX * x + skewY * y + translateX
y’ = skewX * x + scaleY * y + translateY
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| a | number | Yes | 0 | X-axis scale. |
| b | number | Yes | 0 | X-axis skew. |
| c | number | Yes | 0 | Y-axis skew. |
| d | number | Yes | 0 | Y-axis scale. |
| e | number | Yes | 0 | X-axis translation. |
| f | number | Yes | 0 | Y-axis translation. |
Example
// xxx.ets
@Entry
@Component
struct Transform {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillStyle = 'rgb(0,0,0)'
offContext.fillRect(0, 0, 100, 100)
offContext.transform(1, 0.5, -0.5, 1, 10, 10)
offContext.fillStyle = 'rgb(255,0,0)'
offContext.fillRect(0, 0, 100, 100)
offContext.transform(1, 0.5, -0.5, 1, 10, 10)
offContext.fillStyle = 'rgb(0,0,255)'
offContext.fillRect(0, 0, 100, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
setTransform
setTransform(a: number, b: number, c: number, d: number, e: number, f: number): void
Resets the existing transformation matrix and creates a new transformation matrix by using the same parameters as the transform() API.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| a | number | Yes | 0 | X-axis scale. |
| b | number | Yes | 0 | X-axis skew. |
| c | number | Yes | 0 | Y-axis skew. |
| d | number | Yes | 0 | Y-axis scale. |
| e | number | Yes | 0 | X-axis translation. |
| f | number | Yes | 0 | Y-axis translation. |
Example
// xxx.ets
@Entry
@Component
struct SetTransform {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillStyle = 'rgb(255,0,0)'
offContext.fillRect(0, 0, 100, 100)
offContext.setTransform(1,0.5, -0.5, 1, 10, 10)
offContext.fillStyle = 'rgb(0,0,255)'
offContext.fillRect(0, 0, 100, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
setTransform
setTransform(transform?: Matrix2D): void
Resets the current transformation and creates a new transformation matrix based on the specified Matrix2D object.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| transform | Matrix2D | No | null | Transformation matrix. |
getTransform
getTransform(): Matrix2D
Obtains the current transformation matrix being applied to the context.
Since API version 9, this API is supported in ArkTS widgets.
Return value
| Type | Description |
|---|---|
| Matrix2D | Matrix object. |
Example
// xxx.ets
@Entry
@Component
struct TransFormDemo {
private settings: RenderingContextSettings = new RenderingContextSettings(true);
private context1: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings);
private offcontext1: OffscreenCanvasRenderingContext2D = new OffscreenCanvasRenderingContext2D(600, 100, this.settings);
private context2: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings);
private offcontext2: OffscreenCanvasRenderingContext2D = new OffscreenCanvasRenderingContext2D(600, 100, this.settings);
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Text('context1');
Canvas(this.context1)
.width('230vp')
.height('120vp')
.backgroundColor('#ffff00')
.onReady(() =>{
this.offcontext1.fillRect(50, 50, 50, 50);
this.offcontext1.setTransform(1.2, Math.PI/8, Math.PI/6, 0.5, 30, -25);
this.offcontext1.fillRect(50, 50, 50, 50);
let image = this.offcontext1.transferToImageBitmap();
this.context1.transferFromImageBitmap(image);
})
Text('context2');
Canvas(this.context2)
.width('230vp')
.height('120vp')
.backgroundColor('#0ffff0')
.onReady(() =>{
this.offcontext2.fillRect(50, 50, 50, 50);
let storedTransform = this.offcontext1.getTransform();
console.log("Matrix [scaleX = " + storedTransform.scaleX + ", scaleY = " + storedTransform.scaleY +
", rotateX = " + storedTransform.rotateX + ", rotateY = " + storedTransform.rotateY +
", translateX = " + storedTransform.translateX + ", translateY = " + storedTransform.translateY + "]")
this.offcontext2.setTransform(storedTransform);
this.offcontext2.fillRect(50,50,50,50);
let image = this.offcontext2.transferToImageBitmap();
this.context2.transferFromImageBitmap(image);
})
}
.width('100%')
.height('100%')
}
}
translate
translate(x: number, y: number): void
Moves the origin of the coordinate system.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x | number | Yes | 0 | X-axis translation. |
| y | number | Yes | 0 | Y-axis translation. |
Example
// xxx.ets
@Entry
@Component
struct Translate {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.fillRect(10, 10, 50, 50)
offContext.translate(70, 70)
offContext.fillRect(10, 10, 50, 50)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
drawImage
drawImage(image: ImageBitmap|PixelMap, dx: number, dy: number): void
drawImage(image: ImageBitmap|PixelMap, dx: number, dy: number, dw: number, dh: number): void
drawImage(image: ImageBitmap|PixelMap, sx: number, sy: number, sw: number, sh: number, dx: number, dy: number, dw: number, dh: number):void
Draws an image on the canvas.
Since API version 9, this API is supported in ArkTS widgets, except that PixelMap objects are not supported.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| image | ImageBitmap or PixelMap | Yes | null | Image resource. For details, see ImageBitmap or PixelMap. |
| sx | number | No | 0 | X-coordinate of the upper left corner of the rectangle used to crop the source image. |
| sy | number | No | 0 | Y-coordinate of the upper left corner of the rectangle used to crop the source image. |
| sw | number | No | 0 | Target width to crop the source image. |
| sh | number | No | 0 | Target height to crop the source image. |
| dx | number | Yes | 0 | X-coordinate of the upper left corner of the drawing area on the canvas. |
| dy | number | Yes | 0 | Y-coordinate of the upper left corner of the drawing area on the canvas. |
| dw | number | No | 0 | Width of the drawing area. |
| dh | number | No | 0 | Height of the drawing area. |
Example
// xxx.ets
@Entry
@Component
struct DrawImage {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private img:ImageBitmap = new ImageBitmap("common/images/icon.jpg")
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() => {
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.drawImage( this.img,0,0,400,200)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
createImageData
createImageData(sw: number, sh: number): ImageData
Creates an ImageData object with the specified dimensions.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| sw | number | Yes | 0 | Width of the ImageData object. |
| sh | number | Yes | 0 | Height of the ImageData object. |
createImageData(imageData: ImageData): ImageData
Creates an ImageData object by copying an existing ImageData object.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| imagedata | ImageData | Yes | null | ImageData object to copy. |
Return value
| Type | Description |
|---|---|
| ImageData | New ImageData object. |
getPixelMap
getPixelMap(sx: number, sy: number, sw: number, sh: number): PixelMap
Obtains the PixelMap object created with the pixels within the specified area on the canvas.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| sx | number | Yes | 0 | X-coordinate of the upper left corner of the output area. |
| sy | number | Yes | 0 | Y-coordinate of the upper left corner of the output area. |
| sw | number | Yes | 0 | Width of the output area. |
| sh | number | Yes | 0 | Height of the output area. |
Return value
| Type | Description |
|---|---|
| PixelMap | PixelMap object. |
setPixelMap
setPixelMap(value?: PixelMap): void
Draws the input PixelMap object on the canvas.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| sx | number | Yes | 0 | X-coordinate of the upper left corner of the output area. |
| sy | number | Yes | 0 | Y-coordinate of the upper left corner of the output area. |
| sw | number | Yes | 0 | Width of the output area. |
| sh | number | Yes | 0 | Height of the output area. |
Return value
| Type | Description |
|---|---|
| PixelMap | PixelMap object. |
getImageData
getImageData(sx: number, sy: number, sw: number, sh: number): ImageData
Obtains the ImageData object created with the pixels within the specified area on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| sx | number | Yes | 0 | X-coordinate of the upper left corner of the output area. |
| sy | number | Yes | 0 | Y-coordinate of the upper left corner of the output area. |
| sw | number | Yes | 0 | Width of the output area. |
| sh | number | Yes | 0 | Height of the output area. |
Return value
| Type | Description |
|---|---|
| ImageData | New ImageData object. |
Example
// xxx.ets
@Entry
@Component
struct GetImageData {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
private img:ImageBitmap = new ImageBitmap("/common/images/1234.png")
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.drawImage(this.img,0,0,130,130)
let imagedata = offContext.getImageData(50,50,130,130)
offContext.putImageData(imagedata,150,150)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
putImageData
putImageData(imageData: Object, dx: number|string, dy: number|string): void
putImageData(imageData: Object, dx: number|string, dy: number|string, dirtyX: number|string, dirtyY: number|string, dirtyWidth?: number|string, dirtyHeight: number|string): void
Puts an ImageData object onto a rectangular area on the canvas.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| imagedata | Object | Yes | null | ImageData object with pixels to put onto the canvas. |
| dx | number |string10+ | Yes | 0 | X-axis offset of the rectangular area on the canvas. |
| dy | number |string10+ | Yes | 0 | Y-axis offset of the rectangular area on the canvas. |
| dirtyX | number |string10+ | No | 0 | X-axis offset of the upper left corner of the rectangular area relative to that of the source image. |
| dirtyY | number |string10+ | No | 0 | Y-axis offset of the upper left corner of the rectangular area relative to that of the source image. |
| dirtyWidth | number |string10+ | No | Width of the ImageData object | Width of the rectangular area to crop the source image. |
| dirtyHeight | number |string10+ | No | Height of the ImageData object | Height of the rectangular area to crop the source image. |
Example
// xxx.ets
@Entry
@Component
struct PutImageData {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let imageData = offContext.createImageData(100, 100)
for (let i = 0; i < imageData.data.length; i += 4) {
imageData.data[i + 0] = 255
imageData.data[i + 1] = 0
imageData.data[i + 2] = 255
imageData.data[i + 3] = 255
}
offContext.putImageData(imageData, 10, 10)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
setLineDash
setLineDash(segments: number[]): void
Sets the dash line style.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Description |
|---|---|---|
| segments | number[] | An array of numbers that specify distances to alternately draw a line and a gap. |
Example
@Entry
@Component
struct SetLineDash {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.arc(100, 75, 50, 0, 6.28)
offContext.setLineDash([10,20])
offContext.stroke()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
getLineDash
getLineDash(): number[]
Obtains the dash line style.
Since API version 9, this API is supported in ArkTS widgets.
Return value
| Type | Description |
|---|---|
| number[] | An array describing the interval of alternate line segments and length of spacing. |
Example
// xxx.ets
@Entry
@Component
struct OffscreenCanvasGetLineDash {
@State message: string = 'Hello World'
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Row() {
Column() {
Text(this.message)
.fontSize(50)
.fontWeight(FontWeight.Bold)
.onClick(()=>{
console.error('before getlinedash clicked')
let offContext = this.offCanvas.getContext("2d", this.settings)
let res = offContext.getLineDash()
console.error(JSON.stringify(res))
})
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() => {
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.arc(100, 75, 50, 0, 6.28)
offContext.setLineDash([10,20])
offContext.stroke()
let res = offContext.getLineDash()
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
}
.height('100%')
}
}
toDataURL
toDataURL(type?: string, quality?: number): string
Generates a URL containing image display information.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Description |
|---|---|---|---|
| type | string | No | Image format. The default value is image/png. |
| quality | number | No | Image quality, which ranges from 0 to 1, when the image format is image/jpeg or image/webp. If the set value is beyond the value range, the default value 0.92 is used. |
Return value
| Type | Description |
|---|---|
| string | Image URL. |
Example
// xxx.ets
@Entry
@Component
struct ToDataURL {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let dataURL = offContext.toDataURL()
})
}
.width('100%')
.height('100%')
}
}
imageSmoothingQuality
imageSmoothingQuality(quality: imageSmoothingQuality)
Sets the quality of image smoothing.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Description |
|---|---|---|
| quality | imageSmoothingQuality | Quality of image smoothing. - ‘low’: low quality. - ‘medium’: medium quality. - ‘high’: high quality. |
Example
// xxx.ets
@Entry
@Component
struct ImageSmoothingQualityDemoOff {
private settings: RenderingContextSettings = new RenderingContextSettings(true);
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings);
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
private img:ImageBitmap = new ImageBitmap("common/images/example.jpg");
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let offctx = offContext
offctx.imageSmoothingEnabled = true
offctx.imageSmoothingQuality = 'high'
offctx.drawImage(this.img, 0, 0, 400, 200)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
transferToImageBitmap
transferToImageBitmap(): ImageBitmap
Creates an ImageBitmap object on the most recently rendered image of the OffscreenCanvas.
Return value
| Type | Description |
|---|---|
| ImageBitmap | Pixel data rendered on the OffscreenCanvas. |
Example
// xxx.ets
@Entry
@Component
struct PutImageData {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let imageData = offContext.createImageData(100, 100)
for (let i = 0; i < imageData.data.length; i += 4) {
imageData.data[i + 0] = 255
imageData.data[i + 1] = 0
imageData.data[i + 2] = 255
imageData.data[i + 3] = 255
}
offContext.putImageData(imageData, 10, 10)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
restore
restore(): void
Restores the saved drawing context.
Since API version 9, this API is supported in ArkTS widgets.
Example
// xxx.ets
@Entry
@Component
struct CanvasExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.save() // save the default state
offContext.fillStyle = "#00ff00"
offContext.fillRect(20, 20, 100, 100)
offContext.restore() // restore to the default state
offContext.fillRect(150, 75, 100, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
save
save(): void
Saves the current drawing context.
Since API version 9, this API is supported in ArkTS widgets.
Example
// xxx.ets
@Entry
@Component
struct CanvasExample {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
offContext.save() // save the default state
offContext.fillStyle = "#00ff00"
offContext.fillRect(20, 20, 100, 100)
offContext.restore() // restore to the default state
offContext.fillRect(150, 75, 100, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
createLinearGradient
createLinearGradient(x0: number, y0: number, x1: number, y1: number): void
Creates a linear gradient.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x0 | number | Yes | 0 | X-coordinate of the start point. |
| y0 | number | Yes | 0 | Y-coordinate of the start point. |
| x1 | number | Yes | 0 | X-coordinate of the end point. |
| y1 | number | Yes | 0 | Y-coordinate of the end point. |
Example
// xxx.ets
@Entry
@Component
struct CreateLinearGradient {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let grad = offContext.createLinearGradient(50,0, 300,100)
grad.addColorStop(0.0, '#ff0000')
grad.addColorStop(0.5, '#ffffff')
grad.addColorStop(1.0, '#00ff00')
offContext.fillStyle = grad
offContext.fillRect(0, 0, 400, 400)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
createRadialGradient
createRadialGradient(x0: number, y0: number, r0: number, x1: number, y1: number, r1: number): void
Creates a linear gradient.
Since API version 9, this API is supported in ArkTS widgets.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| x0 | number | Yes | 0 | X-coordinate of the center of the start circle. |
| y0 | number | Yes | 0 | Y-coordinate of the center of the start circle. |
| r0 | number | Yes | 0 | Radius of the start circle, which must be a non-negative finite number. |
| x1 | number | Yes | 0 | X-coordinate of the center of the end circle. |
| y1 | number | Yes | 0 | Y-coordinate of the center of the end circle. |
| r1 | number | Yes | 0 | Radius of the end circle, which must be a non-negative finite number. |
Example
// xxx.ets
@Entry
@Component
struct CreateRadialGradient {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffff00')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let grad = offContext.createRadialGradient(200,200,50, 200,200,200)
grad.addColorStop(0.0, '#ff0000')
grad.addColorStop(0.5, '#ffffff')
grad.addColorStop(1.0, '#00ff00')
offContext.fillStyle = grad
offContext.fillRect(0, 0, 440, 440)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
createConicGradient10+
createConicGradient(startAngle: number, x: number, y: number): CanvasGradient
Creates a conic gradient.
Parameters
| Name | Type | Mandatory | Default Value | Description |
|---|---|---|---|---|
| startAngle | number | Yes | 0 | Angle at which the gradient starts, in radians. The angle measurement starts horizontally from the right side of the center and moves clockwise. |
| x | number | Yes | 0 | X-coordinate of the center of the conic gradient, in vp. |
| y | number | Yes | 0 | Y-coordinate of the center of the conic gradient, in vp. |
Example
// xxx.ets
@Entry
@Component
struct OffscreenCanvasConicGradientPage {
private settings: RenderingContextSettings = new RenderingContextSettings(true)
private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
build() {
Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
Canvas(this.context)
.width('100%')
.height('100%')
.backgroundColor('#ffffff')
.onReady(() =>{
let offContext = this.offCanvas.getContext("2d", this.settings)
let grad = offContext.createConicGradient(0, 50, 80)
grad.addColorStop(0.0, '#ff0000')
grad.addColorStop(0.5, '#ffffff')
grad.addColorStop(1.0, '#00ff00')
offContext.fillStyle = grad
offContext.fillRect(0, 30, 100, 100)
let image = this.offCanvas.transferToImageBitmap()
this.context.transferFromImageBitmap(image)
})
}
.width('100%')
.height('100%')
}
}
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