harmony 鸿蒙PixelMap Operation

2025-06-12
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PixelMap Operation

This topic describes how to use native image APIs to perform PixelMap operations.

How to Develop

Adding Dependencies

Open the src/main/cpp/CMakeLists.txt file of the native project, add libace_napi.z.so and libpixelmap_ndk.z.so (on both of which the image APIs depend) and libhilog_ndk.z.so (on which the log APIs depend) to the target_link_libraries dependency.

target_link_libraries(entry PUBLIC libace_napi.z.so libhilog_ndk.z.so libpixelmap_ndk.z.so)

Adding API Mappings

Open the src/main/cpp/hello.cpp file and add the following API mappings to the Init function:

EXTERN_C_START
static napi_value Init(napi_env env, napi_value exports)
{
    napi_property_descriptor desc[] = {
        { "createPixelMapTest", nullptr, CreatePixelMapTest, nullptr, nullptr, nullptr, napi_default, nullptr },
        { "createAlphaPixelMap", nullptr, CreateAlphaPixelMap, nullptr, nullptr, nullptr, napi_default, nullptr },
        { "transform", nullptr, Transform, nullptr, nullptr, nullptr, napi_default, nullptr },
    };

    napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc);
    return exports;
}
EXTERN_C_END

Calling the Native APIs

For details about the APIs, see Image.

Obtain the JS resource object from the hello.cpp file and convert it to a native resource object. Then you can call native APIs.

Adding Reference Files

#include <multimedia/image_framework/image_mdk_common.h>
#include <multimedia/image_framework/image_pixel_map_mdk.h>
#include <stdlib.h>

Create a PixelMap object.

napi_value CreatePixelMapTest(napi_env env, napi_callback_info info) {
    napi_value udfVar = nullptr;
    napi_value pixelMap = nullptr;


    struct OhosPixelMapCreateOps createOps;
    createOps.width = 4;
    createOps.height = 6;
    createOps.pixelFormat = 4;
    createOps.alphaType = 0;
    size_t bufferSize = createOps.width * createOps.height * 4;
    void *buff = malloc(bufferSize);
    if (buff == nullptr) {
        return udfVar;
    }


    char *cc = (char *)buff;
    for (int i = 0; i < 96; i++) {
        *(cc++) = (char)i;
    }
    int32_t res = OH_PixelMap_CreatePixelMap(env, createOps, (uint8_t *)buff, bufferSize, &pixelMap);
    free(buff);
    if (res != IMAGE_RESULT_SUCCESS||pixelMap == nullptr) {
        return udfVar;
    }
    return pixelMap;
}

Create a PixelMap object that contains only alpha channel information.

napi_value CreateAlphaPixelMap(napi_env env, napi_callback_info info) {
    napi_value udfVar = nullptr;
    napi_value thisVar = nullptr;
    napi_value argValue[1] = {0};
    size_t argCount = 1;


    napi_value alphaPixelMap = nullptr;


    napi_get_undefined(env, &udfVar);


    if (napi_get_cb_info(env, info, &argCount, argValue, &thisVar, nullptr) != napi_ok||argCount < 1||
        argValue[0] == nullptr) {
        return udfVar;
    }
    int32_t res = OH_PixelMap_CreateAlphaPixelMap(env, argValue[0], &alphaPixelMap);
    if (res != IMAGE_RESULT_SUCCESS||alphaPixelMap == nullptr) {
        return udfVar;
    }
    return alphaPixelMap;
}

Process the PixelMap object.

napi_value Transform(napi_env env, napi_callback_info info) {
    napi_value thisVar = nullptr;
    napi_value argValue[1] = {0};
    size_t argCount = 1;


    if (napi_get_cb_info(env, info, &argCount, argValue, &thisVar, nullptr) != napi_ok||argCount < 1||
        argValue[0] == nullptr) {
        return nullptr;
    }
    napi_value result = nullptr;
    napi_get_undefined(env, &result);


    // Initialize a NativePixelMap object.
    NativePixelMap *native = OH_PixelMap_InitNativePixelMap(env, argValue[0]);
    if (native == nullptr) {
        return result;
    }


    // Obtain image information.
    struct OhosPixelMapInfos pixelMapInfo;
    OH_PixelMap_GetImageInfo(native, &pixelMapInfo);


    // Obtain the number of bytes per row of the PixelMap object.
    int32_t rowBytes;
    OH_PixelMap_GetBytesNumberPerRow(native, &rowBytes);


    // Check whether the PixelMap object is editable.
    int32_t editable = 0;
    OH_PixelMap_GetIsEditable(native, &editable);


    // Check whether the PixelMap object supports alpha channels.
    int32_t supportAlpha = 0;
    OH_PixelMap_IsSupportAlpha(native, &supportAlpha);


    // Set an alpha channel for the PixelMap object.
    int32_t alphaAble = 0;
    OH_PixelMap_SetAlphaAble(native, alphaAble);


    // Obtain the pixel density of the PixelMap object.
    int32_t densityG;
    OH_PixelMap_GetDensity(native, &densityG);


    // Set the pixel density for the PixelMap object.
    int32_t densityS = 100;
    OH_PixelMap_SetDensity(native, densityS);


    // Set the opacity for the PixelMap object.
    float opacity = 0.5;
    OH_PixelMap_SetOpacity(native, opacity);


    // Scale the image.
    // scaleX: The width of the image after scaling is 0.5 of the original width.
    // scaleY: The height of the image after scaling is 0.5 of the original height.
    float scaleX = 0.5;
    float scaleY = 0.5;
    OH_PixelMap_Scale(native, scaleX, scaleY);


    // Translate the image.
    // translateX: Translate the image by 50 units downwards.
    // translateY: Translate the image by 50 units rightwards.
    float translateX = 50;
    float translateY = 50;
    OH_PixelMap_Translate(native, translateX, translateY);


    // Rate the image clockwise by 90°.
    float angle = 90;
    OH_PixelMap_Rotate(native, angle);


    // Flip the image.
    // flipX: whether to flip the image horizontally. The value 1 means to flip the image and 0 means the opposite.
    // flipY: whether to flip the image vertically. The value 1 means to flip the image and 0 means the opposite.
    int32_t flipX = 0;
    int32_t flipY = 1;
    OH_PixelMap_Flip(native, flipX, flipY);


    // Crop the image.
    // cropX: x-axis coordinate of the start point for cropping.
    // cropY: y-axis coordinate of the start point for cropping.
    // cropH: height after cropping (10), cropping from top to bottom.
    // cropW: width after cropping (10), cropping from left to right.
    int32_t cropX = 1;
    int32_t cropY = 1;
    int32_t cropW = 10;
    int32_t cropH = 10;
    OH_PixelMap_Crop(native, cropX, cropY, cropW, cropH);


    // Obtain the memory address of the PixelMap object and lock the memory.
    void *pixelAddr = nullptr;
    OH_PixelMap_AccessPixels(native, &pixelAddr);


    // Unlock the memory of the PixelMap object.
    OH_PixelMap_UnAccessPixels(native);


    return result;
}

Calling APIs on the JS Side

Open src\main\cpp\types*libentry*\index.d.ts (where libentry varies according to the project name), and import the following files:

import { image } from '@kit.ImageKit';


export const createPixelMapTest: () => image.PixelMap;
export const transform: (a: image.PixelMap) => void;

Open src\main\ets\pages\index.ets, import *libentry*.so (where libentry varies according to the project name), call the native APIs, and pass in the JS resource object. The sample code is as follows:

import testNapi from 'libentry.so';
import { image } from '@kit.ImageKit';


@Entry
@Component
struct Index {
@State _pixelMap : image.PixelMap|undefined = undefined;


build() {
    Row() {
        Column() {
            Button("PixelMap")
            .width(100)
            .height(100)
            .onClick(() => {
                console.log("com.example.native_ndk_api10 button click in");
                this._pixelMap = testNapi.createPixelMapTest();
                testNapi.transform(this._pixelMap);
            })
            Image(this._pixelMap)
            .width(500)
            .height(500)
            .objectFit(ImageFit.Cover)
            .border({width: 1, color: Color.Blue})
            }
            .width('100%')
        }
        .height('100%')
    }
}