harmony 鸿蒙XComponent

2023-06-24
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XComponent

As a drawing component, the <XComponent> is usually used to meet relatively complex drawing customization requirements, for example, display of a camera preview stream and drawing of a game image.

You can specify the type parameter to implement different features. Two options are mainly available for this parameter: surface and component.

With the <XComponent> of the surface type, you can pass data to the surface independently owned by it to render the image.

With the <XComponent> of the component type, you can dynamically load the displayed content.

surface Type

When the <XComponent> is set to the surface type, you can write EGL/OpenGL ES and media data and display it on the <XComponent>.

You can also have the <XComponent> laid out and rendered together with other components.

The <XComponent> has an independent surface, which provides a native window for you to create the EGL/OpenGL ES environment on the native (C/C++) side and use the standard OpenGL ES for development.

In addition, media-related applications (such as videos and cameras) can write data to the surface provided by the <XComponent> to present the corresponding image.

Using EGL/OpenGL ES for Rendering

Key Points of Native Code Development

OpenHarmony applications use native APIs to implement interactions between JS and C/C++ code. This is also the case with the <XComponent>. For details, see Using N-APIs in Application Projects.

The type of the file for processing the JS logic on the native side is .so.

Each module has a .so file.
The .so file is named in the format of lib{moduleName}.so.

In the scenario where the <XComponent> is used for standard OpenGL ES development, the content of the CMAKELists.txt file is as follows:

cmake_minimum_required(VERSION 3.4.1)
project(XComponent) # Project name

set(NATIVERENDER_ROOT_PATH ${CMAKE_CURRENT_SOURCE_DIR})
# Path for searching for header files
include_directories(${NATIVERENDER_ROOT_PATH}
                    ${NATIVERENDER_ROOT_PATH}/include
                    )

# Compile the target .so file. SHARED indicates the dynamic library.
add_library(nativerender SHARED
            xxx.cpp
            )

# Search for related libraries (including OpenGL ES libraries and NDK APIs provided by the <XComponent>).
find_library( EGL-lib
              EGL )

find_library( GLES-lib
              GLESv3 )

find_library( libace-lib
              ace_ndk.z )

# Dependencies required for compiling .so files
target_link_libraries(nativerender PUBLIC ${EGL-lib} ${GLES-lib} ${libace-lib} libace_napi.z.so libc++.a)

Registering the N-API Module

static napi_value Init(napi_env env, napi_value exports)
{
	// Define the API exposed on the module.
    napi_property_descriptor desc[] ={
        DECLARE_NAPI_FUNCTION("changeColor", PluginRender::NapiChangeColor),
    };
    // You can mount the native method (PluginRender::NapiChangeColor) to exports through this API. exports is bound to a JS object at the JS layer through the JS engine.
    NAPI_CALL(env, napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc));
    return exports;
}

static napi_module nativerenderModule = {
    .nm_version = 1,
    .nm_flags = 0,
    .nm_filename = nullptr,
    .nm_register_func = Init, // Specify the callback for when the corresponding module is loaded.
    .nm_modname = "nativerender", // Specify the module name. For <XComponent>-related development, the name must be the same as the value of libraryname in the <XComponent> on ArkTS.
    .nm_priv = ((void*)0),
    .reserved = { 0 },
};

extern "C" __attribute__((constructor)) void RegisterModule(void)
{
    // Register the SO module.
    napi_module_register(&nativerenderModule);c
}

Parsing the NativeXComponent Instance

NativeXComponent provides an instance at the native layer for the <XComponent>, which can be used as a bridge for binding with the <XComponent> at the JS layer. The NDK APIs provided by the <XComponent> depend on this instance. For details about the NDK APIs, see Native XComponent.

The NativeXComponent instance can be obtained by parsing the callback (that is, the Init function in NAPI module registration) when the module is loaded.

{
    // ...
    napi_status status;
    napi_value exportInstance = nullptr;
    OH_NativeXComponent *nativeXComponent = nullptr;
    // Parse the attribute of the wrapped NativeXComponent pointer.
    status = napi_get_named_property(env, exports, OH_NATIVE_XCOMPONENT_OBJ, &exportInstance);
    if (status != napi_ok) {
        return false;
    }
    // Use the napi_unwrap API to parse the NativeXComponent instance pointer.
    status = napi_unwrap(env, exportInstance, reinterpret_cast<void**>(&nativeXComponent));
    // ...
}

Registering XComponent Callback

Based on the NativeXComponent pointer obtained by parsing the NativeXComponent instance, perform callback registration through the OH_NativeXComponent_RegisterCallback API.

{
    ...
    OH_NativeXComponent *nativeXComponent = nullptr;
    // Parse the NativeXComponent instance.

    OH_NativeXComponent_Callback callback;
    callback->OnSurfaceCreated = OnSurfaceCreatedCB; // Invoked when a surface is successfully created. You can obtain the handle to the native window from this event.
    callback->OnSurfaceChanged = OnSurfaceChangedCB; // Invoked when the surface changes. You can obtain the native window handle and XComponent change information from this event.
    callback->OnSurfaceDestroyed = OnSurfaceDestroyedCB; // Invoked when the surface is destroyed. You can release resources in this event.
    callback->DispatchTouchEvent = DispatchTouchEventCB; // Invoked when a touch event occurs. You can obtain the touch event information from this event.

    OH_NativeXComponent_RegisterCallback(nativeXComponent, callback);
    ...
}

Creating the EGL/OpenGL ES Environment

In the registered OnSurfaceCreated callback, you can obtain the handle to the native window (which is essentially the surface independently owned by the <XComponent>). Therefore, you can create the EGL/OpenGL ES environment for your application to start the development of the rendering logic.

EGLCore* eglCore_; // EGLCore is a class that encapsulates OpenGL-related APIs.
uint64_t width_;
uint64_t height_;
void OnSurfaceCreatedCB(OH_NativeXComponent* component, void* window)
{
    int32_t ret = OH_NativeXComponent_GetXComponentSize(component, window, &width_, &height_);
    if (ret === OH_NATIVEXCOMPONENT_RESULT_SUCCESS) {
        eglCore_->GLContextInit(window, width_, height_); // Initialize the OpenGL environment.
    }
}

ArkTS Syntax

You can use the <XComponent> to develop EGL/OpenGL ES rendering by using the following code on the ArkTS side:

XComponent({ id: 'xcomponentId1', type: 'surface', libraryname: 'nativerender' })
  .onLoad((context) => {})
  .onDestroy(() => {})

id: corresponds to an <XComponent> and must be unique. Generally, you can use the OH_NativeXComponent_GetXComponentId API on the native side to obtain the corresponding ID and bind the corresponding <XComponent>.
libraryname: name of the loaded module, which must be the same as the value of nm_modname used when the Napi module is registered on the native side.

NOTE

An application loads modules to implement cross-language invoking in either of the following modes:

Use the import mode of the NAPI.

  > import nativerender from "libnativerender.so"
  > ```
  >
  > 2. Use the **\<XComponent>**.
  >
  >    While this mode also uses the NAPI mechanism as the **import** mode, it enables you to use the NDK APIs of the **\<XComponent>**, by having the **NativeXComponent** instance of the **\<XComponent>** exposed to the native layer of the application when the dynamic library is loaded.

- **onLoad** event
  - Trigger time: when the surface of the **\<XComponent>** is ready.
  - **context** parameter: where the native API exposed on the module is mounted. Its usage is similar to the usage of the **context2** instance obtained after the module is directly loaded using **import context2 from "libnativerender.so"**.
  - Time sequence: subject to the surface. The figure below shows the time sequence of the **onLoad** event and the **OnSurfaceCreated** event at the native layer.

     ![onLoad](figures/onLoad.png)

- **onDestroy** event

  Trigger time: when the **\<XComponent>** is destroyed, in the same manner as that when an ArkUI component is destroyed. The figure below shows the time sequence of the **onDestroy** event and the **OnSurfaceDestroyed** event at the native layer.

  ![onDestroy](figures/onDestroy.png)


### Writing Media Data

The surface held by the **\<XComponent>** complies with the producer-consumer model.

In OpenHarmony, components that comply with the producer design, such as the Camera and AVPlayer components, can write data to the surface held by the **\<XComponent>** and display the data through the **\<XComponent>**.

![picture-1](figures/picture-1.png)

You can bind the **\<XComponent>** to the **XComponentController** to obtain the surface ID (**surfaceId**, which uniquely identifies a surface) and send it to the corresponding component API.


```ts
class suf{
  surfaceId:string = "";
  mXComponentController: XComponentController = new XComponentController();
  set(){
    this.surfaceId = this.mXComponentController.getXComponentSurfaceId()
  }
}
@State surfaceId:string = "";
mXComponentController: object = new XComponentController();
XComponent({ id: '', type: 'surface', controller: this.mXComponentController })
  .onLoad(() => {
    let sufset = new suf()
    sufset.set()
  })

For details about component APIs, see AVPlayer and Camera.

component Type

When the <XComponent> is set to the component type, you can execute non-UI logic to dynamically load the displayed content.

NOTE

When type is set to component, the <XComponent> functions as a container, where child components are laid out vertically.

Vertical alignment: FlexAlign.Start

Horizontal alignment: FlexAlign.Center

The component does not respond to any events.

Layout changes and event responses can be set by mounting child components.

The non-UI logic written internally needs to be encapsulated in one or more functions.

Example Scenario

@Builder
function addText(label: string): void {
  Text(label)
    .fontSize(40)
}

@Entry
@Component
struct Index {
  @State message: string = 'Hello XComponent'
  @State messageCommon: string = 'Hello World'
  build() {
    Row() {
      Column() {
        XComponent({ id: 'xcomponentId-container', type: 'component' }) {
          addText(this.message)
          Divider()
            .margin(4)
            .strokeWidth(2)
            .color('#F1F3F5')
            .width("80%")
          Column() {
            Text(this.messageCommon)
              .fontSize(30)
          }
        }
      }
      .width('100%')
    }
    .height('100%')
  }
}

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