harmony 鸿蒙Image Transformation (Native)

  • 2023-06-24
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Image Transformation (Native)

You will learn how to use native image APIs to process images.

How to Develop

Adding Dependencies

Open the src/main/cpp/CMakeLists.txt file of the native project, add libpixelmap_ndk.z.so of the image and libhilog_ndk.z.so of the log 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[] = {
        { "testGetImageInfo", nullptr, TestGetImageInfo, nullptr, nullptr, nullptr, napi_default, nullptr },
        { "testAccessPixels", nullptr, TestAccessPixels, nullptr, nullptr, nullptr, napi_default, nullptr },
        { "testUnAccessPixels", nullptr, TestUnAccessPixels, 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 API Reference.

Obtain the JS resource object from the hello.cpp file and convert it to a native resource object. Then you can call native APIs. The sample code is as follows:

  1. Obtain the PixelMap information and store the information to the OhosPixelMapInfo struct.

    static napi_value TestGetImageInfo(napi_env env, napi_callback_info info)
    {
        napi_value result = nullptr;
        napi_get_undefined(env, &result);
    
    
        napi_value thisVar = nullptr;
        napi_value argValue[1] = {0};
        size_t argCount = 1;
    
    
        napi_get_cb_info(env, info, &argCount, argValue, &thisVar, nullptr);
    
    
        OHOS::Media::OhosPixelMapInfo pixelMapInfo;
        OHOS::Media::OH_GetImageInfo(env, argValue[0], &pixelMapInfo);
        return result;
    }
    
  2. Obtain the memory address of a PixelMap object and lock the memory.

    static napi_value TestAccessPixels(napi_env env, napi_callback_info info)
    {
        napi_value result = nullptr;
        napi_get_undefined(env, &result);
    
    
        napi_value thisVar = nullptr;
        napi_value argValue[1] = {0};
        size_t argCount = 1;
    
    
        napi_get_cb_info(env, info, &argCount, argValue, &thisVar, nullptr);
    
    
        void* addrPtr = nullptr;
        OHOS::Media::OH_AccessPixels(env, argValue[0], &addrPtr);
        return result;
    }
    
  3. Unlock the memory of the PixelMap object.

    static napi_value TestUnAccessPixels(napi_env env, napi_callback_info info)
    {
        napi_value result = nullptr;
        napi_get_undefined(env, &result);
    
    
        napi_value thisVar = nullptr;
        napi_value argValue[1] = {0};
        size_t argCount = 1;
    
    
        napi_get_cb_info(env, info, &argCount, argValue, &thisVar, nullptr);
    
    
        OHOS::Media::OH_UnAccessPixels(env, argValue[0]);
        return result;
    }
    

Calling APIs on the JS Side

  1. Open src\main\ets\pages\index.ets, and import libentry.so.

  2. 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 '@ohos.multimedia.image';
    
    
    @Entry
    @Component
    struct Index {
    @State message: string = 'IMAGE'
    @State _PixelMap : image.PixelMap|undefined = undefined;
    
    
    build() {
        Row() {
        Column() {
            Button(this.message)
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
            .onClick(() => {
                const color : ArrayBuffer = new ArrayBuffer(96);
                let opts: image.InitializationOptions = { alphaType: 0, editable: true, pixelFormat: 4, scaleMode: 1, size: { height: 4, width: 6 } }
                image.createPixelMap(color, opts)
                .then( (pixelmap : image.PixelMap) => {
                    this._PixelMap = pixelmap;
                })
    
    
                testNapi.testGetImageInfo(this._PixelMap);
                console.info("Test GetImageInfo success");
    
    
                testNapi.testAccessPixels(this._PixelMap);
                console.info("Test AccessPixels success");
    
    
                testNapi.testUnAccessPixels(this._PixelMap);
                console.info("Test UnAccessPixels success");
            })
        }
        .width('100%')
        }
        .height('100%')
    }
    }
    

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