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:

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;
}

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;
}

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

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

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%')
}
}