Image Transformation (C/C++)

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:

Open src/main/cpp/hello.cpp, and add the reference file.

#include<multimedia/image_framework/image_pixel_map_napi.h>

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

   import image from '@ohos.multimedia.image'
   export const add:(a: number, b: number) => image.PixelMap;
   export const transform: (a: image.PixelMap) => image.PixelMap;
   export const testGetImageInfo: (a: image.PixelMap) => image.PixelMap;
   export const testAccessPixels: (a: image.PixelMap) => image.PixelMap;
   export const testUnAccessPixels: (a: image.PixelMap) => image.PixelMap;
   

2. 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 '@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%')
   }
   }