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1# Image Transformation (C/C++)
2
3You will learn how to use native image APIs to process images.
4
5## How to Develop
6
7**Adding Dependencies**
8
9Open 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.
10
11```txt
12target_link_libraries(entry PUBLIC libace_napi.z.so libhilog_ndk.z.so libpixelmap_ndk.z.so)
13```
14
15**Adding API Mappings**
16
17Open the **src/main/cpp/hello.cpp** file and add the following API mappings to the **Init** function:
18
19```c++
20EXTERN_C_START
21static napi_value Init(napi_env env, napi_value exports)
22{
23    napi_property_descriptor desc[] = {
24        { "testGetImageInfo", nullptr, TestGetImageInfo, nullptr, nullptr, nullptr, napi_default, nullptr },
25        { "testAccessPixels", nullptr, TestAccessPixels, nullptr, nullptr, nullptr, napi_default, nullptr },
26        { "testUnAccessPixels", nullptr, TestUnAccessPixels, nullptr, nullptr, nullptr, napi_default, nullptr },
27    };
28
29    napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc);
30    return exports;
31}
32EXTERN_C_END
33```
34
35
36**Calling the Native APIs**
37
38For details about the APIs, see [Image API Reference](../reference/apis-image-kit/image.md).
39
40Obtain 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:
41
42Open **src/main/cpp/hello.cpp**, and add the reference file.
43```c++
44#include<multimedia/image_framework/image_pixel_map_napi.h>
45```
46
471. Obtain the **PixelMap** information and store the information to the **OhosPixelMapInfo** struct.
48   ```c++
49   static napi_value TestGetImageInfo(napi_env env, napi_callback_info info)
50    {
51        napi_value result = nullptr;
52        napi_get_undefined(env, &result);
53
54        napi_value thisVar = nullptr;
55        napi_value argValue[1] = {0};
56        size_t argCount = 1;
57
58        napi_get_cb_info(env, info, &argCount, argValue, &thisVar, nullptr);
59
60        OHOS::Media::OhosPixelMapInfo pixelMapInfo;
61        OHOS::Media::OH_GetImageInfo(env, argValue[0], &pixelMapInfo);
62        return result;
63    }
64    ```
652. Obtain the memory address of a **PixelMap** object and lock the memory.
66    ```c++
67    static napi_value TestAccessPixels(napi_env env, napi_callback_info info)
68    {
69        napi_value result = nullptr;
70        napi_get_undefined(env, &result);
71
72        napi_value thisVar = nullptr;
73        napi_value argValue[1] = {0};
74        size_t argCount = 1;
75
76        napi_get_cb_info(env, info, &argCount, argValue, &thisVar, nullptr);
77
78        void* addrPtr = nullptr;
79        OHOS::Media::OH_AccessPixels(env, argValue[0], &addrPtr);
80        return result;
81    }
82    ```
833. Unlock the memory of the **PixelMap** object.
84    ```c++
85    static napi_value TestUnAccessPixels(napi_env env, napi_callback_info info)
86    {
87        napi_value result = nullptr;
88        napi_get_undefined(env, &result);
89
90        napi_value thisVar = nullptr;
91        napi_value argValue[1] = {0};
92        size_t argCount = 1;
93
94        napi_get_cb_info(env, info, &argCount, argValue, &thisVar, nullptr);
95
96        OHOS::Media::OH_UnAccessPixels(env, argValue[0]);
97        return result;
98    }
99    ```
100
101**Calling APIs on the JS Side**
102
1031. Open **src\main\cpp\types\*libentry*\index.d.ts** (where **libentry** varies according to the project name), and import the following files:
104    ```js
105    import image from '@ohos.multimedia.image'
106    export const add:(a: number, b: number) => image.PixelMap;
107    export const transform: (a: image.PixelMap) => image.PixelMap;
108    export const testGetImageInfo: (a: image.PixelMap) => image.PixelMap;
109    export const testAccessPixels: (a: image.PixelMap) => image.PixelMap;
110    export const testUnAccessPixels: (a: image.PixelMap) => image.PixelMap;
111    ```
112
1132. 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:
114
115    ```js
116    import testNapi from 'libentry.so'
117    import image from '@ohos.multimedia.image';
118
119    @Entry
120    @Component
121    struct Index {
122    @State message: string = 'IMAGE'
123    @State _PixelMap : image.PixelMap | undefined = undefined;
124
125    build() {
126        Row() {
127        Column() {
128            Button(this.message)
129            .fontSize(50)
130            .fontWeight(FontWeight.Bold)
131            .onClick(() => {
132                const color : ArrayBuffer = new ArrayBuffer(96);
133                let opts: image.InitializationOptions = { alphaType: 0, editable: true, pixelFormat: 4, scaleMode: 1, size: { height: 4, width: 6 } }
134                image.createPixelMap(color, opts)
135                .then( (pixelmap : image.PixelMap) => {
136                    this._PixelMap = pixelmap;
137                    testNapi.testGetImageInfo(this._PixelMap);
138                    console.info("Test GetImageInfo success");
139
140                    testNapi.testAccessPixels(this._PixelMap);
141                    console.info("Test AccessPixels success");
142
143                    testNapi.testUnAccessPixels(this._PixelMap);
144                    console.info("Test UnAccessPixels success");
145                })
146            })
147        }
148        .width('100%')
149        }
150        .height('100%')
151    }
152    }
153    ```
154