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1# NativeWindow开发指导 (C/C++)
2
3## 场景介绍
4
5NativeWindow是**本地平台化窗口**，表示图形队列的生产者端。开发者可以通过`NativeWindow`接口进行申请和提交`Buffer`，配置`Buffer`属性信息。
6针对NativeWindow，常见的开发场景如下：
7
8* 通过`NativeWindow`提供的Native API接口申请图形`Buffer`，并将生产图形内容写入图形`Buffer`，最终提交`Buffer`到图形队列。
9* 在适配EGL层的`eglswapbuffer`接口时，进行申请和提交`Buffer`。
10
11## 接口说明
12
13| 接口名 | 描述 |
14| -------- | -------- |
15| OH_NativeWindow_NativeWindowRequestBuffer (OHNativeWindow \*window, OHNativeWindowBuffer \*\*buffer, int \*fenceFd) | 通过OHNativeWindow对象申请一块OHNativeWindowBuffer，用以内容生产。 |
16| OH_NativeWindow_NativeWindowFlushBuffer (OHNativeWindow \*window, OHNativeWindowBuffer \*buffer, int fenceFd, Region region) | 通过OHNativeWindow将生产好内容的OHNativeWindowBuffer放回到Buffer队列中，用以内容消费。 |
17| OH_NativeWindow_NativeWindowHandleOpt (OHNativeWindow \*window, int code,...) | 设置/获取OHNativeWindow的属性，包括设置/获取宽高、内容格式等。 |
18
19详细的接口说明请参考[native_window](../reference/apis-arkgraphics2d/_native_window.md)。
20
21## 开发步骤
22
23以下步骤描述了如何使用`NativeWindow`提供的Native API接口，申请图形`Buffer`，并将生产图形内容写入图形`Buffer`后，最终提交`Buffer`到图形队列。
24
25**添加动态链接库**
26
27CMakeLists.txt中添加以下lib。
28```txt
29libace_ndk.z.so
30libnative_window.so
31```
32
33**头文件**
34```c++
35#include <sys/poll.h>
36#include <sys/mman.h>
37#include <unistd.h>
38#include <ace/xcomponent/native_interface_xcomponent.h>
39#include <native_window/external_window.h>
40```
41
421. 获取OHNativeWindow实例。
43
44    可在[`OH_NativeXComponent_Callback`](../reference/apis-arkui/_o_h___native_x_component___callback.md)提供的接口中获取OHNativeWindow，下面提供一份代码示例。XComponent模块的具体使用方法请参考[XComponent开发指导](../ui/napi-xcomponent-guidelines.md)。
45
46    1. 在xxx.ets中添加一个XComponent组件。
47
48        ```ts
49        XComponent({ id: 'xcomponentId', type: 'surface', libraryname: 'entry'})
50            .width(360)
51            .height(360)
52        ```
53    2. 在 native c++ 层获取 NativeXComponent。
54
55        ```c++
56        napi_value exportInstance = nullptr;
57        // 用来解析出被wrap了NativeXComponent指针的属性
58        napi_get_named_property(env, exports, OH_NATIVE_XCOMPONENT_OBJ, &exportInstance);
59        OH_NativeXComponent *nativeXComponent = nullptr;
60        // 通过napi_unwrap接口，解析出NativeXComponent的实例指针
61        napi_unwrap(env, exportInstance, reinterpret_cast<void**>(&nativeXComponent));
62        // 获取XComponentId
63        char idStr[OH_XCOMPONENT_ID_LEN_MAX + 1] = {};
64        uint64_t idSize = OH_XCOMPONENT_ID_LEN_MAX + 1;
65        OH_NativeXComponent_GetXComponentId(nativeXComponent, idStr, &idSize);
66        ```
67    3. 定义 OH_NativeXComponent_Callback。
68
69        ```c++
70        // 定义回调函数
71        void OnSurfaceCreatedCB(OH_NativeXComponent* component, void* window)
72        {
73            // 可获取 OHNativeWindow 实例
74            OHNativeWindow* nativeWindow = static_cast<OHNativeWindow*>(window);
75            // 此回调触发后，window默认引用计数会设置为1，若存在并发使用了window相关的接口和xcomponent析构的情况，
76            // 则需要通过OH_NativeWindow_NativeObjectReference和OH_NativeWindow_NativeObjectUnreference对window进行
77            // 手动引用计数加1和减1，防止xcomponent析构后，并发调用window相关接口触发野指针或空指针的崩溃。
78        }
79        void OnSurfaceChangedCB(OH_NativeXComponent* component, void* window)
80        {
81            // 可获取 OHNativeWindow 实例
82            OHNativeWindow* nativeWindow = static_cast<OHNativeWindow*>(window);
83            // ...
84        }
85        void OnSurfaceDestroyedCB(OH_NativeXComponent* component, void* window)
86        {
87            // 可获取 OHNativeWindow 实例
88            OHNativeWindow* nativeWindow = static_cast<OHNativeWindow*>(window);
89            // 此回调触发后，会将window进行引用计数减1的操作，当window的应用计数为0后，会触发window的析构，
90            // window析构后，不可再通过window进行接口调用，否则可能会触发野指针或空指针的崩溃。
91        }
92        void DispatchTouchEventCB(OH_NativeXComponent* component, void* window)
93        {
94            // 可获取 OHNativeWindow 实例
95            OHNativeWindow* nativeWindow = static_cast<OHNativeWindow*>(window);
96            // ...
97        }
98        ```
99
100        ```c++
101        // 初始化 OH_NativeXComponent_Callback
102        OH_NativeXComponent_Callback callback;
103        callback.OnSurfaceCreated = OnSurfaceCreatedCB;
104        callback.OnSurfaceChanged = OnSurfaceChangedCB;
105        callback.OnSurfaceDestroyed = OnSurfaceDestroyedCB;
106        callback.DispatchTouchEvent = DispatchTouchEventCB;
107        ```
108
109   4. 将OH_NativeXComponent_Callback 注册给 NativeXComponent。
110
111        ```c++
112        // 注册回调函数
113        OH_NativeXComponent_RegisterCallback(nativeXComponent, &callback);
114        ```
115
1162. 设置OHNativeWindowBuffer的属性。使用`OH_NativeWindow_NativeWindowHandleOpt`设置`OHNativeWindowBuffer`的属性。
117
118    ```c++
119    // 设置 OHNativeWindowBuffer 的宽高
120    int32_t code = SET_BUFFER_GEOMETRY;
121    int32_t width = 0x100;
122    int32_t height = 0x100;
123    // 这里的nativeWindow是从上一步骤中的回调函数中获得的
124    int32_t ret = OH_NativeWindow_NativeWindowHandleOpt(nativeWindow, code, width, height);
125    ```
126
1273. 从图形队列申请OHNativeWindowBuffer。
128
129    ```c++
130    OHNativeWindowBuffer* buffer = nullptr;
131    int releaseFenceFd = -1;
132    // 通过 OH_NativeWindow_NativeWindowRequestBuffer 获取 OHNativeWindowBuffer 实例
133    ret = OH_NativeWindow_NativeWindowRequestBuffer(nativeWindow, &buffer, &releaseFenceFd);
134    if (ret != 0 || buffer == nullptr) {
135        return;
136    }
137    // 通过 OH_NativeWindow_GetBufferHandleFromNative 获取 buffer 的 handle
138    BufferHandle* bufferHandle = OH_NativeWindow_GetBufferHandleFromNative(buffer);
139    ```
140
1414. 内存映射mmap。
142
143    ```c++
144    #include <sys/mman.h>
145
146    // 使用内存映射函数mmap将bufferHandle对应的共享内存映射到用户空间，可以通过映射出来的虚拟地址向bufferHandle中写入图像数据
147    // bufferHandle->virAddr是bufferHandle在共享内存中的起始地址，bufferHandle->size是bufferHandle在共享内存中的内存占用大小
148    void* mappedAddr = mmap(bufferHandle->virAddr, bufferHandle->size, PROT_READ | PROT_WRITE, MAP_SHARED, bufferHandle->fd, 0);
149    if (mappedAddr == MAP_FAILED) {
150        // mmap failed
151    }
152    ```
153
1545. 将生产的内容写入OHNativeWindowBuffer，在这之前需要等待releaseFenceFd可用（注意releaseFenceFd不等于-1才需要调用poll）。如果没有等待releaseFenceFd事件的数据可用（POLLIN），则可能造成花屏、裂屏、HEBC（High Efficiency Bandwidth Compression，高效带宽压缩） fault等问题。releaseFenceFd是消费者进程创建的一个文件句柄，代表消费者消费buffer完毕，buffer可读，生产者可以开始填充buffer内容。
155
156    ```c++
157    int retCode = -1;
158    uint32_t timeout = 3000;
159    if (releaseFenceFd != -1) {
160        struct pollfd pollfds = {0};
161        pollfds.fd = releaseFenceFd;
162        pollfds.events = POLLIN;
163        do {
164            retCode = poll(&pollfds, 1, timeout);
165        } while (retCode == -1 && (errno == EINTR || errno == EAGAIN));
166        close(releaseFenceFd); // 防止fd泄漏
167    }
168
169    static uint32_t value = 0x00;
170    value++;
171    uint32_t *pixel = static_cast<uint32_t *>(mappedAddr); // 使用mmap获取到的地址来访问内存
172    for (uint32_t x = 0; x < width; x++) {
173        for (uint32_t y = 0;  y < height; y++) {
174            *pixel++ = value;
175        }
176    }
177    ```
178
1796. 提交OHNativeWindowBuffer到图形队列。请注意OH_NativeWindow_NativeWindowFlushBuffer接口的acquireFenceFd不可以和OH_NativeWindow_NativeWindowRequestBuffer接口获取的releaseFenceFd相同，acquireFenceFd可传入默认值-1。acquireFenceFd是生产者需要传入的文件句柄，消费者获取到buffer后可根据生产者传入的acquireFenceFd决定何时去渲染并上屏buffer内容。
180
181    ```c++
182    // 设置刷新区域，如果Region中的Rect为nullptr,或者rectNumber为0，则认为OHNativeWindowBuffer全部有内容更改。
183    Region region{nullptr, 0};
184    int acquireFenceFd = -1;
185    // 通过OH_NativeWindow_NativeWindowFlushBuffer 提交给消费者使用，例如：显示在屏幕上。
186    OH_NativeWindow_NativeWindowFlushBuffer(nativeWindow, buffer, acquireFenceFd, region);
187    ```
188
1897. 取消内存映射munmap。
190
191    ```c++
192    // 内存使用完记得去掉内存映射
193    int result = munmap(mappedAddr, bufferHandle->size);
194    if (result == -1) {
195        // munmap failed
196    }
197    ```
198
199## 相关实例
200
201针对NativeWindow的开发，有以下相关实例可供参考：
202
203- [NativeWindow（API11）](https://gitee.com/openharmony/applications_app_samples/tree/master/code/BasicFeature/Native/NdkNativeWindow)