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    1. 在xxx.ets中添加一个XComponent组件。
46        ```ts
47        XComponent({ id: 'xcomponentId', type: 'surface', libraryname: 'entry'})
48            .width(360)
49            .height(360)
50        ```
51    2. 在 native c++ 层获取 NativeXComponent。
52        ```c++
53        napi_value exportInstance = nullptr;
54        // 用来解析出被wrap了NativeXComponent指针的属性
55        napi_get_named_property(env, exports, OH_NATIVE_XCOMPONENT_OBJ, &exportInstance);
56        OH_NativeXComponent *nativeXComponent = nullptr;
57        // 通过napi_unwrap接口，解析出NativeXComponent的实例指针
58        napi_unwrap(env, exportInstance, reinterpret_cast<void**>(&nativeXComponent));
59        // 获取XComponentId
60        char idStr[OH_XCOMPONENT_ID_LEN_MAX + 1] = {};
61        uint64_t idSize = OH_XCOMPONENT_ID_LEN_MAX + 1;
62        OH_NativeXComponent_GetXComponentId(nativeXComponent, idStr, &idSize);
63        ```
64    3. 定义 OH_NativeXComponent_Callback。
65        ```c++
66        // 定义回调函数
67        void OnSurfaceCreatedCB(OH_NativeXComponent* component, void* window)
68        {
69            // 可获取 OHNativeWindow 实例
70            OHNativeWindow* nativeWindow = static_cast<OHNativeWindow*>(window);
71            // 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xcompnent析构的情况，
72            // 则需要通过OH_NativeWindow_NativeObjectReference和OH_NativeWindow_NativeObjectUnreference对window进行
73            // 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。
74        }
75        void OnSurfaceChangedCB(OH_NativeXComponent* component, void* window)
76        {
77            // 可获取 OHNativeWindow 实例
78            OHNativeWindow* nativeWindow = static_cast<OHNativeWindow*>(window);
79            // ...
80        }
81        void OnSurfaceDestroyedCB(OH_NativeXComponent* component, void* window)
82        {
83            // 可获取 OHNativeWindow 实例
84            OHNativeWindow* nativeWindow = static_cast<OHNativeWindow*>(window);
85            // 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，
86            // 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。
87        }
88        void DispatchTouchEventCB(OH_NativeXComponent* component, void* window)
89        {
90            // 可获取 OHNativeWindow 实例
91            OHNativeWindow* nativeWindow = static_cast<OHNativeWindow*>(window);
92            // ...
93        }
94        ```
95        ```c++
96        // 初始化 OH_NativeXComponent_Callback
97        OH_NativeXComponent_Callback callback;
98        callback.OnSurfaceCreated = OnSurfaceCreatedCB;
99        callback.OnSurfaceChanged = OnSurfaceChangedCB;
100        callback.OnSurfaceDestroyed = OnSurfaceDestroyedCB;
101        callback.DispatchTouchEvent = DispatchTouchEventCB;
102        ```
103   4. 将 OH_NativeXComponent_Callback 注册给 NativeXComponent。
104        ```c++
105        // 注册回调函数
106        OH_NativeXComponent_RegisterCallback(nativeXComponent, &callback);
107        ```
108
1092. **设置OHNativeWindowBuffer的属性**。使用`OH_NativeWindow_NativeWindowHandleOpt`设置`OHNativeWindowBuffer`的属性。
110    ```c++
111    // 设置 OHNativeWindowBuffer 的宽高
112    int32_t code = SET_BUFFER_GEOMETRY;
113    int32_t width = 0x100;
114    int32_t height = 0x100;
115    // 这里的nativeWindow是从上一步骤中的回调函数中获得的
116    int32_t ret = OH_NativeWindow_NativeWindowHandleOpt(nativeWindow, code, width, height);
117    ```
118
1193. **从图形队列申请OHNativeWindowBuffer**。
120    ```c++
121    OHNativeWindowBuffer* buffer = nullptr;
122    int releaseFenceFd = -1;
123    // 通过 OH_NativeWindow_NativeWindowRequestBuffer 获取 OHNativeWindowBuffer 实例
124    ret = OH_NativeWindow_NativeWindowRequestBuffer(nativeWindow, &buffer, &releaseFenceFd);
125    if (ret != 0 || buffer == nullptr) {
126        return;
127    }
128    // 通过 OH_NativeWindow_GetBufferHandleFromNative 获取 buffer 的 handle
129    BufferHandle* bufferHandle = OH_NativeWindow_GetBufferHandleFromNative(buffer);
130    ```
131
1324. **内存映射mmap**。
133    ```c++
134    #include <sys/mman.h>
135
136    // 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
137    // 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
138    void* mappedAddr = mmap(bufferHandle->virAddr, bufferHandle->size, PROT_READ | PROT_WRITE, MAP_SHARED, bufferHandle->fd, 0);
139    if (mappedAddr == MAP_FAILED) {
140        // mmap failed
141    }
142    ```
143
1445. **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。**
145    ```c++
146    int retCode = -1;
147    uint32_t timeout = 3000;
148    if (releaseFenceFd != -1) {
149        struct pollfd pollfds = {0};
150        pollfds.fd = releaseFenceFd;
151        pollfds.events = POLLIN;
152        do {
153            retCode = poll(&pollfds, 1, timeout);
154        } while (retCode == -1 && (errno == EINTR || errno == EAGAIN));
155        close(releaseFenceFd); // 防止fd泄漏
156    }
157
158    static uint32_t value = 0x00;
159    value++;
160    uint32_t *pixel = static_cast<uint32_t *>(mappedAddr); // 使用mmap获取到的地址来访问内存
161    for (uint32_t x = 0; x < width; x++) {
162        for (uint32_t y = 0;  y < height; y++) {
163            *pixel++ = value;
164        }
165    }
166    ```
167
1686. **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。**
169    ```c++
170    // 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。
171    Region region{nullptr, 0};
172    int acquireFenceFd = -1;
173    // 通过OH_NativeWindow_NativeWindowFlushBuffer 提交给消费者使用，例如：显示在屏幕上。
174    OH_NativeWindow_NativeWindowFlushBuffer(nativeWindow, buffer, acquireFenceFd, region);
175    ```
1767. **取消内存映射munmap**。
177    ```c++
178    // 内存使用完记得去掉内存映射
179    int result = munmap(mappedAddr, bufferHandle->size);
180    if (result == -1) {
181        // munmap failed
182    }
183    ```
184
185## 相关实例
186
187针对NativeWindow的开发，有以下相关实例可供参考：
188
189- [NativeWindow（API11）](https://gitee.com/openharmony/applications_app_samples/tree/master/code/BasicFeature/Native/NdkNativeWindow)