1# 预览流二次处理(C/C++)
2
3通过ImageReceiver创建预览输出，获取预览流实时数据，以供后续进行图像二次处理，比如应用可以对其添加滤镜算法等。
4
5## 开发步骤
6
7详细的API说明请参考[Camera API参考](../../reference/apis-camera-kit/_o_h___camera.md)。
8
91. 导入NDK接口，接口中提供了相机相关的属性和方法，导入方法如下。
10
11   ```c++
12    // 导入NDK接口头文件
13   #include <cstdlib>
14   #include <hilog/log.h>
15   #include <memory>
16   #include <multimedia/image_framework/image/image_native.h>
17   #include <multimedia/image_framework/image/image_receiver_native.h>
18   #include "ohcamera/camera.h"
19   #include "ohcamera/camera_input.h"
20   #include "ohcamera/capture_session.h"
21   #include "ohcamera/preview_output.h"
22   #include "ohcamera/camera_manager.h"
23   ```
24
252. 在CMake脚本中链接相关动态库。
26
27   ```txt
28   target_link_libraries(entry PUBLIC
29       libace_napi.z.so
30       libhilog_ndk.z.so
31       libohimage.so
32       libimage_receiver.so
33       libnative_image.so
34       libohcamera.so
35       libnative_buffer.so
36   )
37   ```
38
393. 初始化图片接收器[ImageReceiver](../image/image-receiver-c.md)实例，获取SurfaceId。
40
41   通过image的OH_ImageReceiverNative_Create方法创建OH_ImageReceiverNative实例，再通过实例的OH_ImageReceiverNative_GetReceivingSurfaceId方法获取SurfaceId。
42
43   ```c++
44   void InitImageReceiver() {
45       OH_ImageReceiverOptions *options = nullptr;
46       // 注意捕获错误码处理异常及对象判空，当前示例仅展示调用流程
47       // 设置图片参数
48       Image_ErrorCode errCode = OH_ImageReceiverOptions_Create(&options);
49       Image_Size imgSize;
50       imgSize.width = 1080; // 创建预览流的宽
51       imgSize.height = 1080; // 创建预览流的高
52       int32_t capacity = 8; // BufferQueue里最大Image数量，推荐填写8
53       errCode = OH_ImageReceiverOptions_SetSize(options, imgSize);
54       errCode = OH_ImageReceiverOptions_SetCapacity(options, capacity);
55       // 创建OH_ImageReceiverNative对象
56       OH_ImageReceiverNative *receiver = nullptr;
57       errCode = OH_ImageReceiverNative_Create(options, &receiver);
58       // 获取OH_ImageReceiverNative对象的SurfaceId
59       uint64_t receiverSurfaceID = 0;
60       errCode = OH_ImageReceiverNative_GetReceivingSurfaceId(receiver, &receiverSurfaceID);
61       OH_LOG_INFO(LOG_APP, "receiver surfaceID:%{public}%llu", receiverSurfaceID);
62   }
63   ```
64
654. 通过上一步获取到的SurfaceId创建预览流，参考[预览(C/C++)](./native-camera-preview.md)步骤4。
66
675. 创建会话，使能会话，参考[会话管理(C/C++)](./native-camera-session-management.md)。
68
696. 注册ImageReceiver图片接收器的回调，监听获取每帧上报图像内容。
70
71   ```c++
72   OH_ImageReceiverNative *receiver; // 步骤3创建的实例
73
74   // 图像回调函数，参考媒体/Image Kit（图片处理服务）
75   static void OnCallback(OH_ImageReceiverNative *receiver) {
76       OH_LOG_INFO(LOG_APP, "ImageReceiverNativeCTest buffer available.");
77       // 注意捕获错误码处理异常及对象判空，当前示例仅展示调用流程
78       OH_ImageNative *image = nullptr;
79       // 从bufferQueue中获取图像
80       Image_ErrorCode errCode = OH_ImageReceiverNative_ReadNextImage(receiver, &image);
81       // 读取图像宽高
82       Image_Size size;
83       errCode = OH_ImageNative_GetImageSize(image, &size);
84       OH_LOG_INFO(LOG_APP, "OH_ImageNative_GetImageSize errCode:%{public}d width:%{public}d height:%{public}d", errCode,
85           size.width, size.height);
86
87       // 获取图像ComponentType
88       size_t typeSize = 0;
89       OH_ImageNative_GetComponentTypes(image, nullptr, &typeSize);
90       uint32_t* types = new uint32_t[typeSize];
91       OH_ImageNative_GetComponentTypes(image, &types, &typeSize);
92       uint32_t component = types[0];
93       // 获取图像buffer
94       OH_NativeBuffer *imageBuffer = nullptr;
95       errCode = OH_ImageNative_GetByteBuffer(image, component, &imageBuffer);
96       size_t bufferSize = 0;
97       errCode = OH_ImageNative_GetBufferSize(image, component, &bufferSize);
98       OH_LOG_INFO(LOG_APP, "ImageReceiverNativeCTest buffer component: %{public}d size:%{public}zu", component, bufferSize);
99       // 获取图像行距
100       int32_t stride = 0;
101       errCode = OH_ImageNative_GetRowStride(image, component, &stride);
102       OH_LOG_INFO(LOG_APP, "ImageReceiverNativeCTest buffer stride：%{public}d.", stride);
103       void* srcVir = nullptr;
104       OH_NativeBuffer_Map(imageBuffer, &srcVir);
105       uint8_t* srcBuffer = static_cast<uint8_t*>(srcVir);
106       // 判断行距与预览流宽是否一致，如不一致，需要考虑stride对读取buffer的影响
107       if (stride == size.width) {
108           // 传给其他不需要stride的接口处理
109       } else {
110           // 传给其他支持stride的接口处理，或去除stride数据
111           // 去除stride数据示例:将byteBuffer中的数据去除stride，拷贝得到新的dstBuffer数据
112           size_t dstBufferSize = size.width * size.height * 1.5; // 相机预览流返回NV21格式
113           std::unique_ptr<uint8_t[]> dstBuffer = std::make_unique<uint8_t[]>(dstBufferSize);
114           uint8_t *dstPtr = dstBuffer.get();
115           for (int j = 0; j < size.height * 1.5; j++) {
116               memcpy(dstPtr, srcBuffer, size.width);
117               dstPtr += size.width;
118               srcBuffer += stride;
119           }
120           // 传给其他不需要stride的接口处理
121       }
122       // 释放资源
123       OH_NativeBuffer_Unmap(imageBuffer); // 释放buffer,保证bufferQueue正常轮转
124       errCode = OH_ImageNative_Release(image);
125	   delete[] types;
126   }
127
128   void OnImageReceiver() {
129       // 注册图像回调事件，监听每帧上报的图像
130       Image_ErrorCode errCode = OH_ImageReceiverNative_On(receiver, OnCallback);
131   }
132   ```