Android Camera 代码阅读: Preview过程

1. 主要 功能是什么？

2. 代码在哪些文件上？

3. 流程画出来

4. 如果修改和移植？

5. 如何优化？

6. 能否用新的机制，更好的方案来取代它？

以startPreview为例，追踪代码：

App: Java层代码

android/packages/apps/src/com/android/camera.java

// This can only be called by UI Thread.
private void startPreview() {
if (mPaused) {
return;
}
SurfaceTexture st = mUI.getSurfaceTexture();      

    Log.v(TAG, "startPreview");                   
    mCameraDevice.startPreview();   //这个CameraProxy是从哪里蹦出来的？  framework层的？            
    mFocusManager.onPreviewStarted();             
    onPreviewStarted();                           
                                                      

JNI 层：

android/frameworks/base/core/java/android/hardware/Camera.java

注册底层cpp实现的相应函数，这样上层java就可以通过JNI调用native提供的对于函数

static JNINativeMethod camMethods[] = {
{ "getNumberOfCameras",
"()I",
(void *)android_hardware_Camera_getNumberOfCameras },
{ "_getCameraInfo",
"(ILandroid/hardware/Camera$CameraInfo;)V",
(void*)android_hardware_Camera_getCameraInfo },
{ "native_setup",
"(Ljava/lang/Object;ILjava/lang/String;)V",
(void*)android_hardware_Camera_native_setup },
{ "native_release",
"()V",
(void*)android_hardware_Camera_release },
{ "setPreviewDisplay",
"(Landroid/view/Surface;)V",
(void *)android_hardware_Camera_setPreviewDisplay },
{ "setPreviewTexture",
"(Landroid/graphics/SurfaceTexture;)V",
(void *)android_hardware_Camera_setPreviewTexture },
{ "setPreviewCallbackSurface",
"(Landroid/view/Surface;)V",
(void *)android_hardware_Camera_setPreviewCallbackSurface },
{ "startPreview",
"()V",
(void *)android_hardware_Camera_startPreview },
{ "_stopPreview",
"()V",
(void *)android_hardware_Camera_stopPreview },   

。。。。。。

    // Register native functions                                                
    return AndroidRuntime::registerNativeMethods(env, "android/hardware/Camera",
                                              camMethods, NELEM(camMethods));   
}                                                                               

typedef struct {
const char* name; //JAVA函数名
const char* signature;
void* fnPtr;     //指向C函数
} JNINativeMethod;

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