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96 lines
3.3 KiB
96 lines
3.3 KiB
5 years ago
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Surface 跨进程传递原理
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---
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1. 怎么理解 surface，它是一块 buffer 嘛？
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2. 如果是，surface 跨进程传递怎么带上这个 buffer？
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3. 如果不是，那么 surface 跟 buffer 又是什么关系？
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4. surface 到底是怎么跨进程传递的？
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```java
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public class Surface implements Parcelable{
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long mNativeObject;
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private final Canvas mCanvas = new CompatibleCanvas();
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}
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public void writeToParcel(Parcel dest, int flags){
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synchronized(mLock){
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dest.writeString(mName);
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nativeWriteToParcel(mNativeObject, dest);
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}
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}
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public void readFromParcel(Parcel source){
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synchronized(mLock){
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mName = source.readString();
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setNativeObjectLocked(nativeReadFromParcel(mNativeObject, source));
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}
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}
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static void nativeWriteToParcel(JNIEnv* env, jclass clazz, jlong nativeObject, jobject parcelObj){
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Parcel* parcel = parcelForJavaObject(env, parcelObj);
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sp<Surface> self(reinterpert_cast<Surface*>(nativeObject));
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parcel->writeStrongBinder(IInterface::asBinder(self->getIGraphicBufferProducer()));
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}
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Parcel* parcelForJavaObject(JNIEnv* env, jobject obj){
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Parcel* p = env->GetLongField(obj, gParcelOffsets.mNativePtr);
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return p;
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}
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sp<IGraphicBufferProduct> getIGraphicBufferProducer() const{
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return mProducer;
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}
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static jlong nativeReadFromParcel(JNIEnv* env, jclass clazz, jlong nativeObject, jobject parcelObj){
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Parcel* parcel = parcelForJavaObject(env, parcelObj);
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sp<Surface> self(reinterpret_cast<Surface *>(nativeObject));
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sp<IBinder> binder(parcel->readStrongBinder());
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sp<IGraphicBufferProducer> gbp(interface_cast<IGraphicBufferProducer>(binder));
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sp<Surface> sur = new Surface(gbp, true);
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return jlong(sur.get());
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}
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```
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#### Activity 的 surface 是怎么跨进程传递的？
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```java
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private void performTraversals(){
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final View host = mView;
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if(mFirst){
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relayoutResult = relayoutWindow(params, ...);
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}
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}
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int relayoutWindow(WindowManager.LayoutParams params, ...){
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return mWindowSession.relayout(mWindow, ..., mSurface);
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}
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// WMS
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public int relayout(IWindow window, ..., Surface outSurface){
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int res = mService.relayoutWindow(this, window, ..., outSurface);
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return res;
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}
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public int relayoutWindow(Session session, ..., Surface outSurface){
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SurfaceControl surfaceControl = winAnimator.createSurfaceLocked();
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outSurface.copyForm(surfaceControl);
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}
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public void copyForm(SurfaceControl other){
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long surfaceControlPtr = other.mNativeObject;
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long newNativeObject = nativeCreateFromSurfaceControl(surfaceControlPtr);
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setNativeObjectLocked(newNativeObject);
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}
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jlong nativeCreateFromSurfaceControl(JNIEnv* env, jclass clazz, ...){
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sp<SurfaceControl> ctrl(reinterpret_cast<SurfaceControl *>(surfaceControlNativeObj));
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sp<Surface> surface(ctrl->getSurface());
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return reinterpret_cast<jlong>(surface.get());
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}
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sp<Surface> SurfaceControl::getSurface() const{
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if(mSurfaceData == 0){
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mSurfaceData = new Surface(mGraphicBufferProducer, false);
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}
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return mSurfaceData;
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}
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```
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#### 总结
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1. Surface 的本质是 GraphicBufferProducer，而不是 buffer
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2. Surface 跨进程传递，本质就是 GraphicBufferProducer 的传递
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Surface 不是一块 buffer，而是一个壳子，里面包含了一个能够生产 buffer 的 Binder 对象，也就是 GBP。Surface 跨进程传递，只是传递 GBP 对象。
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