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1、SurfaceView控件使用

1.1 Choreographer接受VSync信号

Choreographer是Android提供的一个获取VSync信号的通道。这里SurfaceView控件是主动上屏绘制，而一般应用如
WMS中Choreographer 配合 VSYNC 中断信号 中添加界面时从 ViewRootImpl 的 scheduleTraversals 方法开始，其内部通过 Choreographer 的 postCallback 将绘制任务添加到 Chorographer。

Choreographer.getInstance().postFrameCallback(new Choreographer.FrameCallback() {@Overridepublic void doFrame(long frameTimeNanos) {//当vsync信号来时会调用到这里mHandler.sendEmptyMessage(MyHandler.TAG_UPDATE_TEXT);Choreographer.getInstance().removeFrameCallback(this);Choreographer.getInstance().postFrameCallback(this);}});

1.2 自定义SurfaceView

• MySurfaceView构造函数中获取mSurfaceHolder = this.getHolder()，并设置SurfaceHolder.Callback
• 继承Runnable，Thread中运行，并Global.syncCondition.await(); 在这里等待vsync到来的通知消息
• 线程并发处理Lock和Condition：

public class Global {public static ReentrantLock lock = new ReentrantLock();public static Condition syncCondition = lock.newCondition();private Global() {}
}

• Choreographer#doFrame中Global.syncCondition.signal();通知另一条线程更新画面

com/xhbruce/ui/MySurfaceView.java

public class MySurfaceView extends SurfaceView implements SurfaceHolder.Callback, Runnable {private static String TAG = "MySurfaceView";private SurfaceHolder mSurfaceHolder;private int autoNum = 0;private Paint mPaint = new Paint();public MySurfaceView(Context context) {this(context, null);}public MySurfaceView(Context context, AttributeSet attrs) {this(context, attrs , 0);}public MySurfaceView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);mSurfaceHolder = this.getHolder();mSurfaceHolder.addCallback(this);Log.d(TAG, "MySurfaceView(3) holder=" + mSurfaceHolder.toString());}public MySurfaceView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {super(context, attrs, defStyleAttr, defStyleRes);mSurfaceHolder = this.getHolder();mSurfaceHolder.addCallback(this);Log.d(TAG, "MySurfaceView(4) holder=" + mSurfaceHolder.toString());}@Overridepublic void surfaceCreated(@NonNull SurfaceHolder holder) {Log.d(TAG, "surfaceCreated() holder=" + holder.toString());new Thread(this).start();
//        draw();//画蓝色或绿色}@Overridepublic void surfaceChanged(@NonNull SurfaceHolder holder, int format, int width, int height) {}@Overridepublic void surfaceDestroyed(@NonNull SurfaceHolder holder) {}@Overridepublic void run() {while (true) {Log.d(TAG, "run() autoNum=" + autoNum);Global.lock.lock();try {Global.syncCondition.await();//在这里等待vsync到来的通知消息} catch (InterruptedException e) {e.printStackTrace();} finally {Global.lock.unlock();}draw();//画蓝色或绿色}}private void draw() {Canvas mCanvas = null;try {mCanvas = mSurfaceHolder.lockCanvas();if (autoNum % 2 == 0) {mPaint.setColor(Color.BLUE);//如果为双数则画面画成蓝色} else {mPaint.setColor(Color.GREEN);//如果为单数则画面画成绿色}mCanvas.drawRect(0, 0, getRight(), getBottom(), mPaint);} catch (Exception e) {e.printStackTrace();} finally {if (mCanvas != null) {mSurfaceHolder.unlockCanvasAndPost(mCanvas);}}Log.d(TAG, "draw() autoNum=" + autoNum);autoNum++;//数字加1}
}

对应Activity和xml布局文件：
com/xhbruce/surfaceviewtest/MySurfaceViewTest.java

public class MySurfaceViewTest extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_my_surface_view_test);Choreographer.getInstance().postFrameCallback(new Choreographer.FrameCallback() {@Overridepublic void doFrame(long frameTimeNanos) {//当vsync信号来时会调用到这里Global.lock.lock();try {Global.syncCondition.signal();//通知另一条线程更新画面} catch (Exception e) {e.printStackTrace();} finally {Global.lock.unlock();}Choreographer.getInstance().removeFrameCallback(this);Choreographer.getInstance().postFrameCallback(this);}});}
}

layout/activity_my_surface_view_test.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".MySurfaceViewTest"><com.xhbruce.ui.MySurfaceViewandroid:layout_width="match_parent"android:layout_height="match_parent" />
</LinearLayout>

1.3 结果

2、SurfaceView获取画布并显示

• SurfaceHolder.lockCanvas()获得Canvas对象并锁定画布
• SurfaceHolder.unlockCanvasAndPost(Canvas canvas)结束锁定画图，并提交改变，将图形显示。

2.1 SurfaceHolder.lockCanvas()

Surface的lock方法最终调用到GraphicBufferProducer的dequeueBuffer函数获取一个Slot，如果Slot没有分配GraphicBuffer会在这时给它分配GraphicBuffer, 然后会返回一个带有BUFFER_NEEDS_REALLOCATION标记的flag, 应用侧看到这个flag后会通过requestBuffer和importBuffer接口把GraphicBuffer映射到自已的进程空间。

2.2 SurfaceHolder.unlockCanvasAndPost(Canvas canvas)

SurfaceView在更新视图时用到了两张Canvas，一张frontCanvas和一张backCanvas，每次实际显示的是frontCanvas，backCanvas存储的是上一次更改前的视图，当使用lockCanvas（）获取画布时，得到的实际上是backCanvas而不是正在显示的frontCanvas，之后你在获取到的backCanvas上绘制新视图，再unlockCanvasAndPost(Canvas canvas)此视图，那么上传的这张canvas将替换原来的frontCanvas作为新的frontCanvas，原来的frontCanvas将切换到后台作为backCanvas。