restoreCount() 将图层出栈

入栈时，后面所有的操作都会发生在这个图层中

出栈时，则会把图像绘制到上层Canvas上

@Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawColor(Color.WHITE); p.setColor(Color.BLUE); canvas.drawCircle(150, 150, 100, p); // 图一 canvas.saveLayerAlpha(0, 0, 400, 400, 127, LAYER_TYPE_NONE); // 图二 // canvas.saveLayerAlpha(0, 0, 400, 400, 255, LAYER_TYPE_NONE); p.setColor(Color.RED); canvas.drawCircle(200, 200, 100, p); canvas.restore(); }

图一，透明度为127时，为半透明状态

图二，透明度设置为255时，完全不透明

Android图像处理技巧 色彩矩阵分析

// ---- 施工中（8月2日--6日） ----

SurfaceView的使用

SurfaceView是为了解决View中执行操作逻辑太多出现卡顿的情况

SurfaceView和View的区别 SurfaceView的使用

创建SurfaceView

@Override public void surfaceCreated(SurfaceHolder surfaceHolder) { } @Override public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) { } @Override public void surfaceDestroyed(SurfaceHolder surfaceHolder) { } @Override public void run() { }

初始化SurfaceView

private SurfaceHolder mHolder; private Canvas mCanvas; private boolean mIsDrawing; private void init() { mHolder = getHolder(); mHolder.addCallback(this); }

使用SurfaceView

API 作用

lockCanvas() 获得当前Canvas对象

drawColor() 清屏

public class SurfaceViewDemo extends SurfaceView implements Runnable, SurfaceHolder.Callback { private SurfaceHolder mHolder; private Canvas mCanvas; private boolean mIsDrawing; // 子线程标志位 public SurfaceViewDemo(Context context) { super(context); initView(); } private void initView() { mHolder = getHolder(); mHolder.addCallback(this); setFocusable(true); setFocusableInTouchMode(true); this.setKeepScreenOn(true); // mHolder.setFormat(PixelFormat.OPAQUE); } @Override public void surfaceCreated(SurfaceHolder surfaceHolder) { mIsDrawing = true; new Thread(this).start(); } @Override public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) { } @Override public void surfaceDestroyed(SurfaceHolder surfaceHolder) { mIsDrawing = false; } @Override public void run() { while (mIsDrawing) { draws(); } } public void draws() { try { mCanvas = mHolder.lockCanvas(); } catch (Exception e) { } finally { if (mCanvas != null) { mHolder.unlockCanvasAndPost(mCanvas); } } } } SurfaceView实例 1. 正选曲线 @Override public void run() { while (mIsDrawing) { draws(); x += 1; y = (int) (100 * Math.sin(x * 2 * Math.PI/180) + 400); mPath.lineTo(x, y); } } private void draws() { try { mCanvas = mHolder.lockCanvas(); // Surface背景 mCanvas.drawColor(Color.WHITE); mCanvas.drawPath(mPath, mPaint); } catch (Exception e) { } finally { if (mCanvas != null) { mHolder.unlockCanvasAndPost(mCanvas); } } }