android SurfaceView绘制 重新学习--切图clipRect详解

解释都在代码注释中：

 public class SampleView extends View {
     private Paint mPaint;
     private Path mPath;

     public SampleView(Context context) {
         super(context);
         setFocusable(true);

         mPaint = new Paint();
         mPaint.setAntiAlias(true);
         mPaint.setStrokeWidth(6);
         mPaint.setTextSize(16);
         mPaint.setTextAlign(Paint.Align.RIGHT);

         mPath = new Path();
     }

     private void drawScene(Canvas canvas) {
         canvas.clipRect(0, 0, 100, 100);

         canvas.drawColor(Color.WHITE);

         mPaint.setColor(Color.RED);
         canvas.drawLine(0, 0, 100, 100, mPaint);

         mPaint.setColor(Color.GREEN);
         canvas.drawCircle(30, 70, 30, mPaint);

         mPaint.setColor(Color.BLUE);
         canvas.drawText("Clipping", 100, 30, mPaint);
     }

     @Override
     protected void onDraw(Canvas canvas) {
         canvas.drawColor(Color.GRAY);
         canvas.save();
         canvas.translate(10, 10);
         drawScene(canvas);
         canvas.restore();

         // Region.Op.DIFFERENCE B-A
         canvas.save();
         canvas.translate(160, 10);
         canvas.clipRect(10, 10, 90, 90); // B
         canvas.clipRect(30, 30, 70, 70, Region.Op.DIFFERENCE); // A
         drawScene(canvas);
         canvas.restore();

         // 这里因为在3.0以上的硬件上开启了硬件加速,会有问题.
         // Region.Op.REPLACE 不论A和B的集合状况，B的范围将全部进行显示，如果和A有交集，则将覆盖A的交集范围
 //        canvas.save();
 //        canvas.translate(10, 160);
 //        mPath.reset();
 //        canvas.clipPath(mPath); // B
 //        mPath.addCircle(50, 50, 50, Path.Direction.CCW);
 //        canvas.clipPath(mPath, Region.Op.REPLACE);// A
 //        drawScene(canvas);
 //        canvas.restore();

         // Region.Op.UNION AB并集范围
         canvas.save();
         canvas.translate(160, 160);
         canvas.clipRect(0, 0, 60, 60);// B
         canvas.clipRect(40, 40, 100, 100, Region.Op.UNION);// A
         drawScene(canvas);
         canvas.restore();

         // Region.Op.XOR 异或，去掉AB相交的部分
         canvas.save();
         canvas.translate(10, 310);
         canvas.clipRect(40, 40, 100, 100); // B
         canvas.clipRect(0, 0, 60, 60, Region.Op.XOR); // A
         drawScene(canvas);
         canvas.restore();

         // Region.Op.REVERSE_DIFFERENCE A-B
         canvas.save();
         canvas.translate(160, 310);
         canvas.clipRect(0, 0, 60, 60); // B
         canvas.clipRect(40, 40, 100, 100, Region.Op.REVERSE_DIFFERENCE);// A
         drawScene(canvas);
         canvas.restore();
     }
 }

这个在游戏中还是很常用的。

关于硬件加速的问题，http://developer.android.com/guide/topics/graphics/hardware-accel.html#controlling

谷歌文档说的很清楚。