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。