【读书笔记《Android游戏编程之从零开始》】15.游戏开发基础（剪切区域）

    private void myDraw() {
        try {
            canvas = sfh.lockCanvas();
            if (canvas != null) {    
                //通过图片资源生成一张Bitmap 位图
                Bitmap bmp = BitmapFactory.decodeResource(this.getResources(), R.drawable.pic01);
                
                canvas.save();
                canvas.drawText("原图：", 20, 20, paint);
                canvas.drawBitmap(bmp, 20, 30,paint);
                canvas.restore();
                
                canvas.save();
                canvas.drawText("通过坐标，设置矩形可视区域：", 20, 320, paint);
                /**
                 * 为画布设置矩形可视区域
                 * 第一、二个参数为可视区域的左上角
                 * 第三、四个参数为可视区域的右下角
                 */
                canvas.clipRect(20,330,bmp.getWidth()+20,bmp.getHeight()/2+330);
                canvas.drawBitmap(bmp, 20, 330,paint);
                canvas.restore();
                
                canvas.save();
                canvas.drawText("利用 Path 来设置可视区域的形状,这里为圆形可视区域：", 20, 620, paint);
                Path path = new Path();
                path.addCircle(20+bmp.getWidth()/2, 630+bmp.getHeight()/2, bmp.getWidth()/2, Direction.CCW);
                /**
                 * 为画布设置可视区域
                 * 参数：Path实例
                 * 利用Paht 可以为位图设置任何需要的可视区域，这里是设置一个圆形可视区域。
                 */
                canvas.clipPath(path);
                canvas.drawBitmap(bmp, 20, 630, paint);
                canvas.restore();
                
                canvas.save();
                canvas.drawText("利用 Region 来对画布设置可视区域：", 20, 920, paint);
                Region region = new Region();
                //区域块全部显示
                region.op(new Rect(20,930,120,1030), Region.Op.UNION);
                //不显示交集区域
                region.op(new Rect(50,930,100,1080), Region.Op.XOR);
                canvas.clipRegion(region);
                canvas.drawBitmap(bmp, 20, 930, paint);
                canvas.restore();
                }
        } catch (Exception e) {
        } finally {
            if (canvas != null) {
                sfh.unlockCanvasAndPost(canvas);
            }
        }
    }