canvas 的cliprect（）实现画布剪切DEMO

canvas 的cliprect（）能够对画布实现剪切，显示需要的可见区域，除了此区域之外的地方其任何内容都不可见，这个区域可以是矩形也可以是圆。

这个demo简单用了一张图片在画布中使用cliprect方法剪切了一部分，需要注意的是要用到 save（）和restore（）两个成对出现的方法！其实对剪切的操作就是在这两个方法之间进行的，简单的说就是在cliprect设置了可见区域后，在这个可见区域内进行的操作能够保留下来，不在这个区域内操作的东西通过restore（）方法就把它“清除掉了”

public class MSurfaceView extends SurfaceView implements Callback, Runnable{
    
    private SurfaceHolder holder;
    private Paint paint, paintFont;
    private Thread mThread;
    private Canvas canvas;
    private boolean state;
    private int x, y;
    private int window_x, window_y;
    private final static int MAX_TIME = 80;
    private Bitmap mBitmap, backBitmap;
    
    public MSurfaceView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
        holder = this.getHolder();
        paint = new Paint();
        paintFont = new Paint();
        paint.setColor(Color.BLUE);
        paintFont.setColor(Color.WHITE);
        holder.addCallback(this);
        setFocusable(true);
    }

    @Override
    public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
        // TODO Auto-generated method stub
        Log.v("tag", "surfacechanged");
    }

    @Override
    public void surfaceCreated(SurfaceHolder arg0) {
        // TODO Auto-generated method stub
        Log.v("tag", "surfacecreated");
        window_x = this.getWidth();
        window_y = this.getHeight();
        state = true;
        mThread = new Thread(this);
        mThread.start();

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder arg0) {
        // TODO Auto-generated method stub
        Log.v("tag", "surfacedestoryed");
        state = false;
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        x = (int)event.getX();
        y = (int)event.getY();
        return true;
    }
    public void mDraw(){
        try {
            canvas = holder.lockCanvas();
//            if (canvas != null) {
//                backBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.okc);
//                canvas.drawBitmap(backBitmap, 0, 0, paint);
                canvas.drawRGB(0, 0, 0);
                mBitmap = BitmapFactory.decodeResource(this.getResources(), R.drawable.ic_launcher);
                canvas.drawBitmap(mBitmap, x, y, paint);
                Log.v("tag", "绘制位图");
                canvas.save();
                canvas.clipRect(0, 0, 200, 200);
                backBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.okc);
                canvas.drawBitmap(backBitmap, 0, 0, paint);
//                canvas.drawRect(0, 0, this.getWidth(), this.getHeight(), paint);
//                canvas.translate(10, 10);
//                canvas.drawBitmap(mBitmap, 50, 50, paint);
                canvas.restore();
//                canvas.drawCircle(x, y, getradius(), paint);
//                canvas.drawText("坐标值：" + x, 30, 30, paintFont); 
//                canvas.drawText("坐标值：" + y, 40, 40, paintFont); 
//            }
        } catch (Exception e) {
            // TODO: handle exception
        }finally{
            if (canvas != null) {
                holder.unlockCanvasAndPost(canvas);
            }
        }
    }
    private int getradius(){
         int r = (int)(Math.random()*30);
         return r;
    }


    @Override
    public void run() {
        // TODO Auto-generated method stub
        while(state){
            long start = System.currentTimeMillis();
            mDraw();
            long end = System.currentTimeMillis();
            if ((end - start) < MAX_TIME) {
                try {
                    Thread.sleep(MAX_TIME - (end - start));
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }

}

用MainActivity.java显示当前的view：

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(new MSurfaceView(this));
    }
    
    
}

第一张时剪切后的效果，第二张是原始图片

哈哈哈 图片有点太大了 没管那么多

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下面再通过另外一种方式实现画布剪切，这次剪切一个圆形区域，使用path：

canvas.save();
                Path path = new Path();
                path.addCircle(40, 50, 30, Direction.CCW);
                canvas.clipPath(path);
                backBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.okc);
                canvas.drawBitmap(backBitmap, 0, 0 ,paint);
canvas.restore();

首先实例化path，然后添加一个指定大小的circle并将这个circle作为我们所要的可见区域，再在屏幕上面绘制我们的图片，然后使用restore方法，“清除”掉我们绘制时候没有在可见区域内的操作，最后看到的效果如下：