Android Clipping

轉自：https://blog.csdn.net/gaomatrix/article/details/6532144

[java] view plain copy
public class Clipping extends Activity {  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(new SampleView(this));  
    }  
      
    private static 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();  
              
            canvas.save();  
            canvas.translate(160, 10);  
            canvas.clipRect(10, 10, 90, 90);  
            canvas.clipRect(30, 30, 70, 70, Region.Op.DIFFERENCE);  
            drawScene(canvas);  
            canvas.restore();  
              
            canvas.save();  
            canvas.translate(10, 160);  
            mPath.reset();  
            canvas.clipPath(mPath); // makes the clip empty  
            mPath.addCircle(50, 50, 50, Path.Direction.CCW);  
            canvas.clipPath(mPath, Region.Op.REPLACE);  
            drawScene(canvas);  
            canvas.restore();  
              
            canvas.save();  
            canvas.translate(160, 160);  
            canvas.clipRect(0, 0, 60, 60);  
            canvas.clipRect(40, 40, 100, 100, Region.Op.UNION);  
            drawScene(canvas);  
            canvas.restore();  
              
            canvas.save();  
            canvas.translate(10, 310);  
            canvas.clipRect(0, 0, 60, 60);  
            canvas.clipRect(40, 40, 100, 100, Region.Op.XOR);  
            drawScene(canvas);  
            canvas.restore();  
              
            canvas.save();  
            canvas.translate(160, 310);  
            canvas.clipRect(0, 0, 60, 60);  
            canvas.clipRect(40, 40, 100, 100, Region.Op.REVERSE_DIFFERENCE);  
            drawScene(canvas);  
            canvas.restore();  
        }  
    }  
}  

//DIFFERENCE是第一次不同於第二次的部分顯示出來 
//REPLACE是顯示第二次的 
//REVERSE_DIFFERENCE 是第二次不同於第一次的部分顯示 

//INTERSECT交集顯示 
//UNION全部顯示 
//XOR補集 就是全集的減去交集生育部分顯示

 

canvas.translate(float dx, float dy)方法的解釋：

和j2me的translate用法一樣，作用就是移動原點，默認的原點（0，0）是在屏幕左上角的，你可以通過translate（x，y）把點（x，y）作爲原點

 

 

Canvas提供了ClipPath, ClipRect, ClipRegion 等方法來裁剪，通過Path, Rect ,Region 的不同組合，Android幾乎可以支持任意現狀的裁剪區域。

 

android.graphics包中定義了Point, Rect, Path, Region 這幾種幾何形狀，Path可以爲有圓弧，橢圓，二次曲線，三次曲線，線段，矩形等基本幾何圖形或是由這些基本幾何圖形組合而成，Path可以爲開放或是閉合曲線。Rect提供了定義矩形的簡潔方法。Region則支持通過區域的“加”，“減”，“並”，“異或”等邏輯運算由多個Region組合而成。Region.Op定義了Region支持的區域間運算種類。

 

Clipping 介紹有Region運算來爲Canvs定義剪裁區域後，同一幅圖最後顯示的效果。canvas.save();和canvas.restore();用於保存和恢復Canvas的狀態屬性。