Region.Op

二維圖形之間能夠經過「加」，「減」，「交」，「異或」等邏輯運算構成新的圖形。

本例使用了兩個矩形經過「加」，「減」，「交」，「異或」構成組合後的圖像，Region除支持矩形外，還可使用Path來定義一個任意區域，而後再組合成複雜形狀。能夠參見Android簡明開發教程十四：Context Menu 繪製幾何圖形 「梨子」。

[java] 
canvas.save(); 
canvas.translate(0, 140); 
drawRgn(canvas, Color.RED, "Union", Region.Op.UNION); 
canvas.restore(); 
  
canvas.save(); 
canvas.translate(0, 280); 
drawRgn(canvas, Color.BLUE, "Xor", Region.Op.XOR); 
canvas.restore(); 
  
canvas.save(); 
canvas.translate(160, 140); 
drawRgn(canvas, Color.GREEN, "Difference", Region.Op.DIFFERENCE); 
canvas.restore(); 
  
canvas.save(); 
canvas.translate(160, 280); 
drawRgn(canvas, Color.WHITE, "Intersect", Region.Op.INTERSECT); 
canvas.restore(); 
  
... 
  
private void drawRgn(Canvas canvas, int color, 
 String str, Region.Op op) { 
 if (str != null) { 
 mPaint.setColor(Color.BLACK); 
 canvas.drawText(str, 80, 24, mPaint); 
 } 
  
 Region rgn = new Region(); 
 rgn.set(mRect1); 
 rgn.op(mRect2, op); 
  
 mPaint.setColor(color); 
 RegionIterator iter = new RegionIterator(rgn); 
 Rect r = new Rect(); 
  
 canvas.translate(0, 30); 
 mPaint.setColor(color); 
 while (iter.next(r)) { 
 canvas.drawRect(r, mPaint); 
 } 
 drawOriginalRects(canvas, 0x80); 
} 

canvas.save();
canvas.translate(0, 140);
drawRgn(canvas, Color.RED, "Union", Region.Op.UNION);
canvas.restore();
 
canvas.save();
canvas.translate(0, 280);
drawRgn(canvas, Color.BLUE, "Xor", Region.Op.XOR);
canvas.restore();
 
canvas.save();
canvas.translate(160, 140);
drawRgn(canvas, Color.GREEN, "Difference", Region.Op.DIFFERENCE);
canvas.restore();
 
canvas.save();
canvas.translate(160, 280);
drawRgn(canvas, Color.WHITE, "Intersect", Region.Op.INTERSECT);
canvas.restore();
 
...
 
private void drawRgn(Canvas canvas, int color,
 String str, Region.Op op) {
 if (str != null) {
 mPaint.setColor(Color.BLACK);
 canvas.drawText(str, 80, 24, mPaint);
 }
 
 Region rgn = new Region();
 rgn.set(mRect1);
 rgn.op(mRect2, op);
 
 mPaint.setColor(color);
 RegionIterator iter = new RegionIterator(rgn);
 Rect r = new Rect();
 
 canvas.translate(0, 30);
 mPaint.setColor(color);
 while (iter.next(r)) {
 canvas.drawRect(r, mPaint);
 }
 drawOriginalRects(canvas, 0x80);
}

 

做者：mapdigit