Android ApiDemos示例解析(76):Graphics->Regions

二维图形之间可以通过“加”，“减”，“交”，“异或”等逻辑运算构成新的图形。

本例使用了两个矩形通过“加”，“减”，“交”，“异或”构成组合后的图像，Region除支持矩形外，还可以使用Path来定义一个任意区域，然后再组合成复杂形状。可以参见Android简明开发教程十四：Context Menu 绘制几何图形 “梨子”。

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);
}