Android ApiDemos示例解析(58):Graphics->Clipping
本例介绍Canvas的裁剪功能。
Canvas提供了ClipPath, ClipRect, ClipRegion 等方法来裁剪，通过Path, Rect ,Region 的不同组合，Android几乎可以支持任意现状的裁剪区域。
android.graphics包中定义了Point, Rect, Path, Region 这几种几何形状，Path可以为有圆弧，椭圆，二次曲线，三次曲线，线段，矩形等基本几何图形或是由这些基本几何图形组合而成，Path可以为开放或是闭合曲线。Rect提供了定义矩形的简洁方法。Region则支持通过区域的“加”，“减”，“并”，“异或”等逻辑运算由多个Region组合而成。Region.Op定义了Region支持的区域间运算种类。
Clipping 介绍有Region运算来为Canvs定义剪裁区域后，同一幅图最后显示的效果。canvas.save();和canvas.restore();用于保存和恢复Canvas的状态属性。
drawScene定义了绘图的内容：一条红线，一个绿圆，和“Clipping”文字
[java]
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);
}
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);
}剪裁区域为两个矩形相减：
[java]
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(160, 10);
canvas.clipRect(10, 10, 90, 90);
canvas.clipRect(30, 30, 70, 70, Region.Op.DIFFERENCE);
drawScene(canvas);
canvas.restore();剪裁区域为一个圆
[java]
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(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();剪裁区域为两个矩形的并集：
[java]
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(160, 160);
canvas.clipRect(0, 0, 60, 60);
canvas.clipRect(40, 40, 100, 100, Region.Op.UNION);
drawScene(canvas);
canvas.restore();剪裁区域为两个矩形的异或集：
[java]
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(10, 310);
canvas.clipRect(0, 0, 60, 60);
canvas.clipRect(40, 40, 100, 100, Region.Op.XOR);
drawScene(canvas);
canvas.restore();最后一个为两个矩形的逆向差集：
[java]
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();
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();
作者：mapdigit
补充：移动开发 , Android ,
