canvas的save和restore

/**
* 在画布的 左下角画圆，
* 中间画向右箭头 ：旋转画布后再画
* 右上角画圆：画布旋转为原始方向后再画
* @param canvas
*/
private void canvasTest(Canvas canvas) {
int width = 200;
int height = 200;
int radius = 10;
int centerX = radius;
int centerY = height - radius;
Paint paint = new Paint();
//画做左下角的圆
paint.setStyle(Style.FILL);
paint.setColor(Color.BLUE);
paint.setAntiAlias(true);
canvas.drawCircle(centerX, centerY, radius, paint);

canvas.save();
//画三角形
canvas.rotate(90, width/2, height/2);   //以画布中心为旋转点
//		canvas.translate(0, -30);
//		canvas.scale(1.2f, 1.2f, width/2, height/2);

paint.setColor(Color.RED);
paint.setStyle(Style.STROKE);
paint.setStrokeWidth(4);
//左线、右线、中线， 把旋转后的当做新画布，但x, y 的坐标仍是原来方向的，但画出的图是旋转后的
//可以想象为先在原始画布上画，画好后旋转
canvas.drawLine(width/2, 0, 0, height/2, paint);
canvas.drawLine(width/2, 0, width, height/2, paint);
canvas.drawLine(width/2, 0, width/2, height, paint);
canvas.restore();  //如果不加这一行，那么下面的那个右上角的圆是 旋转后的画布的右上角，而非原始画布的右上角位置

//右上角画个圆
int cx2 = width - radius;
int cy2 = radius;
paint.setStyle(Style.FILL);
paint.setColor(Color.RED);
canvas.drawCircle(cx2, cy2, radius, paint);
}