Canvas的save和restore

int px = getMeasuredWidth();
int py = getMeasuredWidth();
 
// Draw background
canvas.drawRect(0, 0, px, py, backgroundPaint);
 
canvas.save();
canvas.rotate(90, px/2, py/2);                
 
// Draw up arrow
canvas.drawLine(px / 2, 0, 0, py / 2, linePaint);                
canvas.drawLine(px / 2, 0, px, py / 2, linePaint);
canvas.drawLine(px / 2, 0, px / 2, py, linePaint);
 
canvas.restore();
 
// Draw circle
canvas.drawCircle(px - 10, py - 10, 10, linePaint);