如何在Quard 2D使用clipping的办法绘制。

draw-arrow-with-clipping.mm

- (void)drawRect:(CGRect)rect
{
    // assume the background color is white
    
    CGContextRef con = UIGraphicsGetCurrentContext();
    
    // punch triangle hole in context clipping region
    CGContextMoveToPoint(con, 90, 100);
    CGContextAddLineToPoint(con, 100, 90);
    CGContextAddLineToPoint(con, 110, 100);
    CGContextClosePath(con);
    CGContextAddRect(con, CGContextGetClipBoundingBox(con));
    CGContextEOClip(con);
    
    // draw the vertical line, add its shape to the clipping region
    CGContextMoveToPoint(con, 100, 100);
    CGContextAddLineToPoint(con, 100, 19);
    CGContextSetLineWidth(con, 20);
    CGContextStrokePath(con);
    
    // draw the red triangle, the point of the arrow
    CGContextSetFillColorWithColor(con, [[UIColor redColor] CGColor]);
    CGContextMoveToPoint(con, 80, 25);
    CGContextAddLineToPoint(con, 100, 0);
    CGContextAddLineToPoint(con, 120, 25);
    CGContextFillPath(con);
}