绘制一个多边形，并用背景图像填充它

initWithPatternImage

colorWithPatternImage

UIBezierPath

CGContextStrokeLineSegments

- (void)drawRect:(CGRect)rect
{
    UIColor *color = [UIColor colorWithPatternImage:myPatternImage];
    [color set];

    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:p1];
    [path addLineToPoint:p2];
    [path addLineToPoint:p3];
    [path addLineToPoint:p4];
    [path closePath]; // Implicitly does a line between p4 and p1
    [path fill]; // If you want it filled, or...
    [path stroke]; // ...if you want to draw the outline.
}

[path setLineWidth:5];