如何創建一個代表UIImage徑向部分的UIImage？

Question

給出下面的圖片，百分比說25％。我怎樣才能生成代表給定圖像徑向部分的25％的另一個UIImage？任何幫助是極大的讚賞。

輸入 輸出

- (UIImage *)radialPortion:(float)percent image:(UIImage *)image; 

Answer 1

- (UIImage *)radialPortion:(float)percent image:(UIImage *)image 
{ 
    CGSize size = image.size; 
    CGRect rect = {CGPointZero,size}; 
    UIGraphicsBeginImageContext(size); 
    CGFloat radius = MAX(size.width, size.height)/2; 
    UIBezierPath *path = [UIBezierPath bezierPath]; 
    CGPoint center = CGPointMake(size.width/2, size.height/2); 
    [path moveToPoint:center]; 
    [path addLineToPoint:CGPointMake(center.x, center.y-radius)]; 
    [path addArcWithCenter:center radius:radius startAngle:-M_PI_2 endAngle:-M_PI_2+M_PI*2*percent clockwise:1]; 
    [path closePath]; 
    [path addClip]; 
    [image drawInRect:rect]; 
    return UIGraphicsGetImageFromCurrentImageContext(); 
} 

注：代碼只是用於樣品圖像工作，可能不適用於其它圖像的工作。