代码让UIImage具有渐变效果

做一个UIImage的category，直接上代码：

- (UIImage *) imageWithBackgroundColor:(UIColor *)bgColor shadeAlpha1:(CGFloat)alpha1 shadeAlpha2:(CGFloat)alpha2 shadeAlpha3:(CGFloat)alpha3 shadowColor:(UIColor *)shadowColor shadowOffset:(CGSize)shadowOffset shadowBlur:(CGFloat)shadowBlur { UIImage *image = self; CGColorRef cgColor = [bgColor CGColor]; CGColorRef cgShadowColor = [shadowColor CGColor]; CGFloat components[16] = {1,1,1,alpha1,1,1,1,alpha1,1,1,1,alpha2,1,1,1,alpha3}; CGFloat locations[4] = {0,0.5,0.6,1}; CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGGradientRef colorGradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, (size_t)4); CGRect contextRect; contextRect.origin.x = 0.0f; contextRect.origin.y = 0.0f; contextRect.size = [image size]; //contextRect.size = CGSizeMake([image size].width+5,[image size].height+5); // Retrieve source image and begin image context UIImage *itemImage = image; CGSize itemImageSize = [itemImage size]; CGPoint itemImagePosition; itemImagePosition.x = ceilf((contextRect.size.width - itemImageSize.width) / 2); itemImagePosition.y = ceilf((contextRect.size.height - itemImageSize.height) / 2); UIGraphicsBeginImageContext(contextRect.size); CGContextRef c = UIGraphicsGetCurrentContext(); // Setup shadow CGContextSetShadowWithColor(c, shadowOffset, shadowBlur, cgShadowColor); // Setup transparency layer and clip to mask CGContextBeginTransparencyLayer(c, NULL); CGContextScaleCTM(c, 1.0, -1.0); CGContextClipToMask(c, CGRectMake(itemImagePosition.x, -itemImagePosition.y, itemImageSize.width, -itemImageSize.height), [itemImage CGImage]); // Fill and end the transparency layer CGContextSetFillColorWithColor(c, cgColor); contextRect.size.height = -contextRect.size.height; CGContextFillRect(c, contextRect); CGContextDrawLinearGradient(c, colorGradient,CGPointZero,CGPointMake(contextRect.size.width*1.0/4.0,contextRect.size.height),0); CGContextEndTransparencyLayer(c); //CGPointMake(contextRect.size.width*3.0/4.0, 0) // Set selected image and end context UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); CGColorSpaceRelease(colorSpace); CGGradientRelease(colorGradient); return resultImage;} 

用法如下：

UIImage *niceImage = [[UIImage imageNamed:@"image_name"] imageWithBackgroundColor:[UIColor colorWithRed:41.0/255.0 green:147.0/255.0 blue:239.0/255.0 alpha:1.0] shadeAlpha1:0.6 shadeAlpha2:0.0 shadeAlpha3:0.4 shadowColor:[UIColor blackColor] shadowOffset:CGSizeMake(0.0f, -1.0f) shadowBlur:3.0];