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];