如何向 UIImage 或 UIImageView 或 UIView 添加外部发光

我想添加褪色的阴影/外发光到UIImage/UIImageView/UIView但我知道没有Core Graphics根本不。

Edit:请帮忙！！

采用 Cirrostratus 概述的方法，保留其缓存副本，然后在拖动时应用变换来更改图像的大小和/或位置。

（警告，这不是功能/测试代码，但应该可以帮助您入门）

-(UIImage*)addGlowToImage:(UIImage*)imageInput;
{
    CGRect newSize = imageInput.bounds;
    CGImageRef theImage = imageInput.CGImage;

    // expand the size to handle the "glow"
    newSize.size.width += 6.0;
    newSize.size.height += 6.0;
    UIGraphicsBeginImageContext(newSize);
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    CGContextBeginTransparencyLayerWithRect(ctx, newSize, NULL);
    CGContextClearRect(ctx, newSize);

    // you can repeat this process to build glow.
    CGContextDrawImage(ctx, newSize, theImage); 
    CGContextSetAlpha(ctx, 0.2);  

    CGContextEndTransparencyLayer(ctx);

    // draw the original image into the context, offset to be centered;
    CGRect centerRect = inputImage.bounds;
    centerRect.origin.x += 3.0;
    centerRect.origin.y += 3.0;
    CGContextDrawImage(ctx, centerRect, theImage);

    result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return result;
}

然后在你的方法中，在缩放时你会做类似的事情：

// assumes UIImage *cachedImage = [self addGlowToImage:origImage]; has been called already.
// assumes ivars for scale exists

    CGRect newRect = cachedImage.bounds;
    newRect.size.width += scale;
    newRect.size.height += scale;

    [cachedImage drawInRect:newRect];  // image will be scaled to fill destination rectangle.

一定要看看苹果文档。一个好的起点是Quartz 2D 编程指南 http://developer.apple.com/iphone/library/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/Introduction/Introduction.html.