如何向 UIImage 或 UIImageView 或 UIView 添加外发光

How do I add an outer glow to a UIImage or UIImageView or UIView(如何向 UIImage 或 UIImageView 或 UIView 添加外发光)

问题描述

我想为 UIImage/UIImageView/UIView 添加 FADED 阴影/外发光，但我不知道 Core Graphics 完全没有.

I want to add a FADED shadow/outer glow to a UIImage/UIImageView/UIView but I know no Core Graphics at all.

请帮忙！！

推荐答案

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

Take the approach outlined by Cirrostratus, keep a cached copy of it, and then apply a transform to change the size and/or position of the image while dragging.

(警告，这不是功能/测试代码，但应该让你开始)

(warning, this is not functional/tested code, but should get you started)

-(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;
}

然后在您的方法中，在缩放时您会执行以下操作:

Then in your method while scaling you would do something like:

// 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.Quartz 2D Programming Guide.

Definitely take a look at the apple docs. A good starting place is the Quartz 2D Programming Guide.

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