CGContextDrawRadialGradient用于非圆形发光 [英] CGContextDrawRadialGradient For Non-Circular Glow

问题描述

我可以使用 CGContextDrawRadialGradient 制作一个球体，该球体的alpha渐变为 UIColor.clearColor ，

I'm able to use CGContextDrawRadialGradient to make a sphere that does an alpha fade to UIColor.clearColor and it works.

但是，我正在尝试做这种事情：

However, I'm trying to do this type of thing:

同时在周围放置一些战略性区域有趣的效果（类似于战略性场所的LED背光），我很想获得真正的发光。 如何在 drawRect 的圆角矩形周围绘制辉光？

While placing some strategic spheres around makes for an interesting effect (similar to LED backlights in strategic places), I would love to get a true glow. How can I draw a glow around a rounded rectangle in drawRect?

推荐答案

您可以使用 CGContextSetShadowWithColor 在任何路径周围创建发光效果，但是您无法精确控制外观。特别是，默认阴影相当浅：

You can create a glow effect around any path using CGContextSetShadowWithColor, but you don't get precise control over the appearance. In particular, the default shadow is fairly light:

我知道使它更暗的唯一方法是在自身上再次绘制它：

And the only way I know of to make it darker is to draw it again over itself:

不是最佳的

这些图像是由以下 drawRect 生成的：

Those images were generated by the following drawRect:

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGMutablePathRef path = CGPathCreateMutable();

    int padding = 20;
    CGPathMoveToPoint(path, NULL, padding, padding);
    CGPathAddLineToPoint(path, NULL, rect.size.width - padding, rect.size.height / 2);
    CGPathAddLineToPoint(path, NULL, padding, rect.size.height - padding);

    CGContextSetShadowWithColor(context, CGSizeZero, 20, UIColor.redColor.CGColor);
    CGContextSetFillColorWithColor(context, UIColor.blueColor.CGColor);

    CGContextAddPath(context, path);
    CGContextFillPath(context);
    // CGContextAddPath(context, path);
    // CGContextFillPath(context);

    CGPathRelease(path);
}

要记住的一件事是渲染模糊阴影相当昂贵，取决于是否多久重新绘制一次视图，可能是问题，也可能不是问题。如果阴影不需要设置动画，请考虑将其渲染到 UIImage 一次，然后在 UIImageView 。

One thing to bear in mind is that rendering fuzzy shadows is fairly expensive, which may or may not be a problem depending on how often your views are redrawn. If the shadows don't need to animate, consider rendering them to a UIImage once and just displaying the result in a UIImageView.

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