如何设置 UIImage 的不透明度/alpha? [英] How to set the opacity/alpha of a UIImage?

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本文介绍了如何设置 UIImage 的不透明度/alpha?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我知道你可以用 UIImageView 做到这一点,但它可以用在 UIImage 上吗?我想让 UIImageView 的动画图像数组属性成为相同图像但具有不同不透明度的数组.想法?

I know you can do this with a UIImageView, but can it be done to a UIImage? I want to have the animation images array property of a UIImageView to be an array of the same image but with different opacities. Thoughts?

推荐答案

我只需要这样做,但认为 Steven 的解决方案会很慢.这应该有希望使用图形硬件.在 UIImage 上创建一个类别:

I just needed to do this, but thought Steven's solution would be slow. This should hopefully use graphics HW. Create a category on UIImage:

- (UIImage *)imageByApplyingAlpha:(CGFloat) alpha {
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0f);

    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGRect area = CGRectMake(0, 0, self.size.width, self.size.height);

    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -area.size.height);

    CGContextSetBlendMode(ctx, kCGBlendModeMultiply);

    CGContextSetAlpha(ctx, alpha);

    CGContextDrawImage(ctx, area, self.CGImage);

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return newImage;
}

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