iPhone-UIImage蒙版和CopyImageAndAddAlphaChannel函数

问题描述

我正在尝试创建一个拼图游戏，我需要对UIImage进行遮罩以获得拼图.

I am trying to create a jigsaw puzzle and I need to mask the UIImages to obtain the puzzle pieces.

我不知道如何屏蔽JPG图片，因为据我了解它没有Alpha通道.谁能帮我这个?JPG位于在线服务器上，无法将其下载为PNG.

I don't understand how can I mask a JPG picture because as I understand it doesn't have an alpha channel. Can anyone help me with this?The JPGs are on an online server and there is no way to download them as PNG.

还有一件事，我在Apple文档中的任何地方都找不到此功能:"CopyImageAndAddAlphaChannel".它甚至存在.我在一些论坛上找到了一些参考资料，但毫无进展.

And one more thing, I can’t find this function anywhere on the Apple documentation:"CopyImageAndAddAlphaChannel". Does it even exist. I found a few references on some forums but nothing strait forward.

非常感谢，安德烈(Andrei)

Thanks a lot,Andrei

推荐答案

找到了答案.这是此功能，它适用于不带alpha通道的JPG和PNG(我已经测试过了:)):

Found the answer. Here is the function, it works for JPG and PNG without alpha channel (I have tested it :)):

CGImageRef imageRef = self.CGImage;
size_t width = CGImageGetWidth(imageRef);
size_t height = CGImageGetHeight(imageRef);


CGContextRef offscreenContext = CGBitmapContextCreate(NULL,
                                                      width,
                                                      height,
                                                      8,
                                                      0,
                                                      CGImageGetColorSpace(imageRef),
                                                      kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedFirst);


CGContextDrawImage(offscreenContext, CGRectMake(0, 0, width, height), imageRef);
CGImageRef imageRefWithAlpha = CGBitmapContextCreateImage(offscreenContext);
UIImage *imageWithAlpha = [UIImage imageWithCGImage:imageRefWithAlpha];


CGContextRelease(offscreenContext);
CGImageRelease(imageRefWithAlpha);

return imageWithAlpha;

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