根据顶部图像的alpha /透明度混合两个uiimages [英] blend two uiimages based on alpha/transparency of top image

问题描述

我正在尝试将背景与前景图像混合，其中前景图像是带有线条的透明图像。

I'm trying to blend a background with a foreground image, where the foreground image is a transparent image with lines on it.

我正在尝试这样做这样。

I am trying to do it this way.

UIGraphicsBeginImageContext(CGSizeMake(320, 480));
CGContextRef context = UIGraphicsGetCurrentContext();   

// create rect that fills screen
CGRect bounds = CGRectMake( 0,0, 320, 480);

// This is my bkgnd image
CGContextDrawImage(context, bounds, [UIImage imageNamed:@"bkgnd.jpg"].CGImage);

CGContextSetBlendMode(context, kCGBlendModeSourceIn);

// This is my image to blend in
CGContextDrawImage(context, bounds, [UIImage imageNamed:@"over.png"].CGImage);

UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

UIImageWriteToSavedPhotosAlbum(outputImage, self, nil, nil);
// clean up drawing environment
//
UIGraphicsEndImageContext();

但似乎不起作用。

任何建议都将受到赞赏。

Any suggestions will be appreciated.

推荐答案

这就是我在我的应用程序中所做的，类似于Tyler的 - 但没有 UIImageView ：

This is what I've done in my app, similar to Tyler's - but without the UIImageView:

UIImage *bottomImage = [UIImage imageNamed:@"bottom.png"];
UIImage *image = [UIImage imageNamed:@"top.png"];

CGSize newSize = CGSizeMake(width, height);
UIGraphicsBeginImageContext( newSize );

// Use existing opacity as is
[bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
// Apply supplied opacity
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.8];

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

如果图片已经具有不透明度，则无需进行设置（如 bottomImage ）否则你可以设置它（与 image 一样）。

If the image already has opacity, you do not need to set it (as in bottomImage) otherwise you can set it (as with image).

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