将PNG图像绘制到混合模式操作的图形上下文中 [英] Drawing a PNG Image Into a Graphics Context for Blending Mode Manipulation

问题描述

我需要在 CGContext 中绘制一系列PNG，以便将它们混合在一起：

I need to draw a series of PNGs into a CGContext so I can blend them together:

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(context, kCGBlendModeOverlay);

目前我的应用程序基于将每个图像绘制为UIImageView并将其添加为子视图到视图文件： [self addSubview：someImageView] ...但是这不允许混合模式操作，对吗？

Currently I have my app working based on just drawing each image as a UIImageView and adding them as a subview to the view file via: [self addSubview:someImageView] ...but this doesn't allow for blending mode manipulation, right?

目前UIImageView的vars是通过以下方式分配的：

Currently the UIImageView vars are being assigned via:

someImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image-name.png"]];

所以我试着用没有运气的替换这些：

So I've tried replacing those with either of these with no luck:

[[UIImage imageNamed:@"image-name.png"] drawInRect:rect blendMode:kCGBlendModeOverlay alpha:1.0];

，这需要一个 CGImage 不知道如何使用PNG：

and this one needs a CGImage which I'm not sure how to make with the PNGs:

CGContextDrawImage(context, rect, someCGImage);

那么我缺少什么？这些不是由任何互动触发，他们只需要加载/绘制应用程序加载时。

So what am I missing? These aren't being triggered by any interaction, they just need to load/draw when the app loads.

感谢任何线索。 ：）

推荐答案

您不需要使用UIImageView。
相反，在调用 UIGraphicsBeginImageContext 和 UIGraphicsEndImageContext 之间加上你的绘图。

You don't need to be using UIImageViews. Instead, bracket your drawing between calls to UIGraphicsBeginImageContext and UIGraphicsEndImageContext.

例如（代码未尝试）：

UIImage* uiimage = [UIImage imageNamed:@"image-name.png"];
UIImage* uiimage2 = [UIImage imageNamed:@"other-image-name.png"];

CGSize size = uiimage.size; 

UIGraphicsBeginImageContext(size);

[uiimage drawAtPoint:CGPointZero blendMode:kCGBlendModeOverlay alpha:1.0];
[uiimage2 drawAtPoint:CGPointZero blendMode:kCGBlendModeOverlay alpha:1.0];

UIImage* blendedImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

如果要使用CG调用，请调用：

If you want to use CG calls, call:

CGContextRef context = UIGraphicsGetCurrentContext();

获取上下文引用。

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