如何将包含核心动画层的视图渲染为位图? [英] How do I render a view which contains Core Animation layers to a bitmap?

问题描述

我正在使用 NSView 来托管多个 Core Animation CALayer 对象.我想要做的是抓取视图当前状态的快照作为位图图像.

I am using an NSView to host several Core Animation CALayer objects. What I want to be able to do is grab a snapshot of the view's current state as a bitmap image.

对于普通的 NSView 使用类似这样的东西，这相对简单:

This is relatively simple with a normal NSView using something like this:

void ClearBitmapImageRep(NSBitmapImageRep* bitmap) {
    unsigned char* bitmapData = [bitmap bitmapData];
    if (bitmapData != NULL)
        bzero(bitmapData, [bitmap bytesPerRow] * [bitmap pixelsHigh]);
}

@implementation NSView (Additions)
- (NSBitmapImageRep*)bitmapImageRepInRect:(NSRect)rect
{
    NSBitmapImageRep* imageRep = [self bitmapImageRepForCachingDisplayInRect:rect];
    ClearBitmapImageRep(imageRep);
    [self cacheDisplayInRect:rect toBitmapImageRep:imageRep];
    return imageRep;
}
@end

但是，当我使用此代码时，不会渲染核心动画层.

However, when I use this code, the Core Animation layers are not rendered.

我已经调查了 CARenderer，因为它似乎可以满足我的需求，但是我无法让它渲染我现有的图层树.我尝试了以下方法:

I have investigated CARenderer, as it appears to do what I need, however I cannot get it to render my existing layer tree. I tried the following:

NSOpenGLPixelFormatAttribute att[] = 
{
    NSOpenGLPFAWindow,
    NSOpenGLPFADoubleBuffer,
    NSOpenGLPFAColorSize, 24,
    NSOpenGLPFAAlphaSize, 8,
    NSOpenGLPFADepthSize, 24,
    NSOpenGLPFANoRecovery,
    NSOpenGLPFAAccelerated,
    0
};

NSOpenGLPixelFormat *pixelFormat = [[NSOpenGLPixelFormat alloc] initWithAttributes:att];
NSOpenGLView* openGLView = [[NSOpenGLView alloc] initWithFrame:[self frame] pixelFormat:pixelFormat];
NSOpenGLContext* oglctx = [openGLView openGLContext];

CARenderer* renderer = [CARenderer rendererWithCGLContext:[oglctx CGLContextObj] options:nil];
renderer.layer = myContentLayer;
[renderer render];
NSBitmapImageRep* bitmap = [oglView bitmapImageRepInRect:[oglView bounds]];

但是，当我这样做时，我得到了一个例外:

However, when I do this I get an exception:

CAContextInvalidLayer -- layer 已经附加到上下文

我猜这一定是因为层树托管在我的 NSView 中，因此附加到其上下文.我不明白如何从 NSView 中分离图层树以将其呈现为位图，在这种情况下创建重复的图层树并非易事.

I'm guessing that this must be because the layer tree is hosted in my NSView and therefore attached to its context. I don't understand how I can detach the layer tree from the NSView in order to render it to a bitmap, and it's non-trivial in this case to create a duplicate layer tree.

是否有其他方法可以让 CALayer 渲染到位图?我在任何地方都找不到任何用于执行此操作的示例代码，实际上我根本找不到 CARenderer 的任何示例代码.

Is there some other way to get the CALayers to render to a bitmap? I can't find any sample code anywhere for doing this, in fact I can't find any sample code for CARenderer at all.

推荐答案

关于录制 Core Animations 的Cocoa 是我的女朋友"有一篇很棒的帖子.作者将整个动画捕捉到电影中，但您可以使用他抓取单个帧的部分.
跳转到本文的获取当前帧"部分:
http://www.cimgf.com/2009/02/03/record-your-core-animation-animation/

There is a great post on "Cocoa is my girlfriend" about recording Core Animations. The author captures the whole animation into a movie, but you could use the part where he grabs a single frame.
Jump to the "Obtaining the Current Frame" section in this article:
http://www.cimgf.com/2009/02/03/record-your-core-animation-animation/

基本思想是:

• 创建一个 CGContext
• 使用CALayer 的 renderInContext:
• 从上下文(使用CGBitmapContextCreateImage 和NSBitmapImageRep 的 initWithCGImage)

更新:
我刚刚读到 renderInContext: 方法不支持 Mac OS X 10.5 中的所有类型的层.它不适用于以下图层类:

Update:
I just read, that the renderInContext: method does not support all kind of layers in Mac OS X 10.5. It does not work for the following layers classes:

• QCCompositionLayer
• CAOpenGL层
• QTMovieLayer

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