some questions about CGWindowListCreateImage()

Subject: some questions about CGWindowListCreateImage()

Date: Thu, 27 Mar 2008 13:16:03 -0400

Delivered-to: email@hidden

Hello

I have successfully built some code based on the Son of Grab developer sample, but I have a few questions,

What I am looking to do (and optimize), is grabbing an arbitrary window image texture, and keep it on the GPU for further processing by my application.

I have a timer based system with grabs a current CGImageRef of the windowID Ive specified, but have noticed that any sort of decent framerate makes the WindowServer process really churn, which in turn kills the framerate in my main host application.

I am wondering/speculating if this is due to some sort of readback off the GPU when calling CGWindowListCreateImage(). Ive checked OpenGL Driver Monitor but am not certain what to look for to indicate readback is happening or that it is indeed causing a large bottleneck.

So, is it possible to keep the CGImageRef from CGWindowListCreateImage() on the GPU (from what I understand a CGIImageRef can live anywhere in main memory or in vram - is this assumption incorrect?), and if so, how do I do it!

The code I am using to pull in the window image and that is called at my timer is as follows:

-(void) windowToImage

{

if(currentWindowImage && currentWindowImage != nil)

{

CGImageRelease(currentWindowImage);

}

currentWindowImage = CGWindowListCreateImage(imageBounds, singleWindowListOptions, windowID, imageOptions);

CGImageRetain(currentWindowImage);

}

and then I simply expose currentWindowImage to the outside world, to be polled at whatever rate it should be (to decouple sampling from the window server from external processing of the resulting image).

-(id)getCurrentFrame

{

return currentWindowImage;

}

Does it make sense to use CGWindowListCreateImage, or should I be looking at the OpenGL Screen Capture example? I quite like CGWindowListCreateImage as it lets me capture obscured windows, and only the window, which im not certain I can do based on a sampling of the OpenGL Screen to Movie code. I have no problems being 10.5 only.

Thanks for any advice.

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