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teichgraf's picture

AccessViolationException using GL.CopyTexImage2D

Posted Tuesday, 11 March, 2008 - 09:32 by teichgraf in

It's me again with another annoying question ;)

In my little demo I use Two-Pass-Rendering:
In the first step I render everything to the back-buffer.
After that, the buffer is copied to a texture with GL.CopyTexImage2D.
In the second step the copied texture is rendered on a big quad.

My problem:
Everytime the demo is running and I swith to the desktop (pressing [Windows] + [D]), I get an
AccessViolationException: "Attemped to read or write from protected memory"
from GL.CopyTexImage2D.

This also happens If I swith to another graphics application.

static int TEX_SIZE = 512;
GL.BindTexture(TextureTarget.Texture2d, texRender);
GL.CopyTexImage2D(TextureTarget.Texture2d, 0, PixelInternalFormat.Rgba, 0, 0, TEX_SIZE, TEX_SIZE, 0);
// ^^^ The exception occurs here

[EDIT]
I added an example of the Two-Pass-Rendering mentioned above, using the QuickStart-Project. Check out the RenderFrame-method. While executing switch to the windows desktop (e.g. [Windows] + [D]).
[/EDIT]

AttachmentSize
QuickStart_2PassRender.zip9.26 KB
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the Fiddler's picture

Re: AccessViolationException using GL.CopyTexImage2D

Posted Tuesday, 11 March, 2008 - 09:53 by the Fiddler

Ok, can you try the following? In the resize event, add an if statement to avoid passing negative values to GL.Viewport:

if (e.Width > 0 && e.Height > 0)
    GL.Viewport(...);

There is a known issue where GameWindow.Resize reports a negative height when it is iconified (only affects Windows, not Linux).

Does this solve the crash?

the Fiddler's picture

Re: AccessViolationException using GL.CopyTexImage2D

Posted Tuesday, 11 March, 2008 - 10:03 by the Fiddler

Also, check this:
If any of the pixels within the specified rectangle of the current GL_READ_BUFFER are outside the window associated with the current rendering context, then the values obtained for those pixels are undefined.
[source: CopyTexImage2D manpage]

You should check if the current viewport is equal to, or larger than TEX_SIZE before calling the function.

teichgraf's picture

Re: AccessViolationException using GL.CopyTexImage2D

Posted Tuesday, 11 March, 2008 - 10:22 by teichgraf

Thanks for your ideas. But they don't solve the problem.

I added an example of the Two-Pass-Rendering in the initial post (see above).

the Fiddler's picture

Re: AccessViolationException using GL.CopyTexImage2D

Posted Tuesday, 11 March, 2008 - 10:52 by the Fiddler

Ok, I can confirm the problem under Windows/Mesa, but it doesn't occur under Windows/Microsoft or Linux/flgrx combinations. I haven't tried under hardware accelerated Windows/Ati or software accelerated Linux/Mesa drivers yet.

It is possible that iconified windows should be treated differently from normal windows (e.g. the rendering should be suspended). I'll check the MSDN and cook up a solution or workaround.

Thanks for reporting and for the test case!