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PT_Barn
08-26-2006, 01:55 PM
I'm using OpenGL 2.0+ (ATI X600 card) on linux.

I was getting texture corruption (and system hangs) when playing a video to a texture. The video player system decompresses to a chunk of memory. I then upload the new video frame to a texture using the standard calls (done outside the Rendering loop):

glEnable( GL_TEXTURE_RECTANGLE_EXT );
glBindTexture( GL_TEXTURE_RECTANGLE_EXT, textureID );
etc. etc.
glTexImage2D( GL_TEXTURE_RECTANGLE_EXT, ....., imagePtr );
glDisable( GL_TEXTURE_RECTANGLE_EXT );

inside the rendering loop, I draw the texture as a Quad.

Depending on system load, I get corruption in the video image sometimes and/or linux hangs. I added a bunch of cerr's before and after the video codec calls, this mysteriously fixed the problem which lead me to believe it was a synchronization problem. So in the above code, I added a 'glFinish()' call before I upload the video frames pixels to the texture. This fixed the problem. My thinking is that the draw code's opengl calls were being queued up and the texture would sometime get changed while it is being drawn. Is this correct? I can understand the image corruption, but why would it hang? Wouldn't this upload code still be legal?

Would a double buffer texture upload scheme fix the problem without having to 'glFinish()'?

thanks for any help.

John

xavirn
08-26-2006, 11:38 PM
try to use the function ''glTexSubImage2D'' to update the texture

PT_Barn
08-27-2006, 07:17 AM
Originally posted by xavirn:
try to use the function ''glTexSubImage2D'' to update the texture Why? Is this faster or synch's up better? I'll look over the function spec in the meantime. Thanks.

Zengar
08-27-2006, 07:59 AM
TexSubImage2D is faster, as TexImage2D actually defines a new texture. You can also look into ARB_pixel_buffer_object (is it supported by ATI?)

PT_Barn
08-27-2006, 08:44 AM
Originally posted by Zengar:
TexSubImage2D is faster, as TexImage2D actually defines a new texture. You can also look into ARB_pixel_buffer_object (is it supported by ATI?) Thanks! I re-read the TexSubImage2D spec and it makes sense. But, out of curiosity, say I had a Gl_Quad setup to render with a texture, but then modify the texture while it is being rendered? Is this possible? Would it cause problems?

Mikkel Gjoel
09-02-2006, 04:42 PM
It is not possible... probably because it would cause problems :) You can update the texture between frame-renders though.

Korval
09-02-2006, 06:58 PM
But, out of curiosity, say I had a Gl_Quad setup to render with a texture, but then modify the texture while it is being rendered? Is this possible? Would it cause problems?No. Not unless the driver is buggy. The spec specifically states that the driver is to deal with such circumstances.

In this case, the driver will almost certainly execute a glFinish inside your glTexSubImage call, thus stalling your CPU until it can schedule the upload.

If you're using a PBO, it may not have to flush, as it might be able to push a DMA command into the command pipeline itself.