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Hi,
I'm a bit surprised that I have not gotten a response to this. What I'm
seeing looks very much like a bug in Leopard OpenGL, one that makes the
fast path for texture downloads unusable for GL_ALPHA.
Regards,
Uli
Ulrich von Zadow wrote:
> Hi,
>
> using glSubImage2D with internal format GL_ALPHA,
> GL_TEXTURE_RECTANGLE_EXT and Pixel Buffer Objects exposes some strange
> behaviour (NVidia 8600 driver). Here's a partial opengl profiler log
> (I'd attach the complete one but it's too big for the list):
>
> glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
> glGenTextures(1, 0x18616a48);
> glActiveTexture(GL_TEXTURE0);
> glBindTexture(GL_TEXTURE_RECTANGLE_EXT, 1);
> glTexImage2D(GL_TEXTURE_RECTANGLE_EXT, 0, GL_ALPHA, 48, 48, 0, GL_ALPHA,
> GL_UNSIGNED_BYTE, 0x00000000);
> glBindBuffer(0x000088ec, 1);
> glBindTexture(GL_TEXTURE_RECTANGLE_EXT, 1);
> glTexSubImage2D(GL_TEXTURE_RECTANGLE_EXT, 0, 0, 0, 48, 48, GL_ALPHA,
> GL_UNSIGNED_BYTE, 0x00000000);
>
> The top line of the texture is downloaded correctly. All other lines are
> copies of that line.
>
> Some more data points:
> - The same code works correctly on Tiger (both PPC and Intel), with
> NVidia Linux drivers and with NVidia Windows drivers.
> - Changing the last parameter of glTexSubImage2D (the offset into the
> PBO) to something other than a multiple of - I think - 128 causes the
> bug to disappear.
>
> I've implemented a workaround using GL_RGBA instead of GL_ALPHA, but
> that's likely to be an extreme speed hit - these textures are y, u and v
> planes of video frames. Any other ideas for workarounds? I could use an
> offset into the PBO, but I assume that that causes the driver to leave
> an optimized (abeit buggy) path? Is there anything I might be doing wrong?
- --
Ulrich von Zadow | +49-172-7872715
Jabber: email@hidden
Skype: uzadow
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