I posted this on the Quartz-Dev list a bit ago, but after a bit of
investigation I'm getting stuck trying to figure this out, and the
area that I'm getting stuck in is OpenGL.
On May 27, 2007, at 1:34 PM, Jonathan Johnson wrote:
Sorry for the strange title -- couldn't come up with a smaller
summary that still made sense :) I have a NSOpenGLView which I
aquire its CGLContextObj/CGLPixelFormatObj to create a CIContext. I
then draw an image using drawImage:inRect:fromRect:. This all works
great, and my code to ensure pixel alignment works for this call.
However, I then attempt to draw some geometry in OpenGL, mainly
noticed with GL_LINE_STRIP. If I don't call drawImage, these lines
are crisp and pixel-aligned. However, after calling drawImage they
are no longer crisp -- they've undergone subpixel rendering.
I've tried to do a few things, but am out of ideas. I'm not an
advanced OpenGL developer, so I'm sure I'm just missing some
setting. I've tried glLoadIdentity() thinking it was an issue with
the matrix, I've tried re-setting up the view to its old state as
well. I'm also explicitly setting the line width to 1.0.
So I'm curious what else CIContext drawImage could be messing with
in my OpenGL context. Any ideas would be greatly appreciated.
I investigated this a bit more with OpenGL Profiler. I put a
breakpoint on glLineWidth which is after my drawImage call, and ran
my program twice under the profiler -- once with the drawImage call
enabled, and once with it commented out.
Using the state tab, I was able to find the only differences in state
between these two cases. Current Vertex->GL_TEXTURE0-
>GL_CURRENT_TEXTURE_COORDS is {52, 356, 0, 1} instead of {0, 0, 0,
1}, and secondly Textures->GL_TEXTURE0-
>GL_TEXTURE_BINDING_RECTANGLE_EXT is 2 instead of 0.
The things I was expecting to cause this behavior haven't changed --
the projection, transpose, and modelview matrixes. They are identical
with or without the drawImage call. So, the textures are the only
known differences I can see. What's odd though is that GL_TEXTURE_1D,
2D, etc. are all disabled, which would make me believe that these
settings wouldn't affect my line drawing.
Does anyone have any ideas on how these differences might be
affecting my line drawing, or any ideas on where else to look to see
what might be going on?
Thanks in advance,
Jon
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