Direct3D texel offset perchance?

http://msdn.microsoft.com/en-us/library/bb219690(VS.85).aspx

On 7 August 2010 22:20, Jason Hughes <jhughes@steelpennygames.com> wrote:
I've been trying to resolve an issue where full screen textures being
drawn through the 3D system appear blurry.  I feel like I'm probably not
considering something.  Any ideas would be welcome!

- I'm using an orthographic projection matrix along Z, a view matrix
that is pretty much identity except for some negations on various axes
to correct for LH/RH differences in the engine.
- The quad is mapped to the full screen both for vertex positions and
UVs (0,0,1) to (1,1,1), since the ortho matrix is 0..1, not in screen
pixels.
- The texture has the exactly the same number of pixels in both
directions as the back buffer.
- Back buffer and window match resolution exactly.
- Resolution is 1024x600 (but problem exists in other resolutions)
- Texture sampling is bilinear or anisotropic (shouldn't matter).  Both
show the problem.  Sometimes my 2D stuff needs to cleanly scale, so I
can't force point sampling globally.  Texture matrix is disabled.

Steps I've taken to debug:
- I made a simple texture with regions that are alternating white and
black columns and rows that are 1, 2, and 4 pixels wide, so I could see
what was happening with texture sampling.  The result is an even gray in
the 1-pixel wide areas, but can be made brighter and darker depending on
the offset I put into the matrices.  Half-pixel adjustment didn't fix
it.  I never get white or black lines.
- I checked to make sure that the test image wasn't being munged by the
texture processing tools and it's perfectly clean (no GIGO).

I can understand not getting perfect rasterization vertically due to the
height being a non-power-of-two, but I expected columns to be cleanly
mapped.  What else should I be looking for?

Most appreciated,
JH

Jason Hughes
President
Steel Penny Games
Austin, TX


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