Hi Jason,

Does your texture come with a full mipmap chain? If that's the case it would be better to see what happens without mipmaps and just point filtering.

On which platform are you working? 

Some drivers with low quality settings may set by default a positive LOD bias. Are you (inadvertently?) modifying the textures LOD bias at all?

Marco

On Sat, Aug 7, 2010 at 2:20 PM, 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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