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Texture precision

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I'm working with 2D using textured quads and am having some difficulty getting images to display precisely. If I turn off texture filtering, the images are displayed perfectly, but look terrible when rotated and scaled. If I use texture filtering then the images show artifacts. For example: Notice that the one on the right has a darkened border on the top and left. It was drawn with texture filtering on, and as a result the right and bottom wrap around a bit to the left and top. Of course, the one on the left is pixel-perfect now, but if I rotated it it would look pretty bad. This quad in particular uses an entire image file, so the vertices' texture coordinates are just (0,0) to (1,1) - can't really get any more precise there. Is there anything I can do? Thanks, Max [Edited by - _Flecko on June 12, 2005 11:10:04 PM]

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A couple of things to check out:

1) Mapping texels to pixels:

Also check the topic in the DirectX SDK docs:
DirectX Graphics ->
Programming Guide ->
Getting Started ->
Direct3D Textures ->
Texture Coordinates ->
Directly Mapping Texels to Pixels

2) Try setting the D3DSAMP_ADDRESSU and D3DSAMP_ADDRESSV sampler states to D3DTADDRESS_CLAMP

There are a couple of issues to think about:

a) the position of a pixel in D3D represents its centre rather than a corner - if you don't take that into account, assuming no anti-aliasing, the rasterizer will miss out some texels in cases where a pixel at outer the edge of the polygon is ever so slightly off-centre.

b) with bilinear filtering, the average of texels around the sample is taken - consider what happens when the sample point is right at an extreme edge of the texture map and the hardware needs to get a sample to the right of that... That's what the address mode affects - if you have the address mode set to WRAP, then the sample for the filter will come from the *opposite* side of the texture map; the CLAMP address mode ensures that any samples from outside the extremities of the map are clamped to the nearest edge rather than the opposite edge.

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Awesome, wish I'd know this a long time ago. Draw calls for my graphics library are recursive and the public call passes an initial transformation to the private recursive call, so all I had to do was pass a (-0.5,-0.5,0) transformation instead of Matrix.Identity :P

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