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scott <sco### [at] scott com> wrote:
> More specifically, when trying to map a rectangular section of a texture
> onto a non-rectangular quad in model-space. In practise this rarely happens
> because you usually match your texture coordinates to the mesh (so that the
> texture does not get distorted) - ie your 2 and 3 in texture space would be
> moved to match how they look in model space.
That's not always possible. Simple example: A torus composed of quads,
and a rectangular texture image wrapped onto its surface. The texture will
be distorted at the places where the quads are non-rectangular.
I suppose you could tansform the texture image so that it matches the
shape of the quads at each point. It would make the texture irregular and
larger, but I suppose it might work. OTOH, if you ever decide to change
the resolution of your torus (ie. change the number of quads it's composed
of), you'll have to re-calculate the texture as well, which might not be
practical.
> In screen-space, when quads pretty much always become distorted and
> non-rectangular due to perspective, the GPU accounts for this by
> interpolating the texture coordinates divided by w (the homogenous
> coordinate) to ensure the problem you illustrated in the other reply is
> avoided.
Perspective has nothing to do with what I'm talking about.
--
- Warp
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