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Texture coordinate geenration for sphere map #84

Merged
merged 4 commits into from
Nov 25, 2024
Merged

Texture coordinate geenration for sphere map #84

merged 4 commits into from
Nov 25, 2024

Commits on Nov 24, 2024

  1. texture: primitive implementation of GL_SPHERE_MAP and GL_REFLECTION_MAP 

    This implementation comes with a big simplification: while the OpenGL
specifications say that the texture coordinates should be computed as a
reflection from the point of view of the camera, we do it as if the
camera rays were all parallel to each other (that is, as if the camera
was located infinitely far away). This approximation is acceptable for
objects like spheres or with other curved surfaces, it works pretty
badly with flat surfaces where all the normals have the same value,
because in that case the same texel from the reflection texture gets
applied over to the whole object.

Also, GL_SPHERE_MAP should not be the same as GL_REFLECTION_MAP, because
the resulting reflection vector should also be scaled down according to
the distance from the viewer.
    @mardy
    mardy committed Nov 24, 2024
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  2. texture: implement GL_SPHERE_MAP in software 

    This implementation complies with the OpenGL specification. In a
follow-up commit we will give the client the possibility to choose
between this software implementation and the faster (but wrong) GPU
implementation.
    @mardy
    mardy committed Nov 24, 2024
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  3. Add environment variable to select accuracy vs speed 

    We might have more cases in the future, where we can choose between an
accurate software implemenation and a faster but non-standard GPU
implementation. Let's create a mechanism through which the client can
select the features which can be sped up at the cost of correct
rendering.

This is currently exposed as an environment variable, and not as an API,
because if it turns out to be a bad idea we can remove it without
breaking the public API.
    @mardy
    mardy committed Nov 24, 2024
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  4. arrays: make texture coordinate generation work with vertex buffers 

    Implement the read_{pos,norm}() functions for the DirectVboReader class
too, because they are needed when generating texture coordinates.
    @mardy
    mardy committed Nov 24, 2024
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