Am 21.06.2016 um 22:29 schrieb Bald Eagle:
> Is there a reference that better explains uv-mapping for bezier patches?

It seems that although the `uv_vectors` keyword did make it into
POV-Ray's `bicubic_patch` implementation it never made it into the
documentation.

Given that the feature first appeared in MegaPOV, it would be logical to
search through old MegaPOV docs for a precise description of what it does.


Contrary to what Jerome posted, the UV coordinates are not interpolated
between 3 points, but between all 4 of them.

Imagine the bicubic patch as a rubber sheet; then the UV mapping can be
visualized as follows:

- First, the rubber square is stretched across the XY plane; the corner
points are pegged to the coordinates specified in the `uv_vectors` list,
while all the points along the edges are also pegged to the plane to
keep the lines between the corners perfectly straight.

- The specified texture is "printed" onto the thusly stretched (and
possibly skewed) rubber square.

- The rubber square is relaxed again to its original shape; note that
depending on the choice of `uv_vectors` it will now show a scaled,
stretched and/or skewed version of the specified texture.

- The rubber square is pulled into the final shape as dictated by the
control points, potentially distorting the texture even further.

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