Am 26.10.2016 um 17:43 schrieb William F Pokorny:
> On 10/25/2016 12:55 PM, Le_Forgeron wrote:
>> Le 23/10/2016 à 17:05, William F Pokorny a écrit :
>> You should also have a look at box uv_mapping... it's strange too.
...
> That said, we could I think, get to where an image/pattern as viewed  on
> a plane would map more naturally onto the box as if wrapped in U like
> other patterns.
> 
> I'd say we take starting and ending mid face on the +X face out of
> consideration, but keep the idea of the map starting/ending on the +X
> face to better match our other maps. Are you then thinking of folding
> from +x backward for Y top/bottom using a map something like this?
> 
> Ymax
> Xmax Zmax Xmin Zmin
> Ymin

If we make any changes to the box uv_mapping at all, let's avoid rolling
our own again, and instead pick a format from among those "in the wild".

Potential candidates that spring to my mind are some 360 degree panorama
formats:

- Paul Debevec's "Vertical Cross Cube" format
- Quicktime VR cubic format
- SPi-V cubic format

As far as I can tell, the Quicktime VR format happens to match POV-Ray's
current box UV mapping (remember that in 360 degree panoramas you're
inside the cube), provided POV-Ray's default left-handed coordinate
system is used.

Also, the vertical cross cube format is reasonably compatible with it:
Rotating the texture by 90 degrees counter-clockwise, and compensating
by rotating the box by 90 degrees clockwise, should do the trick.


> Suppose a significant amount box-uv/warp{cubic} mapping in scenes. Add
> an alternate box mapping? What is the complexity of another box mapping
> compared to mirroring in U(x) the pattern/image prior to
> box-uv_mapping/warp {cubic}...

Introducing alternative UV mappings not only to the box primitive but to
all shapes seems to have some merit, as the same internal mechanism
could also be used to solve the problem of left-handed vs. right-handed
coordinate systems.

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