Alt-applying textures from angled faces causes crooked textures on target face

[mariteaux]

If you have an angled face and you apply its texture to another angled face, for whatever reason, the texture will appear angled on the second face, despite not having an angle value. It's a bit hard to explain, so here's a visual.

I think this only happens on faces angled vertically. If you apply it to a horizontally-angled face, it'll appear fine. The easiest way to recreate it is by making the light posts from E1M1 and applying one side's texture to another side.

I'm using the Valve220 format for what it matters; in J.A.C.K., it reports the original face as being a world normal and the weird crooked face as a face normal.

[mariteaux]

Since it was suggested that I upload the map you see up there, here's an autosave.

[kduske]

@ericwa is that an easy fix?

[ericwa]

I think it's an easy fix, but I'm not sure exactly what to do.

The alt+click code (ParallelTexCoordSystem::doUpdateNormalWithProjection) is detecting that it needs to rotate the source face's texture vectors by 90 degrees in order for it to project on to the dest face.
It currently rotates about cross(source face normal, dest face normal).

1. We could try rotating 90 degrees about cross(snapToAxis(source face normal), snapToAxis(dest face normal)).
2. Another possible behaviour is rotating 90 degrees about one of the two texture vectors (try both rotations, and use the first one where both vectors project onto the dest face normal with a non-zero length).

Aside:
These light fixtures have axis-aligned texture vectors ("World alignment" in Jack/Hammer terminology) rather than being on the face plane ("Face alignment" in Jack). Solution 2 would behave differently depending on whether the texture vectors are in the face plane or not.

For reference here is a test case with the left light fixture using world alignment and the right one using face alignment:
worldalignment_facealignment.map.txt

[ericwa]

I went with solution 2, as it feels more correct and will work correctly on rotated brushwork.
I think solution 1 is a hack (also, it might be the case that a face has a valid texture projection, but snapping the face normal to the nearest axis causes the texture projection to be invalid).

However, the caveat is that the plane of the texture axes matters. Alt-click will only give the "desired" result on this light fixture if the source face is world aligned, i.e. the texture axes lie on an axial plane and not the face plane. The provided map file has world-aligned texturing since it was converted from vanilla texturing to valve 220, so alt+click gives the desired result with my PR.

I think we'll need a "reset to world/paraxial" button, and ideally some kind of visualization like JACK has. I'll open a separate issue for that.

[ericwa]

Here is a summary of the behaviour with my PR. The PR only touches alt-click.

There are 4 cases: (source face is world-aligned, source face is face-aligned) * (alt-click, shift-alt-click):