Optimize corner quad generation

[limbonaut]

• Distortions appear because we rely on normals in the process of building the quad.
• Reworks algorithm to rely on delta vectors instead.
• Aligns better with overall shape geometry, and also improves results of render_offset.

[limbonaut]

I can rebase it after #156 is merged.

[mphe]

Code looks fine, but I'm also not that familiar with the inner edge generation workings.

What exactly does this PR fix? Is it related to #156? Would it affect the outcome of #156, i.e. does #156 need to be tested with this PR or the other way round?

Can you provide an example image how it improves distortions?

[limbonaut]

#156 introduces a set of changes, one of which, as you know, is corner anti-distortion code. This PR achieves the same result, but instead of compensating for the "bad" generation result, it instead generates a "good" one. So the code is simpler and faster. As a side effect, this approach also improves render_offset results - additional benefits. This PR would be in direct conflict with #156, that is why I offered to rebase it after we merge that one. I my tests, unless you use render_offset, the result would be identical to #156 (when it comes to corner distortions ofc - that PR is much more than dealing with distortions).

[mphe]

Ah, thanks for clarifying.

[limbonaut]

Ready for review.
Test scene: corner_anti_distortion.zip
Rebased on current master.

[mphe]

Besides the small optimization, LGTM.

[limbonaut]

Besides the small optimization, LGTM.

Thanks, fixed it and merging 👍