Add gram-schmidt fast approximation tangent generation algorithm

[aloucks]

Provide a fast alternative algorithm for tangent generation

Fixes: #17834
Related (maybe): #17877

Solution

Add a new enum TangentStrategy that gives the user the option to select how tangents are generated.

The GLTF loader now has a property to set which algorithm is used for models that are missing tangents.

The FastApproximation strategy is implemented with the Gram-Schmidt fast approximation technique. The HighQuality variant uses MikkTSpace.

Testing

Unit tests have been added to assert that both tangent computation strategies produce similar tangents for simple shapes. I also tried to check several examples to verify that the visual results are acceptable with both algorithms. I wasn't able to tell any visible difference.

How can other people (reviewers) test your changes? Is there anything specific they need to know?

I checked the deferred_rendering, parallax_mapping, and anisotropy examples. Suspiciously, when I produced intentionally invalid tangents, the deferred_rendering and parallax_mapping examples seemed to render fine. I didn't try the anisotropy example with intentionally invalid values. I'm curious if there is an unrelated bug in the shader where tangents are ignored (or the examples I tested somehow didn't leverage tangents).

Migration Guide

• GenerateTangentsError::MikktspaceError has been renamed GenerateTangentsError::AlgorithmError
• The Mesh::generate_tangents and Mesh::with_generated_tangents methods are now deprecated. They are replaced by compute_tangents and with_computed_tangents, both of which accept a TangentStrategy parameter. The naming conventino of these methods now matches compute_normals.

[JMS55]

Suggested change

	pub computed_tangent_strategy: TangentStrategy,
	pub tangent_calculation_strategy: TangentCalculationStrategy,

[aloucks]

renamed

[hukasu]

the anisotropy example does use tangents, this issue shows some issues caused by not optimal tangents #16179

[hukasu]

i was making tangent generation for the primitives, but with a very naive algorithm #17691, if your method works without causing seams then my PR becames redundant

[aloucks]

the anisotropy example does use tangents, this issue shows some issues caused by not optimal tangents #16179

The sphere looks much better with the gram-schmidt tangents. I actually left Sphere out of the tests that I added because there was at least one vertex where the mikktspace generated tangent differed from the gram-schmidt tangent enough that it was outside of the test threshold.

mikktspace

sphere_mikktspace.mp4

gram-schmidt

sphere_gramschmidt.mp4