Add notes on calculating normals for non-uniformly scaled meshes

[KiSetsuFu-PuLiN]

This PR adds notes on manually calculating normals in the spatial shader for non-uniformly scaled meshes

[clayjohn]

This functionally does the same thing as render_mode ensure_correct_normals. I think it would be better to recommend ensure_correct_normals

[KiSetsuFu-PuLiN]

This functionally does the same thing as render_mode ensure_correct_normals. I think it would be better to recommend ensure_correct_normals

I tried it, but I didn't get the rendering results expected.
Actually I don't quite understand how to use the render mode ensure_correct_normals. Maybe I'm using it incorrectly?

[clayjohn]

This functionally does the same thing as render_mode ensure_correct_normals. I think it would be better to recommend ensure_correct_normals

I tried it, but I didn't get the rendering results expected. Actually I don't quite understand how to use the render mode ensure_correct_normals. Maybe I'm using it incorrectly?

Yes, you are using it incorrectly. You need to use MODELVIEW_NORMAL_MATRIX for normals.

That being said, as I looked into the details I noticed that I was wrong in my response above. ensure_correct_normals doesn't do anything anymore. We detect when a mesh is scaled non-uniformly and automatically fix the normal matrix like so:

if (bool(model_flags & uint(FLAGS_NON_UNIFORM_SCALE))) {
	model_normal_matrix = transpose(inverse(mat3(model_matrix)));
} else {
	model_normal_matrix = mat3(model_matrix);
}

So the docs should just use MODELVIEW_NORMAL_MATRIX!