Line rendering vertex coloring

[Korijn]

See comment #69 (comment) for pictures

• Adds vertex coloring support on all line materials.
• Updates axes helper to leverage vertex coloring (is now a single world object instead of four).

I also wanted to make sure we have a good testcase for pygfx/pyshader#55 as you can tell by the duplication in the shaders

[almarklein]

Fixed in a commit. I can see that this is easy to overlook. Would be good to hard-set uinform types like this in the renderfunction ...

[Korijn]

I totally overlooked that :) thanks.

How would you suggest I clean this PR up (avoid all the copy paste)?

[almarklein]

mmm, pyshader does not have functionality for calling into functions yet. It looks like we need it more and more. For now I'd leave it as-is.

One thing that was not yet clear to me is whether we'd need a separate material for this. We could, for instance, let the per-vertex color override the material's color if it is present on the geometry. How does ThreeJS doe this?

[Korijn]

As far as I know, materials in threejs have "optional" uniforms. When you add or remove (not update!) one, you set "needsUpdate=true" on the material and in the next render call the shader is reconstructed (with templating) and recompiled.

There's also material "parameters" which do not map directly to uniforms such as "vertexColors=true/false" but also need "needsUpdate=true" to trigger the same shader reconstruction and recompilation process.

Play around with this: https://threejs.org/docs/index.html#api/en/materials/MeshBasicMaterial

And look at the source to see how that demo scene is implemented: https://github.com/mrdoob/three.js/blob/dev/docs/scenes/material-browser.html

So no, you don't need to use separate materials for this.

[almarklein]

Ah, its a boolean on the base Material class: https://threejs.org/docs/index.html#api/en/materials/Material.vertexColors

[Korijn]

Ah, its a boolean on the base Material class: https://threejs.org/docs/index.html#api/en/materials/Material.vertexColors

I guess if we would want to support the same feature, we would need to have a vertexColors prop on material that is somehow also a Resource object, so as to hook into the update mechanism, right?

Perhaps I can simply call self._bumprev in a setter as well.

[almarklein]

The vertexColors prop can be a bool. If you implement the setter to call _bump_rev, then any parent WorldObject's will be bumped as well, and thus trigger a pipeline rebuild.

[Korijn]

Did that; don't support it on thin lines yet.

[Korijn]

Axes helper is now a single world object with line segment material vertex coloring:

Added support for thin lines as well:

[almarklein]

LGTM!