Texture offset and repeat settings in Material

[brianchirls]

Right now, there are two ways to adjust the positioning of a texture on an object:

• UV coordinates in geometry
• .offset and .repeat properties on Texture

It would be useful to also have .offset and .repeat properties on Material as well, so that these values could be varied on different objects without having to allocate additional geometries or texture resources.

I'm considering an interesting use case: breaking down sky spheres/domes into smaller components. Rather than create a single, large, solid sphere, imagine a fraction of an icosahedron (subdivided) and repeated as multiple meshes to construct a sphere out of pieces. It would cost a few extra draw calls, but provide at least two benefits:

1. Significantly reduce the number of vertices computed by excluding the ones that are off camera, which is well more than half. Spheres can have hundreds of vertices, depending on the level of detail. This is not such a big deal on desktop, but I suspect it could make a big difference on mobile devices with tiled GPU architectures that would cause the vertex shader to be run many times.
2. Reduce overdraw by fixing z-sorting. If an entire sky sphere is positioned at [0, 0, 0], it will almost certainly be sorted incorrectly and drawn first every time, even though it should be drawn last. By positioning individual sphere components far away, they should be correctly sorted last.

Implementing this approach today would require duplicating either the geometry (for different UV coordinates) or the texture (for different offsets) for each piece of the sky. If we could set the offset on the material, each piece would use the same geometry, shader and sampler, only varying the uniform values between draw calls.

[brianchirls]

It occurs to me that the z-sorting benefit would require tweaking painterSortStable, which currently prioritizes material and shader id over z depth. I'll file a separate issue on that for discussion.

I suppose one could fix overdraw now by changing the renderOrder on sky domes, which is probably a good practice. But it's likely worth fixing overdraw anyway for other objects.

[brianchirls]

Upon further research, I'm not sure any of this is true. Please hold for additional research and benchmarks...

[brianchirls]

I've done some more research on this, and while I remain unconvinced that there's a performance benefit from breaking a sky sphere into pieces, I've run into a number of use cases where this would be beneficial. Sometimes there are simple, useful textures that can be re-used in different cases, like certain gradients, blurred masks, grids and things. I'd love to be able to have a single instance of each texture that I can use with different repeat and offset values for each material.

[brianchirls]

This is increasingly valuable, but since the original justification for this is distracting, I'm going to close this and re-file.