Texture Stitching

[temportalflux]

• Textures can be stitched into a small number of atlases whose dimensions are a power of 2 (i.e. 1024x1024)
• Atlases can be uploaded once and the CPU knows which atlas sampler to associate with which draw call.
• Models rendered with stitched textures need to have uniform scale and offset variables to convert a given texture UV set ([0, 1]) to atlas space (scale(uv) + offset). This can be 1 vec4 where xy is scale and zw is offset
• Uniforms are determined based on the number of texture slots in a model asset & what textures are provided by a block asset
• Stitching the textures for a project means:
• • keeping track of all the assets for a given type (already done via AssetManager)
• • gathering pairs of texture references based on the sampler assets
• • copying pixel data from each texture into an atlas, and storing the <scale, offset> in a registry with a varying key (could be based on block asset id for example)
• Rendering a given asset means looking up the stitched data in the registry, sending the texture binding for the atlas, and sending uniform data for the provided faces in uniform binding slots. Shaders can interpret slots somehow else (probably via uniforms for cubes)

[temportalflux]

Needs to be broken up into subtasks

[temportalflux]

Misc Notes

Could provide a mat4 which contains 12 floats (6 vec2) for UV offsets per face, but how would the shader know which offsets to apply? If a normalized orthogonal vec3 was also sent per vertex, we could use it to lookup the offsets algo: Normal.x != 0 => row 1 Normal.y != 0 => row 2 Normal.z != 0 => row 3 sign(axis value) => column structure: -X U, -X V, +X U, +X V -Y U, -Y V, +Y U, +Y V -Z U, -Z V, +Z U, +Z V 0 , 0 , 0 , 0 Better yet, since mat4 takes up for slots anyway, just send 3 vec4s where each vec4 is a axis face set. If tex coords per vertex could be locked to [0, 1], we could instead pass a scalar multiplier as a uniform per draw call which would indicate how to scale down the tex coords to represent their true size in the stitched atlas. Paired with the offsets should be able to take [0, 1] -> scale([0, 1]) + offset -> [u, v]

[temportalflux]

See https://github.com/temportalflux/TemportalEngine/issues/18 for more ideas

[temportalflux]

Texture Stitching and the editor UI both will require:

• Registry of all texture assets so the engine knows what atlas sampler to associate with what block type/draw call
• Samplers can be created in editor and referenced in other assets

Assets used in texture stitching should never exceed or match the size of the atlas. In truth, they should never be more than a fraction the side of the atlas. It would be best to define these parameters on a per-stitcher basis.