DrftMaterial

A bought asset frequently carries no material data worth the name and yet names its materials perfectly well: the one this format was built against stores every surface as the same default grey with no transparency, while calling them body, glass, chrome, tire_mat5 and calipers. The name is then the only thing in the file that says what a surface is, so it is carried rather than discarded, and a scene can dress an import without editing the import.

Written by any baker that can derive it, and bound by nothing yet. Normal maps ship in the renderer; carrying one through the container is the plan after ORM's. The field is defined here rather than appended later so that all four indices cost the format one minor version instead of three — see MATERIAL_INDICES.

A factor that multiplies a texture is not a value, which is the mistake this pair exists to stop repeating. roughness and specular above are the scalars a material states when it has no map; these are what the same numbers mean when it has one.

glTF assigns G and B of a metallicRoughnessTexture and says nothing about R, so occlusion is only there when occlusionTexture names the same image — which is what the ORM convention is. Anywhere else this is 0, because reading R would be reading whatever the exporter left.

Distinct from specular, which is the strength of a highlight from a light. A surface can take a sharp highlight and reflect nothing, which is most plastic, or reflect its surroundings strongly, which is what makes paint and chrome read as what they are.

A test, not an opacity, and the difference is the whole reason this field exists. A cutout says which texels of a surface are there at all — the gaps in a grille, the space between leaves, the holes in a fence — and leaves everything it keeps at full strength. An opacity says how much of the light passes through the surface that is there. A format with only the second has to spend it on the first, and SurfaceMaterial.cutout had no way through the container until this: an alpha-tested surface arrived as a solid rectangle or as nothing.

glTF states it exactly — alphaMode: 'MASK' with alphaCutoff, which defaults to 0.5 — and it is what a vehicle format's alpha-test reference is, on the materials that say they are tested.

A flag, because opacity could not say it. glTF's BLEND makes alpha the factor times the texture, and a factor of 1 left opacity at 1: every loader drew the material opaque and a leaf's shape, which is all in its texture's alpha, was never read. Absent means false, which is what every file before 1.18 meant.

glTF's doubleSided, and what a curtain, a flag and a leaf card are. A one-sided surface is culled from behind, so a curtain seen from the other side of its arch is a hole, and half a tree's cards are not drawn. Absent means false, which is how every surface before it was drawn.