Face materials

BlockoutSurfaces is doc 24's Surfaces table run against a scene: assign a material to a face selection, project its texture coordinates, transform them, and set its smoothing. MaterialCommand is one assignment on the undo stack; SceneFaceMaterialData is what a .vxscene carries for it.

The arithmetic is MeshSurfaces'. What is here is the half that needs a scene: which asset, which entity, and which entry in the history.

Making a block-out read as a space rather than as a grey mass. Brick on the walls, metal on the gantry, and a checker on everything nobody has dressed yet.

You do not want it for an authored mesh's material slots. Those are the model compiler's, and a MeshRenderable names one material for the whole mesh.

A material is assigned to a face's group, not to the face. That is what face groups are for: a wall's twelve faces after two bevels are still one wall, and an assignment remembered per face index is one that the next loop cut renumbers out from under.

⚠ Assigning a material does not demote a parametric shape and everything else here does. The assignment lives on the document beside the mesh, so regenerating the geometry from its parameters leaves it exactly where it was — which lets a designer dress a corridor and still make it a metre wider. A projection writes into the mesh's own corner layer, so a shape that stayed parametric would lose it the next time anybody nudged a number.

⚠ An empty selection means the whole object here and means nothing in BlockoutGeometry. "Project the UVs" has a sensible whole-object reading and "extrude" does not.

⚠ Regroup is the explicit step between "these faces" and "this material". A generator's groups are the ones a designer wants nine times in ten — a staircase's treads, a doorway's reveal — and splitting silently on assignment would make every material assignment a change to the mesh's structure.

Two materials on one mesh are two draws, and the viewport does the splitting itself:

⚠ One piece per group only when a group actually names a material. A block-out is nearly all one material, and splitting every wall into six pieces because a box has six groups would be six uploads and six draws for one picture.

The checker is what an unmaterialled surface draws with, and its squares are the work plane's step:

⚠ World space, computed in the shader from the fragment's position. A block-out box scaled 8×3 must not stretch its texels, and what makes proportion readable at a glance is a square that is the same number of metres everywhere — so the checker is a function of the world position and the world normal, and nothing about the object reaches it. That also means it needs no UV layout and no texture: two lanes on the instance the shader's own README had been calling reserved.

⚠ Filtered by the screen-space derivative, which is what "legible at grazing angles" costs. A checker sampled per pixel with no filtering becomes a shimmering moiré the moment a cell is smaller than a pixel, which on a floor is most of the floor. Fading the contrast out as the cell shrinks below a couple of pixels is what a mip chain does for a texture, in four instructions.

⚠ The axis tint is small on purpose. It is there so that a wall and a floor read as different planes at a glance; a strong one makes every screenshot look like a debug view, which is what makes people turn the whole thing off.

• Mesh surfaces — the projections and the smoothing rule.
• The shape tool — what generates the groups these are assigned to.
• Element selection — how a face selection is made in the first place.
• Editable meshes — where a face's group and smoothing group live.