Face materials

What it is#

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.

What it is for#

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.

Using it#

BlockoutSurfaces.Assign(editing, brick);BlockoutSurfaces.Project(editing, UvProjection.World);BlockoutSurfaces.AutoSmooth(editing);

⚠ 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.

Examples#

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

scene.SetMaterial(entity, MeshShapes.GroupTop, brick);meshes.Build(scene);   // one batch per materialled group; one for a mesh with none

⚠ 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:

meshes.Checker = viewport.Grid.Plane.Effective(spacing);

⚠ 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.

See also#

• 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.