Mesh surfaces

What it is#

MeshSurfaces is the half of a mesh that is not its shape: the texture coordinates on its corners and the smoothing groups on its faces. UvProjection is which of three ways coordinates are worked out — world, box or planar.

It is pure arithmetic over the mesh's own arrays. Nothing here knows what a material is; that is the editor's, in face materials.

What it is for#

Making a block-out readable. Grey on grey is a shape you cannot judge the size of, and a checker whose squares are a fixed number of metres everywhere is what turns "how wide is that corridor" into something you count. Smoothing groups are the other half: they are what stops a generated cylinder coming out as a polygon.

You do not want it for unwrapping. Every unwrapper answers "where on this surface am I" and needs the surface to have been laid out; a block-out has not been laid out and never will be, because it exists to be replaced.

World is the default and that is the decision. A block-out box scaled 8×3 must not stretch its texels, and the only projection whose squares are the same size on two objects of different scales is the one that ignores the object entirely.

Using it#

MeshSurfaces.Project(mesh, faces: null, UvProjection.World, scale: 1f, toWorld: transform);MeshSurfaces.AutoSmooth(mesh);

⚠ **Coordinates are per *corner*, not per position. A cube's corner is three corners in three faces with three different coordinates, which is exactly why the drawing structure and the position graph are different graphs — a projection that wrote per position could not map two faces of one box differently, which is the whole point of a box projection.

⚠ A face that is not named keeps the coordinates it had. Mapping a wall and finding the floor remapped is what makes a per-face tool useless.

⚠ A hard edge is the absence of a smoothing group, so zero is a value rather than a sentinel.** AutoSmooth numbers its groups from one and leaves a face with no neighbours inside the angle at zero, because "smoothed with nobody" and "hard" are the same picture and the first would fill a saved mesh with a group per face.

Examples#

Smoothing is a union-find over faces across shared edges, not a flag per edge:

MeshSurfaces.AutoSmooth(mesh, angle: MeshSurfaces.DefaultSmoothingAngle);var normals = MeshSurfaces.Normals(mesh);   // one per corner, honouring the groups

⚠ It has to be transitive. Every neighbour round a cylinder is within the angle, so the whole wall is one surface — and a flag per edge would make a corner between two smooth faces depend on which of them the normal was computed from first.

⚠ Averaging is weighted by area rather than counted. A cap's fan puts a great many tiny triangles at the pole and one big quad beside it; an unweighted average there is a normal dominated by the tessellation rather than by the shape, which is the classic pinched highlight at the top of a sphere.

A per-face transform turns about the face's own centre:

MeshSurfaces.Transform(mesh, [face], offset: new(0.25f, 0f), rotation: MathF.PI * 0.5f);MeshSurfaces.Fit(mesh, [face]);

⚠ About its own centre rather than about the origin of the mapping. Rotating a face's texture a quarter turn about a point somewhere off in UV space moves it out of the frame as well as turning it, which is what makes a rotate field feel broken — and is what a naive matrix multiply does.

See also#

• Editable meshes — where the corner layers and the face groups live.
• Block-out shapes — what generates the faces these map.
• Face materials — the editor verbs, and what a viewport does with them.
• Mesh operations — the verbs that carry smoothing through an edit.