Block-out shapes

MeshShapes builds an EditMesh from a ShapeParameters — a ShapeKind and six numbers. Twelve kinds: box, plane, cylinder, cone, sphere, capsule and torus, plus the five that are tedious to build by hand and are why Unreal ships a Stairs tool — stairs, ramp, arch, pipe and door frame.

MeshShapes.Sweep is the routine three of those are made of, and it is also the poly-shape tool: a closed outline, swept along a line, capped at both ends.

Making the thing rather than modelling it. Half of a block-out pass is a wall, a floor, a flight of steps and a doorway, and every one of those is a shape somebody wants at a size rather than a mesh somebody wants to extrude into existence.

You do not want it for a prop an artist will make. A shape here exists to be replaced, which is the whole reason it is generated from numbers instead of authored.

Quads, wherever a quad is what the shape is made of. EditMeshes.From(PrimitiveKind) welds a triangle soup back into a mesh and cannot give back the four-sided faces the soup was built from — and an edge loop, an edge ring and a loop cut are all statements about four-sided faces. A cylinder made editable through the renderer's primitive has no rings to cut; one built here does.

⚠ Size is the whole extent in world units, and the geometry carries it. MeshPrimitives builds everything to fit the unit cube so that a transform's scale is the size, which is right when a thousand entities share one upload. It is wrong here: a wall built as a unit cube scaled 8 3 0.2 has a non-uniform transform, so every bevel it is given afterwards is wider on one axis than another and every texel on it is stretched.

⚠ Centred in X and Z, and sitting on the origin in Y. Everything a block-out tool makes is placed on the work plane, and a shape whose origin is its centre arrives half-buried in the floor.

⚠ Six fields for twelve shapes, and what each means is per kind. Sides is a cylinder's sides and an arch's segments; Steps is a staircase's steps and a sphere's rings; Thickness is the only one that is a length rather than a ratio, and it is the wall left above an opening. A record per kind would be tidier in the type system and would grow a case in the scene format, a drawer in the inspector and a branch in the reader every time somebody added a stair.

⚠ Out-of-range parameters are clamped rather than refused. The caller is a number field somebody is scrubbing through zero: an inspector that threw on a negative side count would throw once per frame, and one that refused the edit would make the field impossible to type a two-digit number into.

The poly-shape tool, which is Sweep with an outline a designer clicked:

⚠ The outline must be anticlockwise in the plane its two axes span. A clockwise one produces a solid whose faces all point inwards — which validates as closed, draws as a hole under back-face culling, and is the single most common way a generator goes wrong. BlockoutCreate.Poly reverses a clockwise footprint before it gets here, because which way round a designer drags a room is not something they should have to know.

Face groups are assigned by what a face is, not by which way it points. A staircase's treads are MeshShapes.GroupTop and its risers GroupFront whatever angle the flight is at, so "select every tread" is one click and a material given to the treads survives the flight being made steeper. EditMesh.Regroup is the other answer and is the right one for a mesh that arrived from somewhere else; a generator knows better than a tolerance can.

• Editable meshes — the structure everything here produces.
• Mesh operations — the verbs that change one afterwards.
• Mesh surfaces — how the faces these generate are mapped and shaded.
• The shape tool — the gesture and the live parameters, in the editor.