Sculpt and paint mode

TerrainMode is the third viewport mode, after Select and Blockout. It claims the terrain command context, puts eight tools on 1–8 and the brush controls on [, ], - and =, and hands every pointer gesture in the pane to TerrainEdit — which owns the terrain, the layer being written and the drag in flight.

The panel is three [DataContract] settings objects with [Inspector] members: TerrainCreateSettings (create and manage, with its derived readout), TerrainBrushSettings (the brush section) and TerrainToolSettings (the parameters under it). This assembly draws nothing.

Building a level's ground without leaving the viewport, and getting every stroke back with one undo. You want it whenever the terrain is being authored; a terrain being merely displayed needs none of it.

That is the whole of the registration. The mode bar, the palette entries, the radio state and the keymap follow from it — see editor modes.

⚠ The digits are doc 24's B2 a second time, and that is the point. 1–8 are view-bookmark recall everywhere else; these commands declare a context and the bookmarks declare none, so KeyMap files the two separately. A second consumer of the mode seam cost a Context string and nothing else, which is what a seam with one implementation could only assert.

⚠ A mode with no terrain shows the create panel rather than an empty toolbar. The tool commands are registered and disabled rather than hidden; entering a mode that does nothing and says nothing is the state every one of these toolsets puts a new user in.

TerrainFacts is what the form costs, computed as it is filled in: the extent, the sample count, the height and weightmap storage, the number of collision shapes, and the vertical precision. Every row is labelled (derived).

⚠ This is the dialog where a person accidentally asks for eight gigabytes. Four numbers that each look reasonable multiply into a terrain nothing can load, and the multiplication is not one anybody does in their head.

⚠ The tile size is offered in quads and stored in samples. An artist reads 63 / 127 / 255; Jolt requires a power-of-two sample count and refuses anything else by returning nothing at all. The two differ by one and the form is where the translation happens, once.

⚠ Consequence says what applying the form to an existing terrain would cost, before rather than after: cropping discards what is outside, and a height-range change rescales every height to keep its metres and spends the precision.

⚠ Merging is off. Two strokes are two undos, which is what an artist means by "undo that" and what every paint application does. What merges is inside the stroke: a drag is one record being extended rather than four hundred commands.

⚠ The brush is snapshotted at Begin and never read again. The panel can move while a drag is in flight — a pen's barrel wheel, a key, another window — and a stroke whose radius changed halfway has an undo record sized to a footprint that no longer matches what it wrote.

⚠ The composite is resolved per stamp; the colliders are rebuilt once. The first is what makes the ground move under the brush instead of jumping at pointer-up. The second is because a stroke marks the same one or two tiles over and over, and building a Jolt height field per stamp is the version that stutters.

⚠ The command is a redo the first time it runs. It is built at pointer-up from a stroke that has already been applied, so CommandStack.Execute reapplies exactly what is already there — the price of one vocabulary for undo, and the same shape every other editor command has.

⚠ Holes get their own stroke type, because a hole is not a delta. The seven sculpt tools write signed offsets into an edit layer; a hole is one bit on the terrain, with no alpha and no stack. TerrainHoleStroke is the parallel record, and recording a bit in a delta record would restore the wrong container's contents.

⚠ The ramp previews by undoing itself. A ramp is one shape between two points rather than stamps that accumulate, so each move of the second point undoes the stroke and redraws it — which works only because the record captures its before-image lazily.

TerrainCategory is Sculpt or Paint. Both need a terrain and both act on its texels, so they are one mode; what differs is whether a stamp writes a height or a weight. Unreal spells the same split as tabs within Landscape mode.

⚠ The digits are bound to slots, not to named tools. Binding "Sculpt" and "Paint Layer" both to 1 in the terrain context puts two commands on one chord, and the keymap resolves that to whichever registered last — silently, and differently depending on registration order. terrain.tool-N means what the design sentence means, "the third tool", and the named commands keep the words an artist searches the palette for.

⚠ A digit past the current category's tool count does nothing rather than wrapping. Wrapping round to the first tool is the version that silently paints with the wrong one.

⚠ Changing category mid-drag abandons the stroke, for the same reason changing tool does: a stroke is a record of what one tool did, and finishing it under the other category would commit an entry whose name and whose record belong to two different operations.

⚠ A paint stroke rebuilds no colliders. No height moved, so the shape is the shape it was; what changed is which material each quad is, and that is read from the weights when it is asked. The first version rebuilt anyway and a test caught it.

TerrainLayerSettings is the .vxlayer form and TerrainTargetRow is a row of the list above the strip. Selecting a row makes it the paint target.

⚠ The layer being painted changes far more often than the tool, so the list is above the strip and not in it. That is Unreal's layout and it is correct: an artist paints grass, then rock, then grass again with the same tool, and making the layer a mode would make that three mode switches.

⚠ The coverage is one number, not a histogram. A per-layer histogram over four million samples is a bar nobody reads; what the section is for is "this layer is at zero and I do not know why" — the state you get into by painting over your base layer — and a percentage answers it.

⚠ Removing a target layer records every channel, not just the one removed. Its weight goes to the others in proportion, which is not invertible from the layer alone: putting the channel back would leave the rest holding what they were given.

TerrainLayerCommands is the panel's verbs, each one entry: add, remove, duplicate, move, clear, collapse, rename, show/hide, lock, and the two alphas.

⚠ A removed layer is held by its command, not rebuilt from a name. An undo built on AddLayer puts back a layer with the right name and none of its deltas — which passes any test that counts layers and loses an hour of sculpting. Terrain.InsertLayer exists for this and nothing else.

⚠ The alphas merge and the toggles do not. A slider drag is three hundred changes and one edit; a visibility toggle is one of each. The merged command undoes to the value before the drag started, which is the half of TryMergeWith's contract that is easy to get backwards.

⚠ A clear swaps contents rather than replacing the object. The panel's selection, the mode and a stroke in flight all hold the layer by reference.

ITerrainColliders is an interface for the reason IMeshBaker is one: nothing in the editor references Vixen.Physics, and this does not either. The editor says which tiles moved; whatever holds a physics world turns that into shapes.

⚠ Through TerrainDescription.TilesOf, which answers with both tiles for a sample on a boundary. A stroke along a tile edge that rebuilt only one side leaves a strip of collision disagreeing with the ground beside it — a lip the player trips on, on a seam nothing draws.

⚠ Null is a terrain with no collision, not an error. A scene being sculpted before anybody has pressed play has no physics world, and a mode that refused to work without one could not be used until the game ran.

The implementation is TerrainColliders, in its own assembly, and TerrainModule assigns it from PluginServices when the host published one.

A stroke driven from world points, which is what a test does and what the pane does with a ray:

A refusal, which is a sentence rather than an exception:

⚠ A brush that silently does nothing is the version of this that gets reported as the tool being broken. Locked layers and generated layers are ordinary things to aim at.

The create form's readout, which is what stops a terrain nothing can load:

• Editor modes — the seam this is the third consumer of.
• Foliage mode — the fourth, and why foliage is not a category of this one.
• Sculpting a heightfield — the kernels behind the sculpt tools.
• Painting a terrain — the kernels behind the paint tools.
• Terrain brushes — what TerrainBrushSettings produces.
• docs/plan/31 § T3 — the phase this is, and its exit criterion.