Painting

A Rust map carries four painted layers besides its height, and Creator paints all four with the same brush: the ground textures, the biome, the topology bits and the alpha holes. The rail gives each layer its own button and its own color, and the inspector header says which one you are in, for example PAINT · Splat.

The four layers

Layer	Key	What it is	What it changes in game
Splat	Y	The ground textures, eight of them, blended	What the ground looks like and sounds like underfoot
Biome	B	Which of five biomes a place belongs to	Vegetation, ambience, and the biome-gated spawns
Topology	T	A bitmask, one bit per named kind of ground	What the game and generators treat that ground as: beach, forest, road, monument, cliff and the rest
Alpha	A	Whether the terrain surface is drawn at all	Holes: caves, tunnel mouths, anything you can see through the ground into

Every layer uses the brush you set up on Sculpting, including the shape, the falloff, the rotation, the spacing and the gates. Two differences: paint has an Opacity as well as a Strength, and the two binary layers (Topology and Alpha) have nothing to blend, so they take the brush’s footprint but not its softness.

The digits 0 to 7 pick the channel while a paint tool is active, and Esc cancels a stroke in flight without recording anything.

Splat, the eight ground textures

The eight channels are, in order: Dirt, Snow, Sand, Rock, Grass, Forest, Stones and Gravel. The inspector shows them as a color swatch grid rather than a numbered slider, so you pick the ground you want by eye, and the pill in the view names your choice as you work.

Paint Mode is the other half of the splat tool.

Mode	What a drag does
Paint	Adds the chosen channel where you drag
Erase	Takes the chosen channel out, giving the ground back to whatever else is there
Smudge (smear existing)	Smears the textures already on the ground in the direction of your drag. It shows up near a color boundary, not on uniform ground

The eight channels always add up to one at every point, so painting one channel in always takes the others out proportionally. That is the format’s own rule, not a choice Creator makes.

Biome

Five biomes: Arid, Temperate, Tundra, Arctic and Jungle. Pick one from the Biome dropdown and paint. A biome is one value per place rather than a blend, so painting Arctic over Temperate replaces it.

Biome does a lot of quiet work in Rust: it decides which trees and plants belong, and the game uses it for ambience and for some spawns. Paint it to match the ground you have sculpted, or a snowfield keeps growing palm trees.

With the map set to Semi-Tropical, the list gains a sixth biome, Tropical, which paints the Deep Sea’s tropical ground where you put it. It is off by default; see Tropical biome for what it does and what each server shows.

Topology

Topology is the map’s own description of its ground, as a bitmask: a place can be Beach and Oceanside and Mainland at once. The Topology dropdown names the first eight bits, which are the ones the digit keys reach:

Field, Cliff, Summit, Beachside, Beach, Forest, Forestside, Ocean.

There are thirty-one named bits in total, and the rest (Decor, Monument, Road, Roadside, Swamp, River, Riverside, Lake, Lakeside, Offshore, Rail, Railside, Building, Cliffside, Mountain, Clutter, Alt, Tier0, Tier1, Tier2, Mainland, Hilltop) are reachable through Multilayer topology under Advanced Paint: open that section, turn on Enable multilayer mask, open Topology bits (mask) and tick the bits you want, and one stroke writes all of them.

Set bit (off = clear) is the toggle that decides whether your stroke sets the bit or clears it, and the tool pill says which: Topology: Road or Topology: Road (clear).

Topology is what makes a hand-built area behave like the real thing. A road you draw looks like a road as soon as you paint the texture, but it is not one to the game until the Road bit is set under it. TOOLS > Clean topology under roads, rivers and monuments is the one-click cleanup for the opposite problem, the leftover Field and Forest bits under features that should have replaced them.

Layer operations

Under Layer Operations in the same panel are three whole-map edits of one bit, each a single undo step. Pick the bit in Topology layer (all thirty-one are offered here, starting on the brush’s own bit), then:

Button	What it does to every cell of the map
Clear Layer	Takes the bit off
Invert Layer	Flips it: set cells lose it, clear cells gain it
Replace Layer	Moves it to the bit picked in Replace with: a cell carrying the first bit loses it and gains the second (a cell that already had the second keeps it)

The toast names what changed and how many cells. An operation that would change nothing records nothing, so it never marks the map as edited. These touch only the topology: the biome, the Tropical layer and every other layer are left exactly as they were.

Alpha, the holes

Alpha decides whether the terrain surface exists. Cut hole (off = fill) picks the direction: on, your stroke cuts a hole, and off, it fills one back in. The tool pill reads Alpha (cuts holes) or Alpha (fills holes) so you always know which way the brush is pointing.

Holes are how a cave mouth, a tunnel entrance or an interior below ground level becomes visible. A hole is a hole to the game as well as to the eye, so cut them where you mean to: there is nothing to stand on.

Conditional paint, the part worth learning

Under Advanced Paint and Brush Filters are the gates, and a stroke only touches a cell where every gate you have enabled passes. This is the feature that turns careful mouse work into two checkboxes.

Gate	What it limits the stroke to
Height Gate (m)	Ground between a Min and a Max height
Slope Gate (deg)	Ground between a Min and a Max steepness, in degrees
Gate by topology bit	Cells where a chosen Bit is set, or (with Require bit SET off) where it is clear
Gate by splat channel	Cells where a chosen Channel is above a Threshold, or with Match dominant channel on, where it is the strongest channel there

Replace dominant channel with a Source channel is the related tool: it repaints only where a particular texture is currently the dominant one, which is how you swap every patch of Grass on a cliffside for Rock without touching the Grass everywhere else.

The topology and splat gates also gate sculpt strokes, so “smooth only the sand” and “raise only the forest floor” work the same way.

What you see is what saves

The terrain shader reads the same layers you are painting, so a stroke and its undo both show up immediately, in the region you touched rather than by rebuilding the world. What you see in the viewport is what the .map gets when you save.

Painting the wrong layer is easy and quiet

The four layers share one brush and one set of digit keys, and Topology and Alpha both look like nothing is happening if you are not watching the right thing. Check the tool pill before a long stroke: it names the layer and the channel every time, which is faster than undoing thirty seconds of work on the wrong one.

Where each layer lives inside the map file is The map file and the sidecar, and what the generator writes into these same layers is How Rust builds a map.