The terrain layer has several modes and the top two are the ones you use. Isometrical is the default: it lays terrain in diamonds and blends the edges for you. Tidy, but it cannot make a square edge.
Rectangular lays one tile per square, and what goes in it is picked at random from the same family - "family" meaning everything that appears when you open the Subtile window and Ctrl+Left-click that terrain. So you get square shapes, and painting the same spot twice gives you different tiles each time.
In either mode you do not have to pick from the list on the left: hold the cursor over terrain you want and Ctrl+Alt+Left-click makes it the brush. It is an eyedropper.
Where the two part company is not ordinary terrain but obstacle terrain and doodads.
| Isometrical · 장애 지형 | Only lays properly at brush size 1. At 2 or more it shreds the terrain you already made. |
|---|---|
| Isometrical · 두다드 | Does not lay at all - not even null terrain. Nothing happens. |
| Rectangular · 장애 지형 | Lays, randomised. |
| Rectangular · 두다드 | Lays, randomised. |
| Rectangular · 브러시 크기 | Works above 1x1. |
To use a doodad this way it has to be in terrain state: a doodad in doodad state will not copy. Copy and paste a piece of the doodad first, then use that as the brush.
This is the fastest way to make a floor look laid by hand. Scatter obstacle terrain or doodad pieces with a large Rectangular brush and every square gets a different tile, which takes away the repeated-tile look of something stamped out.
Why the row decides the behaviour comes down to the shape of a tile number. The map stores two bytes per tile: the upper bits are the group and the low four bits are which of that group's sixteen megatiles it is - so a group holds sixteen, and what looks like one row in the palette is one group. The properties are defined per group, in CV5, while walkability and height are defined per minitile, in VF4. Which is how terrain can look perfectly fine and be unwalkable.
Black (null) terrain is not one thing either. Which row of the palette it came from decides its behaviour - the column does not matter. Null from the creep row lets ground units stand on it and Zerg buildings land, but not Terran ones; null from a buildable row takes both kinds of building but no ground unit; null from an unbuildable row takes none of the three. The properties are defined per megatile group, which is a row.