Modifiers
Modifiers are similar to those in software like Blender. You add these to your GeneratorSettings, and they get applied after the generation is finished, giving you varied results and possibilities. You can think of them this way: each cell in the grid is checked, and if it meets a certain condition, it will get modified (deleted, replaced with another TileInfo or a TileInfo will be placed in the same spot on a different layer).
Note
In Gaea, the modifiers' array order matters. Modifiers get applied in this order, so different sequences can give different results.
Filtering
Modifiers can be filtered. This means it will only modify certain tiles.
-
filter_type: can beNONE,BLACKLIST,WHITELIST, orONLY_EMPTY_CELLS. -
filter_ids: inBLACKLIST, it will NOT attempt to modify tiles with anidthat can be found in this list (ids are strings that make identifyingTileInfos easier, see Gaea's Resources).WHITELISTwill invert this logic. For example, using aNoisePainterto only place gold ore in tiles with theid"/..one". -
filter_layers: it will only check in these layers for theids mentioned above or, iffilter_typeisONLY_EMPTY_CELLS, for an empty cell. Leaving this array empty, the filtering will check for all layers.
All Modifiers
There are a few modifiers in Gaea at the moment:
Generate Borders
Generate border tiles around already placed tiles.
Fill
Fills the full rectangle of tiles.
Using Fill to generate autotiled walls around a WalkerGenerator's generation.
Carver 2D/3D
Carves holes into the map using a noise texture.
Smooth
Smoothes the map using Cellular Automata.
Walls
Adds tiles to those below already placed tiles that aren't the Generator's default tile.

In this example, the walls are added after both the floor and ceiling (using the Fill modifier) are added, giving the dungeon a different perspective.
An example without the Walls modifier looks like this:

Noise Painter 2D/3D
Replaces tiles in the map with another tile based on a noise texture and a threshold.
Heightmap Painter 2D/3D
Replaces tiles in the map with another tile based on a noise heightmap.
Remove Disconnected
Uses flood fill to remove all tiles that aren't connected to starting_tile.
Advanced Modifier 2D/3D
Lets you basically make any modifier you want. Has a list of conditions. Every cell it tries to modify, it will check that all conditions are met, and only then will it (re)place that cell with the chosen TileInfo. See the tutorial on how to use it.