AGS has the ability to import an external BMP or PNG file to use as the walkable-area, hotspot or walk-behind area mask. If you don't like the way you have to draw these in the editor itself, you can draw them in another program and then import them. This is also useful if you are converting a game you were making with another game-creation system into AGS.

To use the feature, click the "Import Mask" button (in the toolbar) in the relevant mode of the Areas editor. There are some restrictions to how this file must be drawn: it must be the exact same size as the background scene, and it must be in 16-colour (4-bit) or 256-colour (8-bit). Then, colour 0 on the bitmap signifies transparency and colours 1-15 are used as the respective hotspot/walk-behind/walkable area numbers.

IMPORTANT: Do NOT use any colour numbers above 15 on the mask bitmap. Use only palette indexes 0 to 15.