Open indexed PNG files and export them into Westwood 2D terrain tile files.
More info on this wiki page: https://github.com/OpenRA/TilesetBuilder/wiki
Enter those commands in a command line:
git submodule init
git submodule update
cd OpenRA
make all
cd ..
make
If you don't use git, put engine version 8596ce00cc27c3cc2ee4cd899465793ab7b5faa0
inside the "OpenRA" folder.
Then build the engine and run the make
command in the TilesetBuilder directory.