...a quickly hacked together terrain multitexturing editor i did a while ago...

-> terrain_editor.zip ~ 3mb

(shift+) cursor keys - fly around
rmb - rotate camera
(alt+) lmb - draw into the blue channel of the terrain macro map
s - save macro map
1 - display alpha channel
2 - display blue channel
3 - display multitextured terrain

because of a bug in pixel_to_vec i don't have the necessary control over the alpha channel so the tool is buggy and quite useless!