infomation i can give other will have there own info . In the unreal games engine to paint environment you would use vertext painting .. vertex painting is not a complicated set up .. u can learn it within couple hour .. howver unreal engine does require decent spec pc
vertex pairing u cna paint grass mud rocks ect ... within 3 channles ... you have the rgb ref green blue channel ( similar photshop) ,,, you pain in those channels ( exmaple red channel one you can have grass . blue channel mud) thisb reak up tiling .........
another method was in video one enironemnt artist from naughtty dog ( said if there seam or area that texture was broken cover it with foliage an air vent ........ reason ther foliage there ,,,,.. to make it complete in every 3d application .... ( there each have there own rules .