Having worked on a couple of open world titles, I’ve had experience with two different teams methods of creating the basic surface mesh of a game wold. They both used at their core, a flat mesh that was deformed in a vertical axis by artists or imported height map data.
Texture mapping co-ordinates were projected along the same vertical axis as the mesh was deformed. This meant that the greater the slope of the mesh, the more distorted the texture appeared in the world, as is illustrated by the image below,
Even when painting an alternate texture on these steep areas, or increasing the density of the terrain mesh the stretching of the texture was an obvious problem.
The solution to this problem, in both cases involved artists creating custom meshes for specific locations, or generic ‘cliff’ meshes that could be placed in the world to obscure the worst cases of terrain distortion. I’ve noticed this method used in many titles since becoming aware of it, seemingly the de facto formula that game developers come up with.
The constant march toward graphical perfection demands a better solution, one that allows a terrain artist to create a better result with the same or less time spent doing so.
While playing through Red Faction Guerrilla released in June 2009, i came to appreciate that the team behind it Volition Inc, must have developed a method i’d not noticed before that game.
It appears that the Red Faction terrain mesh is receiving mapping co-ordinates from all 3 axes, X Y & Z. This solves the main issue, as seen above, steep surfaces are mapped with no stretching. However there is more to this solution than first meets the eye. In order to blend seamlessly between two different axes, they must overlap, and fade out just as they start to stretch.
After all the effort required to build such a complicated terrain blending system, i imagine the editor software had some neat tricks, the game terrain could have easily had a base selection of textures, and rules that meant as an artist distorted a section of terrain higher or lower, the steep sides would fade to a rocky / cliff surface.
This solution has not solved all cases, as there are still unique meshes placed within the game world. It is impossible to create undercuts as the terrain is being displaced along the vertical axis only. Still the terrain in Red Faction Guerrilla is the most impressive example I have noticed in a released title.
The most recent trailer for the upcoming RAGE shows a few glimpses of the terrain in that game, which looks to be a step beyond the bar set by Volition this year.
