Starting to add terrain

Here is something that I felt was long needed- the ability to render terrain from height maps. I finally got around to making a simple class for one (based on Riemer’s XNA example). Thought it’s far from perfect it’s a decent start. Heightmaps are currently only generated from imported grayscale images, and always at full resolution. They use different shaders than the other objects, but made adaptable for deferred rendering. Consequently, they are also rendered in their own Draw function.

So there’s not much to the terrain right now. I just picked a texture and went with it. Instead of grass, which is commonly used, in my first attempt I decided to make a simple desert scene with a sand texture.


The original color of the sand looks too strong, making the landscape look somewhat alien, which is not what I’m looking for. I went into Photoshop to improve the texture’s brightness and contrast, and tried the result.


At least the ground looks a lot better now. With the help of some XNA sample project code, I made the Dude model walk on the surface of the terrain. This screenshot also shows the tri-planar mapping that I applied to stop textures from stretching on steep surfaces. Here’s a video of the terrain after having made those fixes. (The disappearing dude problem has since been fixed, it was a matter of correctly creating a bounding sphere for it).


The tri-planar mapping was surprisingly simple to apply. These two articles give a good explanation of how it works.

While the Dude is skating and moonwalking all over the surface, it’s not a true physics feature, because there’s no real constraints like stopping him from walking on steep slopes or passing through other objects. But it would be useful for placing objects on the ground.  As it is, though, I might as well release this game as “Big Rigs: Dude Edition” and accept the consequences. (At least I clamped the heights at the terrain edges so the character doesn’t spazz all over the place!)

From here I’ve realized that optimizations for heightmaps are greatly needed for many cases. I’m using a 512×512 image for the terrain, which end up being a lot of triangles for the vertex buffer. Previously I mentioned how rendering a bunch of geometry is my newfound bottleneck from instancing many objects- well, now it’s in the terrain. My light pre-pass rendering has dropped to 25-30 FPS, and deferred rendering at 40-50 FPS. Also, these framerates are without rendering it in the shadow maps! I can’t imagine how much slower it will be if I did render the terrain for self-shadowing. As of now, it looks decent without self-shadowing. As I further work on the scene culling (it currently does brute-force culling for instances), the terrain rendering will improve as I gradually adapt the culling techniques.

Breaking the terrain into chunks is a an obvious improvement, which would work just with brute-force culling. But quadtress and LOD meshes are the goal here. I looked at ROAM-based techniques for LOD rendering and it looks pretty good, but I think I will use geometric clipmapping, which looks easier to understand implement.

My approach will be starting out just with a simple, 2-level geo clipmapping scheme, rendering a small chunk of terrain around the camera at full resolution, and the outer clipmap at 1/2 the detail of the original. The sample terrain I’m using is not too big (513×513) so using more than 5 levels seems like overkill. However, I plan to eventually get larger terrains working, for over 4 square kilometers. The reason for that is, well, I already have a game in mind for it 🙂 I will be developing it together with the engine.


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