Turtle Mountain

If you have ten minutes or so to spare I encourage you to check out this video. The rest of this post will be about how it was done:


The shyamalanian twist here is the guy lives in the back of a giant turtle. (Maybe not so much of a twist since the video title and thumbnail pretty much give it away.)

What you are seeing here is a new Voxel Farm system in action. It gets a very low-resolution mesh as a base and enhances it by adding procedural detail.

I think this is an essential tool for world builders.. Very often procedural generation deprives the creator of control over the large scale features of the terrain. Or, when control is allowed, it comes in the form of 2D maps like heightmaps and masks. There is no way to drive the procedural generation into complicated shapes and topologies like intricate caves, floating islands, wide waterfalls, etc.

We chose a massive turtle mountain to drive the point anything you can imagine can be turned into a detailed terrain. This is how it works:

The first thing you need to do is create a low-resolution mesh for the base of the terrain feature. This project used three of these meshes, one for the turtle's body and shell, another for the terrain protuberance on the top of the shell and one last mesh for a series of caves. Here you can see them:

On their own they were rather simple to produce. The tortoise is a stock model from a third party site. The mountain was done by displacing a mesh using a heightmap that had a fluvial erosion filter applied to it. The cave system mesh is a simple mesh with additional subdivisions and 3D noise applied to it.

These meshes were imported into Voxel Studio (our creative world building tool) and properly positioned relative to each other.

In addition to triangles, the meshes were textured using traditional means. Here you can see the texture that was applied to the turtle body:

Here is how the textured top mountain looks like:

Note how the texture uses single flat colors. Each pixel in the texture represents a terrain type, not an actual color. You can think of these as instructions to be passed down to the procedural generators when the time comes to add detail.

The meshes may appear detailed at this distance, but if you stretched them to cover four kilometers (which is the size of the turtle base in the world), you would see a single triangle span a dozen of meters or more. A single texture pixel would cover several meters. This would make for a very boring and flat environment. Here is where the procedural aspect kicks in.

Each color in a mesh texture represents what we call a "Meta-Material". I have posted about them before: here and here. In general a metamaterial is a set of rules that define how a coarse section of space can be refined. In this particular implementation for our engine, this is achieved by supplying two different pieces of information:

1. A displacement map
2. A sub-material map 

This is a very simple and effective way to refine space. The displacement map is used to change the geometry and add volumetric detail to an otherwise flat surface. The submaterial map registers closely to the displacement map so the artist can make sure materials appear at the right points in the displaced geometry. Once again the submaterial map does not contain final colors. Each pixel in this map represents a final voxel material that would be applied there.

Here you can see the displacement and submaterial map used for one of the metamaterials in the scene:

One particularly nice aspect of the system is that displacement properly follows the base mesh surface. It is possible to have nice looking cliffs and even apply displacement to bottom facing surfaces like the ceiling of a cave. For mesh-only displacement this is not usually difficult, but doing so in voxel space (so you can dig and destroy) can be quite complex. I'm happy to see we can have voxel cliffs that look right:

Metamaterials, beside displacement and submaterial maps, can be provided with "planting rules". This allows bringing in additional procedural detail in the form of larger instanced content. These can be voxel instances like the large rocks and boulders seen in the video or, they can be passed as instances to the rendering side so a mesh is displayed in that position. The trees in the video are an example of the later.

The previous image shows a mesh instance (a tree) at the left and a voxel instance (a boulder) at the right. Plants, grass, and small rocks are also instanced, but they are planted on top of materials, not meta-materials. One thing I did not mention before is this demo uses Unreal Engine 4. That is another key piece of tech that is coming along very nicely.

Already confused by these many levels of indirection? It is alright, once you start working with these features they begin to make perfect sense. More to that, it becomes apparent this is the only way you can get from a very coarse world definition into something detailed as seen in the video.

I hope you enjoyed this and that it gets your imagination started.