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Procedural Terrain

Josh

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I wanted to add some default procedural generation tools in the Leadwerks 3.1 terrain editor. The goal is to let the user input a few parameters to control the appearance of their terrain and auto-generate a landscape that looks good without requiring a lot of touch-up work.

Programmers commonly rely on two methods for terrain heightmap generation, Perlin noise and fractal noise. Perlin noise produces a soft rolling appearance. The problem is that Perlin noise heightmaps look nothing like real-life terrain:

Image21.jpg

 

Fractal noise provides a better appearance, but it still looks "stylized" instead of realistic:

Image23.jpg

 

To get realistic procedural terrains, a more complex algorithm was needed. After a few days of experimentation, I found the optimal sequence of filters to combine to get realistic results.

We start with a Voronoi diagram. The math here is tricky, but we end up with a grid of geometric primitives that meet at the edges. This gives is large rough features and ridge lines that look approximately like real mountains:

f1.jpg

 

Of course, real mountains do not have perfectly straight edges. A perturbation filter is added to make the edges a little bit "wavy", like an underwater effect. It gets rid of the perfectly straight edges without losing the defining features of the height map:

f2.jpg

 

The next step is to add some low-frequency Perlin noise. This gives the entire landscape some large hills that add variation to the height, instead of just having a field of perfectly shaped mountains. The mixture of this filter can be used to control how hilly or mountainous the terrain appears:

f3.jpg

 

We next blend in some Fractal noise, to roughen the landscape up a bit and add some high frequency details:

f4.jpg

 

Finally, we use thermal and hydraulic erosion to add realistic weathering of our terrain. Thermal erosion works by reducing the harshness of steep cliffs, and letting material fall down and settle. Hydraulic erosion simulates thousands of raindrops falling on the landscape and carrying material away. This gives beautiful rivulets that appear as finger-life projections in the height map: Rather than relying on conventional hydraulic erosion algorithms, I created my own technique designed specifically to bring out the appearance of those features.

f5.jpg

 

Here is an animation of the entire process:

Animation1.gif

 

And in the renderer, the results look like the image below. All the parameters can be adjusted to vary the appearance, and then you can go in with the manual tools and sculpt the terrain as desired.

Image19.jpg

 

The new landscape has ridges, mountains, and realistic erosion. Compare this to the Perlin and fractal landscapes at the top of this article. It's also interesting that the right combination of roughness and sharp features gives a much better appearance to the texture blending algorithm.



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That's awesome! Now, what would be really cool is if this could be combined with an imported heightmap. E.g., if you use real-life elevation data, their resolution is typically too low for games (for SRTM data it's 30m per pixel in the US and 90m worldwide). So you have to "enhance" them to make them visually interesting, like adding some Perlin/fractal noise and eroding some of it afterwards.

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Nice Josh! Don't be afraid to throw in some crazy non realistic optional filters as well if you like. You could hide them under a seperate tab so people would know that they are special operations

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The final result is really impressive. Reminds me of Borderlands terrain; lots of playable plateau areas and realistic, sharp cliffs.

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  • Blog Entries

    • By Josh in Josh's Dev Blog 2
      I started to implement quads for tessellation, and at that point the shader system reached the point of being unmanageable. Rendering an object to a shadow map and to a color buffer are two different processes that require two different shaders. Turbo introduces an early Z-pass which can use another shader, and if variance shadow maps are not in use this can be a different shader from the shadow shader. Rendering with tessellation requires another set of shaders, with one different set for each primitive type (isolines, triangles, and quads). And then each one of these needs a masked and opaque option, if alpha discard is enabled.
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      { "turboShaderFamily" : { "root": "PBR.json", "OPAQUE": { "default": { "base": { "fragment": "Shaders/Blinn-Phong.frag.spv" } }, "isolines": { "base": { "fragment": "Shaders/Blinn-Phong_Tess.frag.spv" } }, "triangles": { "base": { "fragment": "Shaders/Blinn-Phong_Tess.frag.spv" } }, "quads": { "base": { "fragment": "Shaders/Blinn-Phong_Tess.frag.spv" } } } } } If you want to implement a custom shader, this is more work because you have to define all your changes for each possible shader variation. But once that is done, you have a new shader that will work with all of these different settings, which in the end is easier. I considered making a more complex inheritance / cascading schema but I think eliminating ambiguity is the most important goal in this and that should override any concern about the verbosity of these files. After all, I only plan on providing a couple of these files and you aren't going to need any more unless you are doing a lot of custom shaders. And if you are, this is the best solution for you anyways.
      Consequently, the baseShader, depthShader, etc. values in the material file definition are going away. Leadwerks .mat files will always use the Blinn-Phong shader family, and there is no way to change this without creating a material file in the new JSON material format.
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      I also was able to implement PN Quads, which is a quad version of the Bezier curve that PN Triangles add to tessellation.



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    • By Josh in Josh's Dev Blog 0
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