Game Rendering » Terrain

Terrain Texturing with Texture Splatting

admin — Sat, 11 Oct 2008 23:32:23 +0000

The old way to do splatting was to assign a texture for each triangle/quad in the terrain and then let GPU create the fading between the different textures. The following link is to one of the most famous descriptions of such an technique:

http://cbloom.com/3d/techdocs/splatting.txt

The drawback with the method is that is uses fillrate a lot as each triangle is drawn multiple times to archive the fade. Therefore new methods with shaders or multitexturing is to prefer.

Many games uses nowadays alpha maps together with terrain textures to do splatting. The alpha map decides where the texture should be splatted to the terrain. For each texture that should be used on the terrain, one texture channel is needed for the alpha map. The size of this texture determines the quality/resolution of the transitions between different types of textures on the terrain. Below is and example of a such alpha map and how it looks like in a game.

To the left is the textures used, notice how low resolution they are allowed to have. To the right is one of the alpha maps (for the dark grass).

Render of the terrain with splatting in jMonkeyEngine:

In the following link is a comparision of using a single large texture to cover the whole terrain versus using splatting of a few small textures.

http://mikescodeblog.blogspot.com/2007/11/3d-landscape-rendering-with-texture.html

The game Sid Meier’s Railroads uses a kind of splatting that is either vertex or quad based. Their maps consist of a single texture where each pixel in the texture has a colour that is connected to a specific terrain texture. This allows for a large amount of different textures for the terrain in the same map, but limits the type of fading between different textures.

Here’s a screenshot of how the maps in the game Supreme Commander are created. The game uses splatting and can only handle five different textures. One is the base texture and fills up where no other texture are. The rest of the four texturelayers requires alpha maps and they are saved in a single RGBA texture. The shot below shows how beautiful splatting can be when implemented correctly. The water is only height dependent and is therefore not splatted.

The source of the image is the following tutorial of how to make maps for Supreme Commander:
http://supcom.wikia.com/wiki/Height-_/_Texturemaps_with_image_editing_tools

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Mega Textures

admin — Sat, 11 Oct 2008 23:21:51 +0000

Instead of the normal way of texturing with tiled images and trying to blend different types of textures together this approch uses one big texture that covers the whole terrain. Because of the size needed for the texture, some smart mipmapping and also compression of the data is needed. The big advantage above the other methods seems to be that this enables the artist to draw the terrain however she likes. There are simply no limits of the number of textures that can be used in the final mega texture.

Link to more in detail description of the method:
http://www.beyond3d.com/content/articles/95/1

A similar method called Sparse Virtual Texturing:
http://silverspaceship.com/src/svt/

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Hill Terrain Generation

admin — Sat, 11 Oct 2008 22:56:53 +0000

One way to generate a terrain heightmap is to generate a number of random hemisphere shaped hills with random radius on random coordinates and blend the them all together. By setting a min and max radius the final look can be tweaked to something you like. The result might look like the following:

Link to more detail about the algorithm (also the source for the image):
http://www.robot-frog.com/3d/hills/hill.html

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