The advanced terrain engine uses a height map split up into blocks of 100 by 100 metres. Each block consists of height and texture information, normals, a hole map and LOD information.

Texturing is done by blending multiple textures layers together, each texture layer has its own projection angle and blend values for blending with other texture layers. The resolution of the blend values is configurable per space and the layers themselves are stored per chunk. The textures are assumed to be rgba with the alpha channel used for the specular value.

The lighting of the advanced terrain is performed per pixel. A normal map is stored per block, which is used in the lighting calculations, this is combined with the blended texture to output the final colour. The terrain allows up to 8 diffuse and 6 specular lights per block. For details of how the specular lighting is calculated see Terrain specular lighting

The terrain uses a horizon shadow map for shadowing, this map stores two angles (east-west) between which there is an unobstructed view of the sky from the terrain. In the terrain shader, these angles are checked against the sun angle and the sun light is only applied if the sun angle falls between the horizon angles.

The purpose of the LOD system is to reduce the amount of cpu and gpu time spent rendering terrain and to reduce the memory footprint of the terrain. The terrain LOD system achieves this by reducing geometric and texture detail in the distance and loading/unloading high resolution resources as they are needed. The LODing is broken up by resource so that texture and geometric detail can be streamed separately. The LOD distances are configurable in the space.settings file, please see terrain section in space.settings for more information.

Since the advanced terrain allows for a number of configuration options the memory footprint of the terrain depends on the options selected.

In the Fantasydemo example provided, the terrain overhead is as follows (this information was captured using the resource counters in the Fantasydemo client, the graphics settings were set to high and the far plane was set to 1500 metres):

(this includes the textures used by the texture layers, which may also be used by other assets)

Terrain memory usage

A terrain2 section is contained in a chunk's .cdata file. It contains all the resources for the terrain in a chunk. The different types of terrain data are described in BNF format in the following chapter.

<heightMap> ::= <header><heightData>
<header> ::= <magic><width><height><compression><version><minHeight><maxHeight><padding>

<textureLayer> ::= <header><textureName><blendData>
<header> ::= <magic><width><height><bpp><uProjection><vProjection><version><padding>
<textureName> ::= <length><string>

<normals> ::= <header><data>
<header> ::= <magic><version><padding>

<holes> ::= <header><data>
<header> ::= <magic><width><height><version>

<shadows> ::= <header><data>
<header> ::= <magic><width><height><bpp><version><padding>

<dominant> ::=<header><texNames><data>
<header> ::= <magic><version><numTextures><texNameSize><width><height><padding>

The terrain section in the space.settings file contains the configuration options for the terrain. The values in the lodInfo and server sections can be modified, but the root level values should only be modified by the World Editor.

    <version> 200 (int) </version>
    <heightMapSize> uint </heightMapSize>
    <normalMapSize> uint </normalMapSize>
    <holeMapSize> uint </holeMapSize>
    <shadowMapSize> uint </shadowMapSize>
    <blendMapSize> uint </blendMapSize>
    <lodInfo>
      <startBias> float </startBias>
      <endBias> float </endBias>
      <lodTextureStart> float </lodTextureStart>
      <lodTextureDistance> float </lodTextureDistance>
      <blendPreloadDistance> float </blendPreloadDistance>
      <lodNormalStart> float </lodNormalStart>
      <lodNormalDistance> float </lodNormalDistance>
      <normalPreloadDistance> float </normalPreloadDistance>
      <defaultHeightMapLod> uint </defaultHeightMapLod>
      <detailHeightMapDistance> float </detailHeightMapDistance>
      <lodDistances>
        +<distance?> float </distance?>
      </lodDistances>
      <server>
        <heightMapLod> uint </heightMapLod>
      </server>
    </lodInfo>    

The terrain is a huge height map defined by a regular grid of height poles, every 4x4 metres. Terrain is organised into terrain blocks of 100x100 metres. Each of these blocks can have up to four textures, which are blended on a per-vertex (i.e., per-pole) basis. The terrain also is self-shadowing, and allows holes to be cut out of it, for things like cave openings. The terrain also contains detail information, so that the detail objects can be matched to the terrain type.

The terrain integrates properly with the chunking: each terrain block is 100x100 metres, which is the size of the outside chunks. The terrain blocks are stored in separate files, so that they can be opened as needed.

Each terrain block covers one chunk, each with dimension of 100x100 metres. It contains 28x28 height, blend, shadow, and detail values (there are two extra rows and one column to allow for boundary interpolation). Each terrain block also stores 25x25 hole values, one for each 4x4m tile.

The table below display the terrain cost per chunk.

Terrain cost per chunk

For example, for a 15x15 km world the total disk size of the terrain would be: 10,017 x 150 x 150 ~ 215MB.

With a field of view of 500m, and each terrain block covering 100x100 metres, a typical scene would require roughly 160 terrain blocks in memory at any one time.

The memory usage of this much terrain is about 2MB, plus data management overheads.

The TerrainTextureSpacing tag included in the environment section of file <res>/resources.xml (for details on the precedence of entries in the various copies of file resources.xml, see File resources.xml) determines the size (in metres) to which texture map will be stretched/shrunk when applied to the terrain.

This value determines both the length and height of the texture tile.