5 Heightmap_Library

FeXoR edited this page 2016-05-18 11:45:37 +02:00

Table of Contents

• What is a heightmap?
• General heightmap functionality
• Erosion
• Painting terrain by height and inclination
• Local heightmap manimulation and window functions

The [heightmap]source:ps/trunk/binaries/data/mods/public/maps/random/heightmap library contains functionality for global heightmap/reliefmap manipulation for random maps.

What is a heightmap?

A heightmap or reliefmap is an array of map width +1 arrays of map depth +1 numbers. The values define how high a given vertex between terrain tiles is compared to the default water level (not that of the map!) in meters. By default the heightmap is stored in g_Map.height (see the map object in [map.js]source:ps/trunk/binaries/data/mods/public/maps/random/rmgen/map.js). The limits are given by the engine and are stored in [library.js]source:ps/trunk/binaries/data/mods/public/maps/random/rmgen/library.js of the more fundamental rmgen library:

• SEA_LEVEL The default water height of 20 meters (above the minimum value) that will count as 0 for the height values in the heightmap
• MAX_HEIGHT_RANGE The difference of minimum and maximum height values the engine allows, roughly 712 (values out of range will be cut to minimum and maximum value)
• MIN_HEIGHT The minimum value of a heightmap of -20 (not cut by the engine)
• MAX_HEIGHT The maximum value of a heightmap of roughly 692 Between those vertices the terrain tiles are placed (which is why there is one tile less in x/y direction then vertices). To get a better feeling for what one heightmap unit means for random maps: Terrain tile width = 4 meters.

General heightmap functionality

The file [heightmap.js]source:ps/trunk/binaries/data/mods/public/maps/random/heightmap/heightmap.js contains the fundamental tools to work with heightmaps.

• getMinAndMaxHeight Takes a heightmap and returns an object with properties min and max, the minimum and maximum height value present in a heightmap.
• rescaleHeightmap Rescales a heightmap's height values linear to have minimum and maximum as given by the arguments. ToDo: Add a height to be unchanged (e.g. the water height to preserve the costline) and rescale above/below that value seperately. Logarithmic/exponential scaling would also be nice with the base as parameter.
• getStartLocationsByHeightmap Searches a heightmap for a given number of points within a given height range and distance to the map border and tries to maximize the distance between the points returning them in a list.
• distributeEntitiesByHeight Places entities/actors randomly chosen from a given list in a specific height range while avoiding given points (e.g. start locations) and the map border by the given distance.
• setRandomHeightmap Sets a given heightmap to entirely random values. This is mainly meant for using erosion/smoothing on it later to get a realistic over all map shape (or test stability of erosion/smoothing functions)
• setBaseTerrainDiamondSquare A method to set a heightmap to a realistic shape within the given height range limits (they might not be reached though). The initialHeightmap defines the global shape. The smoothness parameter can be chosen between 0 (uniform in roughness on all scales so quite rough even at small scales) and 1 (roughness decreases with smaller scales exponentially so quite smooth on small scales).
• globalSmoothHeightmap Smoothes the heightmap depending on the adjacent tiles height. The strengthvalue should be chosen between 0 (no effect at all) and 1 (quite strong smoothing). To get an even stronger smoothing effect apply it multiple times (rather than increasing the strength above 1). This can be seen as a very simple erosion function (e.g. erosion by decay and gravity). To get directional effects an assymetrical smoothMap can be used (e.g. to simulate wind/sun driven erosion).
• rectangularSmoothToHeight Pushes the center of a rectangular region towards a target height while preserving the original height and shape at the edges.

Further planned functions: getTileCenteredHeightmap e.g. to paint tiles by height, getInclineMap a vector map e.g. for water driven erosion, getSlopeMap a scalar map e.g. for painting cliffs.

Erosion

WIP. It's planned to put (more complex) erosion functionality (like water driven erosion) in a separate file.

Painting terrain by height and inclination

WIP. A fully automated method to paint the whole map realistically will go here. It is planned to make use of the biome system (the current biome functions are not sufficient though).

Local heightmap manimulation and window functions

WIP. All global heightmap functionalities can be used locally by manipulating a partial heightmap and fuse that manipulated part back into the original heightmap with appropriate windows functions (that fullfill the boundary conditions).