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<h4 class="subsubsection"> 4.10.11.1 General description </h4>
<p>To facilitate future improvements the plugin is split into several smaller
and communicating components
</p>
<ul>
<li>
Terrain system - defines cells, keeps track of loaded data, dispatch request
to the collision, rendering and data feeder parts.
</li><li>
Data feeder - provide height data on demand by either loading it from disk or
generating it by for example fractal algorithms.
</li><li>
Renderer - converts height data into triangles and feeds them into the rendering
pipeline, providing LoD, culling etc.
</li><li>
Collision system - do collision detection between height data and rays, segments
and triangles.
</li></ul>
<p>At current there are two implementations of data feeder, one renderer and one
collision system.
</p>
<a name="1"></a>
<h4 class="subsubheading"> Terrain System </h4>
<p>The terrain system is the central part in <samp>‘terrain2’</samp> plugin as it contains
definitions of cells as well as holding all other parts together.
</p>
<p>The main component in the terrain system is the <samp>‘cell’</samp>. Each cell within a
terrain system is a self contained area of the 2d map that contains its own
height map, material map, renderer-, feeder- and collision-settings. The
self-contained aspect is also related to that the cell is the unit used for paging
(on-demand loading and unloading) of terrain data.
</p>
<p>Each cell is defined by a small set of properties
</p>
<table>
<tr><td><p> Setting </p></td><td><p> Description
</p></td></tr>
<tr><td><p> gridsize
</p></td><td><p> Number of height points in each direction. Should be one more than power of
two (2^n+1) such as 129,257,1025. <em>CAUTION: For time being the grid must be
square</em>.
</p>
</td></tr>
<tr><td><p> position
</p></td><td><p> 3D offset in XZ-plane of cell relative to mesh center.
See more under coordinate systems
</p>
</td></tr>
<tr><td><p> size
</p></td><td><p> 3D size of cell in CS units. Defines the xz size as well as the max height
scale.
</p>
</td></tr>
<tr><td><p> heightdata
</p></td><td><p> Array of height data for each gridpoint, ordered left to right, top to bottom.
Other geometric properties of the landscape such as normal direction and tangent
plane is derived from the height data.
</p></td></tr>
</table>
<a name="2"></a>
<h4 class="subsubheading"> Coordinate system </h4>
<p>One important point to remember when dealing with terrain2 is the coordinate
spaces it use. There are two major coordinat spaces to keep track of, namely
<samp>‘heightmap space’</samp> and <samp>‘model space’</samp>.
</p>
<p>Heightmap space is the 2D coordinate space in which the heightmap is specified,
it has (0,0) in upper left corner of heightmap and x increase to the right while
y increase down. Most operations on cell level, such as
<samp>‘iTerrainCell::GetNormal()’</samp> and <samp>‘iTerrainCell::GetHeight()’</samp> operates
on coordinates in heightmap space.
</p>
<p>The second coordinate space is the 3d model space, which is the normal per
mesh-object coordinate space that all meshes in CS have. The transform between
model space and world space is defined by the iMovable of the mesh wrapper. All
rendering is in model space as well as some mesh global APIs such as HitBeam.
</p>
<p>The transform between heightmap space and model space have a fixed orientation
(rotation) while the linear components are set via the per cell size and offset.
</p>
<p><img src="usingcs/meshobj/terrain2coordspace.jpg" alt="usingcs/meshobj/terrain2coordspace">
</p>
<a name="3"></a>
<h4 class="subsubheading"> Renderer </h4>
<p>The renderer plugin is the most obviously visible plugin. It takes the terrain
height data and transforms it into a list of triangles for rendering and in the
process does such things as mesh simplifcation (LOD algorithms).
</p>
<p>In the current codebase of CS there is just one implementation of the rendering
plugin which is based on the "bruteblock" algorithm. Bruteblock works by dividing
the full cell grid into four quadrants, then continuing to subdivide those until
either the lowest subdivision level is reached or the LOD algorithm determins
there should be no more subdivisions.
</p>
<p>Bruteblock accepts a number of named parameters to control the LOD behaviour
</p>
<table>
<tr><td><p> Parameter </p></td><td><p> Description
</p></td></tr>
<tr><td><p> block resolution
</p></td><td><p> Block resolution in number of gridpoints. Should be power of two, other
values are rounded down. Default value is 16.
</p></td></tr>
<tr><td><p> lod splitcoeff
</p></td><td><p> Coefficient used in the calculation of per block lod level. Can approximatly
be interpreted as the distance to split in number of block-widths. Default value
is 16.
</p></td></tr>
<tr><td><p> splat distance
</p></td><td><p> Distance where to switch from material splatting to basemap rendering.
Passed on to the shader via the <samp>‘texture lod distance’</samp> shader variable.
Default value is 200.
</p></td></tr>
</table>
<a name="4"></a>
<h4 class="subsubheading"> Data feeders </h4>
<p>The data feeder is responsible for loading and pre-loading of terrain height
and material map data. There are two implementations, the simple and the threaded
data feeders. They both utilize the same loading code and properties however
the threaded feeder have the ability to preload data in the background at the
cost of some overhead and higher memory usage.
</p>
<p>The feeders take three parameters
</p>
<table>
<tr><td><p> Parameter </p></td><td><p> Description
</p></td></tr>
<tr><td><p> heightmap source
</p></td><td><p> File name of the heightmap data.
</p></td></tr>
<tr><td><p> heightmap format
</p></td><td><p> Data format in the heightmap source. Possible values are <small>IMAGE</small>,
<small>RAW8</small>, <small>RAW16LE</small>, <small>RAW16BE</small>, <small>RAW32LE</small>, <small>RAW32BE</small>, <small>RAWFLOATLE</small>,
<small>RAWFLOATBE</small>. The number specify the bit width, le/be little endian or big
endian. Default value is <small>IMAGE</small> which means the data is a image to be loaded
by the normal image loaders (such as a png image). <em>When loading a raw format
map, make sure to use the right format as no data validation is done. Invalid data
can cause your application to crash.</em>
</p></td></tr>
<tr><td><p> materialmap source
</p></td><td><p> File name of the material map data.
</p></td></tr>
<tr><td><p> offset
</p></td><td><p> Height offset value to add to height values after loading.
</p></td></tr>
</table>
<a name="5"></a>
<h4 class="subsubheading"> Collision plugin </h4>
<p>The collision plugin is responsible for doing collision detection between the
height map and triangles or segments/rays. There are currently just a single
implementation which use a variant of the digital differential algorithm to
compute the intersection points directly without having to triangulate the terrain.
The collision plugin have no properties.
</p>
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