avolkov
809efd28a3
git-svn-id: svn://svn.code.sf.net/p/sc2/code/trunk@1367 8092fc87-c524-0410-9efc-e669fe64eaf9
55 lines
2.8 KiB
Plaintext
55 lines
2.8 KiB
Plaintext
Planet surface rendering code
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The way the planets appear on the screen (based on planet type
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definition in plandata.c) is determined by several factors:
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1. Topography algorithm (PlanetFrame.Type)
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2. Color map (PlanetFrame.CMapInstance)
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3. Elevation -> colormap index xlat table (PlanetFrame.XLatTabInstance)
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4. Base elevation (PlanetFrame.base_elevation)
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5. Several others not covered here: faults, craters (blemishes)
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First, the planet topography is generated according to the algorithm
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selected for the planet: TOPO_ALGO, CRATERED_ALGO, GAS_GIANT_ALGO.
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TOPO_ALGO and CRATERED_ALGO use a fractal algorithm to pseudo-randomly
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generate a surface, then 'craters' are added and, at the end, the map is
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dithered for CRATERED_ALGO. GAS_GIANT_ALGO is of course different
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because it needs to produce a series of ring-like structures with
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'storms' added at the end.
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The topographical map is a rectangle with each pixel representing an
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elevation level relative to 0, so the topography is expressed in terms
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of elevation relative to base elevation. Base elevation is applied to
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the generated map. Topography is created with elevations -128..127,
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and base elevations, currently, range from 100 to 200 (plandata.c) for
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normal worlds and are always 29 for gas giants. Since the gas giants
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do not have a real topography or a surface to speak of, their surfaces
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are rather simulated with elevations.
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At this point, the elevation levels are translated to the actual colors
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using the xlat table and color map. First, the elevation is translated
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to an index into the colormap using the xlat table (.xlt files), and
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after that, the actual RGB color is drawn from the colormap (.ct files)
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at this index.
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There are 3 colormaps per instance specified in PlanetFrame. The active
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colormap is selected from these 3 based on the surface temperature of
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the planet: cold, normal and hot. The framework is also laid down for
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3 xlat tables (one per surface temperature), but, AFAIK, distinct xlat
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tables are never actually used. Currently, there is only 1 xlat table
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per instance in each file.
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The colormap files (.ct) seem to be in original DOS format. Probably
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because they do not translate to the CLUT system very well. The colormaps
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are carefully crafted and synchronized across all planet types to make
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the entire system function properly. They are composed of 4 gradients of
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different hue, 32 colors each (4*32=128 colors). Gradients go from the
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most intense color to near black. For the most planet types, the three
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colormaps per instance are all the same, so that the way a planet
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surface looks does not change with the surface temperature. Notable
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exceptions are: h2o_cts_ (water world) and mtl_cts_ (metal world); there
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could be others as no byte-identical examination was done.
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See blue-gas-giant-pal.png for an example colormap.
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