This post shall help to unterstand better how textures are used in Celestia.
general informations:
- Supported file formats: JPG, PNG, BMP(not recommend), DDS (DXT1c, DXT1a, DXT3, DXT5). Not every grafic card support texture compression therefore check if you can use DDS files.
- Texture dimensions need to be powers of two.
- usual texture dimensions: 1k = 1024x512, 2k = 2048x1024, 4k = 4096x2048, 8k = 8192x4096, 16k = 16384x8192
Which file formats should be used for which map type?
standard texture: JPG, DXT1c, PNG, DXT3
- the alpha channel of PNG and DXT3 can be used for specular reflection.
specular map: JPG, PNG, DXT1c
bump map: JPG, PNG
normal map: PNG, JPG (if only low compressed), (DXT3, but some artifacts)
night light map: JPG, PNG, DXT1c
cloud map: PNG, DXT5
Note:
-Bump maps, normal maps and specular maps works only on modern grafic cards.
-A normal map is a special version of a bump map which is direct used by the grafic card.
More information about map types, it's function and the solarsys.ssc can be found here:
http://members.fortunecity.com/guilpain/index_uk.htm
How is a map installed?
1. Copy the map file into the medres, hires or lowres folder (c:/program files/celestia/textures/). Which folder exact doesn't matter but Celestia tries to load the texture first from medres, then lowres and at least hires the folder. A resolution switch with "shift+r/r" change this order. Of couse the resolution switch makes only sence if the textures are correct placed.
2. Edit the solarsys.ssc (c:/program files/celestia/data/) with notepad or an other editor and enter the map file name at the right position.
How much memory (ram) is needed to use a large textures?
The table shows the peformance dependent on the system memory.
Notes:
- The table is only a clue.
- The values assume that a prober grafic card is used (e.g. 64mb: TNT 16mb, 256mb: GF2 64mb).
- This table is valid for Windows9x. For other (newer) operating systems it's better to increase the memory.
- For a fly from object to object with fast load times there is more memory needed.
- Also with enougth memory there is a significant first load time for large textures.
Now a little bit math:
How many memory space (ram) need a texture?
JPGs and PNGs are small on the hard disc but grafic cards can't process this formats therefore the size of this file formats is in the memory essential more large. The following values for JPG/PNG are valid for texture compression off.
JPG / PNG
1K: 2,66mb
2K: 10,7mb
4K: 42,6mb
8K: 170 mb
DDS DXT1
2K: 1,33mb
4K: 5,33mb
8K: 21,3mb
16K: 85,3mb
DDS DXT3, DXT5
2K: 2,66mb
4K: 10,7mb
8K: 42,6mb
16K: 170 mb
Now an example with earth (the moon must be also regarded because it is visible if you turn the earth):
Note:
- For the best performace all actuel used textures should find place in the texture memory of the grafic card. This simple example shows also that a GF4 with 128mb can get a little bit stress.
- Other parts of Celelestia, other runing software and the operating system need also memory space!
Sorry my english is not the best ;-)
Jens
