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Creating 3D texture volume?

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Guest Anonymous Poster
if you mean creating the actual 3d texture data:
almost all procedural techniques can be done in 3d, or in 4d if you want it animated. Perlin noise and fourier synthesis work fine.

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quote:
Original post by Anonymous Poster
if you mean creating the actual 3d texture data:
almost all procedural techniques can be done in 3d, or in 4d if you want it animated. Perlin noise and fourier synthesis work fine.


Procedural is fine, but I want to make a texture, like in a graphics editing package (like photoshop)

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Guest Anonymous Poster
Well, that''s not so easy. You would need a graphics program that let''s you draw voxels instead of pixels... You could try to paint several 2D layers with a paint app, and then add them up to a 3D texture, but this will be _very_ time consuming, and a pain in the *ss to get them correlate correctly... It''s almost impossible to actually ''draw'' a 3D texture, and you can''t take scanned photographs either (unless you have a holographic camera Another source for 3D textures are tomographic scans, 3D texture mapping was initially developed to visualize CT''s.

But you can convert an existing 3D model into a 3D voxel representation (voxel rasterization). There are (very few) specialized software packages to do that (almost all of them SGI only and extremely expensive). You could try to write your own though. There is quite some info on the net, search for ''volumetric textures'' or ''volume visualization''.

If you want to do 3D texture mapping, stay with procedural textures

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Curiouse. That''s right, I''ve heard of USING 3d textures, but never MAKING them. What would you need it for? I can''t think of any truely useful uses. I wish to research this.

Alex Broadwin
A-Tronic Software & Design
-----
"if you fail in life, you were destined to fail. If you suceed in life, call me."
"The answer is out there."
"Please help, I''m using Windows!"

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quote:
Original post by ATronic
Curiouse. That''s right, I''ve heard of USING 3d textures, but never MAKING them. What would you need it for? I can''t think of any truely useful uses. I wish to research this.

Alex Broadwin
A-Tronic Software & Design
-----
"if you fail in life, you were destined to fail. If you suceed in life, call me."
"The answer is out there."
"Please help, I''m using Windows!"


Volumetric Fog, Per-Pixel lighting, Medical visuals, stuff like that

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Medical visuals yes. That''s what volumetric textures were made for. But what do YOU plan to use it for? The fog? If so, there are easier ways. I don''t think anyone really uses them for volume fog. Per-pixel lighting... how? I''ve never done it before, but I really would like to know.

Alex Broadwin
A-Tronic Software & Design
-----
"if you fail in life, you were destined to fail. If you suceed in life, call me."
"The answer is out there."
"Please help, I''m using Windows!"

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quote:
Original post by ATronic
Medical visuals yes. That''s what volumetric textures were made for. But what do YOU plan to use it for? The fog? If so, there are easier ways. I don''t think anyone really uses them for volume fog. Per-pixel lighting... how? I''ve never done it before, but I really would like to know.

Alex Broadwin
A-Tronic Software & Design
-----
"if you fail in life, you were destined to fail. If you suceed in life, call me."
"The answer is out there."
"Please help, I''m using Windows!"


I don''t really plan on really using 3D textures, I just want to mess with them a bit (for experence).

It''s not really per-pixel, more like per-texel...

ATI uses a 3D texture for a lightmap in this demo:
http://www.ati.com/na/pages/resource_centre/dev_rel/sdk/RadeonSDK/Html/Samples/OpenGL/RadeonDotProduct3.html

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To clearify the medical imaging software is not really that complex. Most of the newer software for CAT scans actually use SGI''s OpenGL. They mostly use the scanned image of chemical or electrical reactions in the body. Then map the intensity to a color, using base fractal methods they draw the image to the screen.

Such as a height map, you can choose a value range that will successfully demo the exact image data the computer sees. Using the fractal like methods to slowly bleed it into another color. This is easily demo''ed using a ".raw" type file and using it as hieght map then choosing the ranges that will best show your map. color the different heights and rendering to the screen

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Guest Anonymous Poster
Volume fog through 3D textures is extremly inefficient. There is a fundamental difference between 2D and 3D textures, lots of people oversee: if you draw a quad with a 2D texture on it, you can actually see the texture, but if you draw a 3D cube with a 3D texture on it, you won''t see anything but some single border texels. In order to visualize a 3D texture volume, you have to cut 2D polygonal slices through it, the more slices, the better the representation. For a 256*256*256 texture, an optimal number of slices would be 256 if viewed along a major axis. This is absolutely deadly for fillrate on anything else than Onyx-like workstations.
But, this effect can be used for lighting: imagine a 3D texture containing a gradient sphere (the 3D version of a glow). Now render any geometry with standard 2D textures as material and in a second pass with 3D texture coordinates while using a modulting blend. Here you go with an extremly cool full realtime pointlight effect. If you pre-raytrace shadows into the 3D texture, you can even have realtime shadow casting for free, but you''ll need a higher resolution 3D texture.
Last but not least: don''t underestimate the memory requirements for 3D textures: A 256*256 2D texture with one component takes 64kb, a 256*256*256 3D texture 16Mb !

-AH

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