Combine3 Specular Mapping With Dotproduct3
Bump mapping and 3D Lightmapping on the Radeon®
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The RadeonCombine3SpecMap sample uses ATIX_texture_env_combine3,
ATIX_texture_env_route,
EXT_texture_env_dot3,
ATI_texture_mirror_once,
ARB_texture_cube_map,
and EXT_texture3D
to demonstrate per-pixel lighting effects possible in
OpenGL®. It demonstrates Combine3 Specular Mapping,
DOT3 Bumpmapping, and 3D Lightmapping. For more information
on the DOT3 Bumpmapping and 3D Lightmapping techniques
employed by this demo, see the Dotproduct3
Bump Mapping with 3D Lightmapping demo.
For more on 3D light mapping as well as 3D texturing in
general, check out the Radeon®
3D Texture Mapping Tutorial.
Here is the basic idea behind this demo:
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3 pass algorithm for performing realistic lighting.
PASS 1 : calculate attenuation via 3D light map
using ATI_texture_mirror_once extension.
PASS 2 : diffuse lighting with DOT3 bump mapping
(EXT_texture_env_dot3) and cube map normalization.
PASS 3 : specular lighting (using ATIX_texture_env_combine3
and ATIX_texture_env_route) and cube map normalization.
[(AMBIENT + (N.L)*BASE_MAP) + (N.H)k]*ATTENUATION
PASS 1 = ATTENUATION
PASS 2 = PASS1 * (AMBIENT + ((N.L)*BASE_MAP))
PASS 3 = PASS2 + PASS1*(N.H)16
Figure 1 shows the final result.
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Figure 1 - Final Specular Map
with Dot3 Bumps and 3D Lightmap
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Pass 2 begins by taking the vector from each vertex
to the light converting it into tangent space (the coordinate
space of the base texture). We use a cube map for vector
normalization with the light vector placed in the texture
coordinates. These coordinates are used to reach into
a pre-computed cube map in which each face of the cube
contains a normalized vector pointing outward from the
center of the cube. The results of these computations
are shown in Figure 3. The dot product of this
light vector and a pre-filtered height map (the normals
in texture space, shown in Figure 4 as color) is
computed using ATIX_texture_env_dot3 to produce the diffuse
lighting term (N.L). Figure 5 shows the results
of the DOT3.
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Figure 2 - Result of 3D lightmapping
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All of this is then modulated with the Basemap (Figure
6) and the results from pass 1 (attenuation term shown
in Figure 1).
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Figure 3 - Light Vector displayed
as color
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Figure 4 - Pre-filtered height
map
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Pass 3 begins by taking the vector from each vertex
to the viewer converting it into tangent space (the coordinate
space of the base texture) and calculating a halfway vector.
We use a cube map for vector normalization with the halfway
vector placed in the texture coordinates. These coordinates
are then used to reach into a pre-computed cube map in
which each face of the cube contains a normalized vector
pointing outward from the center of the cube. The dot
product is then found between the halfway vector and the
normal vector (as stored in the height map Figure 4).
We now have our specular term (N.H) and we raise it to
the 16th power using an approximation ((N.H)2 - 0.75)*2.0);
this is done with the help of ATIX_texture_env_combine3
and ATIX_texture_env_route. We now have our specular map
(shown in Figure 7). This is then modulated with
the results of pass 1 and then added to the results of
pass 2. The final image is shown above (Figure 1).
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Figure 5 - Results of DOT3 between
light vector and heightmap
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Figure 6 - Base Texture
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Figure 7 - Specular Map
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- RadeonCombine3SpecMap Controls
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- M - Show stages of bump,lightmap and spec. map
process
- T - Cycle through the different textures
- V - Toggle display of light per-vertex vectors
- H - Toggle display of halfway per-vertex vectors
- C - Toggle display of tangent space per-vertex
coordinate systems
- W - Toggle display of wireframe
- [UP] - Move light further from object center
- [DOWN] - Move light closer to object center
- [LEFT MOUSE] + Mouse - Rotate Object
- [RIGHT MOUSE] + Mouse - Rotate Light
- [SPACE] - Stop light motion
- [ESC] - Quit
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Downloads
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Note: The source code and media should be unzipped
into the following recommended directory structure to
ensure you can easily compile and run the executable.
Radeonxxxxxx.zip -> x:\atiddk\OpenGL
RadeonCombine3SpecMap.zip
Back
to Samples Page
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