The up-coming I3D conference on interactive 3D Graphics and Games will
feature several interesting papers. I have found one of these paper
called “Fourier Opacity Mapping”, proposed by Jon Jansen and Louis
Bavoil, very interesting. I could not resist implementing this nice
Fourier Opacity Mapping (FOM) is about approximating light attenuation
through a volume made of particles for the purpose of volumetric shadow.
Let’s consider a spot light: the authors propose to reconstruct the
light transmittance function along each ray using a Fourier series. The
coefficients of the Fourier series are stored in the fourier opacity map
in light view space. This map is generated using usual particles
rendering with transformation in the Fourier basis of absorption
coefficients in the fragment program. Then, when rendering the particles
from the camera view, the correcte light attenuation can be recovered
for each particle. I will not go into the details here. You can read
this nice paper here or my report on
my personal webpage. You can also
find open a demo with source code. (You will need a recent video card to
run the demo since it uses GLSL 1.5 and render data into 6 buffers in
This method is really efficient to simulate colored light attenuation
when passing through a volume of particles. Furthermore, if you want an
exemple of good use by skilled artists, just have a look at the game
Batman Arkham Asylum which features this method.
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I saw it on your blog, great job!
Thank you very much! :)