There are 2 maps of the same dimensions :
- a depth map, like in standard shadow mapping
- a color map, that stores the filtering colors
- the color map is filled with (1,1,1)
- the opaque geometry is rendered on the depth map only
- the transparent geometry is alpha-blended on the color map, reading the depth map.
The point is shadowed (depth test) ?
- Yes, return (0,0,0)
- No, sampling of the color map.
Since this shadow map stores the depth and the color filter of a light ray reaching an opaque geometry, it can be used on opaque geometry only.
I still use standard shadow mapping on transparent geometry, just taking into account the depth data of this shadow map.
Thank you so much for the help I got