Maya 6.5 / detail shadow maps

[dropthatnow]

Hi,

I try to use detail shadow maps to calculate self shadowing for a fluid container. does anybody know if it is possible to do that at all ? are volumes and detail shadow maps supported at all ?

thx

[pberto]

selfshadowing is handled by the volume shader (in your case the mayabase maya_fluidshader behind the fluidShape node that you see in the Maya UI) in conjunction with a surface shadow shader.

even in the shadow casting case, (eg to get shadows of a cloud casted onto an underlying plane) you cannot use detail shadow maps if volumes are involved: detail shadow map rely on the rasterizer for computation and cannot make any assumption about the volume properties.

so use the raytracer and raytraced shadows.

detail shadow maps are good with the scanile and rasterizer algorithm, for non raytraced effects.

paolo

[dropthatnow]

thanks paolo !
that indeed sheds some light on why it didnt work as I expected. I assumed that mental rays implementation of deep shadow maps would work the same like in renderman. well, bad luck.
At the moment we work on a shot were the camera goes from earth orbit (a few 1000 km) down to the northpole ending 40m above ground in one shot. Obviously the director wants some clouds to fly thru. My choice for 3d clouds was maya fluids. As the clouds dont need to have any movement by themselves I thought there might be a way to kind of "bake" the selfshadowing into the clouds. that would drastically decrease rendertimes (I guess). Up to now one frame 2k/1.85 renders about 2 hrs.
Do you know if it is possible to store something like a photon map in fluid volumes ?

thx again!
s

[pberto]

no, there is currently no photonic counterpart for the fluid shader.

if you cannot afford to spend such rendering time,
you could try to "fake" the selfshadowing and avoiding the use of grids by just using the internal texturing, for instance with a Y color gradient that mimics it.

but one example is better than 1000 words: check the fluid examples in the visor:

visor> fluid examples> clouds&fog> FasterClouds.ma

then select the cloudLayerShape node which has notes for this trick written by Duncan Brinsmead.

I am trying to imagine your shot and I think you can manage to use it.
Lemme know,

paolo

[dropthatnow]

hi paolo.

I tried faking self shadowed clouds but I got a very defined light direction (moonlight, coming from a low left. settings in the fluidShape node are: 0 0.05 -1.000) and it . I already use the internal fluid light as it is much faster.

thx.