blending multiple shadow maps

#1

Hi im wondering if anyone could help me with this?

Im pretty new to lighting, but have been reading a lot
and watched tutorials. Im currently doing a project with depthmap shadows,
and have multiple spotlights to cover different smaller parts in my scene. So my problem is here
that the different shadows start to overlap, and some areas become darker than others.

How can i blend these shadow maps together so that my multiple spotlights can work together
and make one smooth and nicely lighted scene??

Hope my question is clear to understand, would be thankfull to get some help on this…

#2

I think I know what you mean. However as far as I know there’s no way around this. If you were to have two light sources in real life and the shadows of the two light sources crossed each other you would see a darkening where they intersect. So maya is just simulating what you see in nature.

One way to lessen the effect however is to increase the filter size on your spotlights. By default its set to 1 and the slider has a maximum of 5. But you can go well over this number by typing it in.

Increasing the filter size will blur your shadows but will also increase your render time.

#3

I’ve worked at 3 places now that have implemented there own version of this, we use it all the time where i work. The idea is you can focus the shadow maps for each object, and use static shadows for background and only dynamic on characters.

You’ll probaby need to look into writing your own shader though. I wrote a basic RSL shader a while back to do it, just load each shadow map in and min them together, then you dont get any werid overlap.

Nicko

#4

i see, thanks a lot for answers. Ill try and experiment abit with it.

Do i have to write my own shaders to focus shadow map for each object? Cause i never
touched on that. But if its possible to go around, how do i focus the shadow map?
Could this work with some sort of light linking??

#5

Use a seperate shadow camera. Pretty well every package lets you do this out of the box (eg mental ray for maya, 3delight for maya, rms ect)

#6

and have multiple spotlights to cover different smaller parts in my scene. So my problem is here
that the different shadows start to overlap, and some areas become darker than others.

Well that depends just what your doing > using multiple shadows piped through one light or are you using your spot lights to light various objects. If your using the latter just using object masking in your lights.

b

#7

thanks a lot for answers, its been helpfull. Ill see where i get from here

#8

If the scene and shaders aren’t too complex with reflections,refractions etc… and the number of shadow maps aren’t too many, you could try compositing the shadows in post.

Have one pass for your key light source and a separate pass for each shadow. In your compositing program you can combine all the shadows and multiply (or use it as a mask) on top of your key light pass.

#9

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