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  Tutorials 3D Graphics Tutorials Fake Caustics

Fake Caustics

Shawn Hempel Tutorials Jul 29, 2004

Part 2

Ok, some time has passed since the first tutorial about faking caustics. But this gave me the time to try out some more things, so welcome to faking caustics part 2.

It gives you more control about the look of the caustics and the result (in my opinion) looks really better then the results from the first tutorial.

We start again with a basic scene:

image 1

This sample scene just consists of a ChamferCylinder and a Geosphere on top of a plane, but feel free to use any geometry you like. Of course we have a light in there, too (caustics without light cause some problems, you know? ;) ).

Let's name that light caustic light and cast it white, raytraced shadows with a density of about 5 (we won't see much of our shadows otherwise):

image 2

If we do a quick render now, we end up with:

image 3

All right, white shadows. But there's something more:

We open the material editor and create a standard material with a blue diffuse color (because it'll be the material for our blue cylinder).

Now on to the trick-part: Add a fallof material as the opacity map:

image 4

If we render now, the result looks something like:

image 5

(Note: I already created a second material for the sphere and put some refraction into it, to give it a more glas-like look, but that has nothing to do with the appearance of our caustics.)

Well, something certainly is there but aren't the caustics somehow inside-out? Sure, so let's fix this:

Open the opacity-falloff map and just exchange the front and side materials so it looks like this:

image 6

Render, and tata:

image 7

Better, isn't it? (sure it is, even better than the results from tutorial 1, but hey, why write a second one otherwise?)

But you certainly miss the harsh look that caustics usually have, so on we go to trick number 2.

In the falloff editor go down to the mix curve and add a new point to it:

image 8

Now move the point a little to the upper left:

image 9

If we render again, we nearly got the right look:

image 10

What do we need more? Yap, the rest of the shadow. Because as the amount of light passing the object remains the same, the concentration at the center leads to very dark shadows near the edges.

What we are going to do is clone our caustic light (name it "shadow light" or something) and set the color of the "caustic light" to black:

image 11

Now we take the "shadow light", leave the color and shadow color as is but set the shadow type to "Shadow Map" and the shadow density to -2.0:

image 12

Rendering gives us the final result:

Fake Caustics Tutorial: Final Result

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