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I'm trying to project a caustics texture from a light in Cycles. It works with Point or Spot lights, but I'm trying to emulate the sun projecting caustics underwater, so I need the shadows and light rays to be parallel. Here is an image from the test scene, note that the shadows are not parallel.

enter image description here

And here's the light's material setup:

enter image description here

The question is if there's a way to project from a Sun light. I know that an option is to take the light far, far away (that's why the Light Falloff Node is there, for controlling the strength).

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    $\begingroup$ The Wiki states Their position is not taken into account; they are always located outside of the scene, infinitely far away, and will not result in any distance falloff. which leads me to believe that it would not be possible, as there would be no way to map the texture to a source set up like that. The exact reasons you want to use it makes it an impossibility I am afraid. $\endgroup$ – VRM Feb 2 '15 at 23:49
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Short answer:

No.

Long answer:

Their position is not taken into account; they are always located outside of the scene, infinitely far away, and will not result in any distance falloff.

Which leads me to believe that it would not be possible, as there would be no way to map the texture to a source set up like that. The exact reasons you want to use it makes it an impossibility I am afraid.

Alternative answer:

You can project an image from a plane with a simple Transparent BSDF setup between any light and your subject.

enter image description here enter image description here

And it also works with volumetrics:

enter image description here

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  • $\begingroup$ Yeah I "figured out" already... Anyway, the only alternative is to project the shadow of a texture with Transparent BSDF, and it works with volumetrics too. I think this might improve the answer, I even have a render to illustrate it. $\endgroup$ – Antonio Buch Feb 11 '15 at 11:16
  • $\begingroup$ @AntonioBuch Go ahead and edit my answer, I can clean it up after you add that. $\endgroup$ – VRM Feb 11 '15 at 11:58

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