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I'm using blender 2.76 rc1 with an AMD Raedon HD 7900 series, I'd like to create a volumetric spot light with cycles render. I set the volume scatter (density 0.1) in volume and mist pass in world, and put the spot light slightly below the street light, but, there isn't a volumetric effect.

UPDATE 1: I tried to set volumetric light in a pc with an Nvidia graphic card and works, I think it's an incompatibility problem

UPDATE 2: I read the wiki blender of openCL status, and talks about the AMD limitations, including the volume:

AMD

Limitations

Initial split kernel patch was done by AMD and was aimed to make Cycles render on Windows platform. This kernel works reasonably well with simple scenes, but has much harder time to work on a production files, it also lacks following features:

  • Transparent shadows (they're disabled due to AMD compiler issues)

  • Correlated multi jitter pattern, SSS and Volumes, which could be added to the split kernel, but prefer to focus on making existing feature set rock-solid first.

  • Branched path tracing which is quite tricky to integrate into current implementation of split kernel and supporting it will mean we'll do split kernel once again

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Rendered World Setting

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For volumetric lights you need to control a few things:

The emission values of the lamps need to be a bit higher than normal to compensate for loss due to the volume Scatter.

enter image description here

Rendering will be slower, a lot noisier, and with lots of Fireflies, so be ready to bring up the samples and clamp indirect samples. The best solution time/quality I've found is using branched Path Tracing and increasing the volume samples and a value for clamp indirect around 3.00

enter image description here

Work with the lowest volume scatter value that still yields the desired result. Higher values will be even noisier and the lights will need to be even brighter.

enter image description here

Keep in mind that volumetric light effects are better seen when the background is dark. How you combine your mist pass will make a huge difference as mist will tend to make things brighter and make volumetric lights less visible.

enter image description here

In my opinion a more realistic approach would be not to use mist, but to use volume scatter and volume absortion together.

enter image description here

sample file to play with:

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  • $\begingroup$ The sampling tab gives me only those options -> imgur.com/bH78sI8 $\endgroup$ – user18210 Sep 19 '15 at 18:18
  • $\begingroup$ I'm using blender 2.7 rc1 $\endgroup$ – user18210 Sep 19 '15 at 18:51
  • $\begingroup$ i noticed that the branched tracing path is enabled only when i disable the compute device. I use an amd raedon hd 7980 $\endgroup$ – user18210 Sep 19 '15 at 18:59
  • $\begingroup$ wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.76/Cycles newer versions of blender have better support for AMD cards $\endgroup$ – cegaton Sep 19 '15 at 19:01
  • $\begingroup$ i installed the daily build version, but isn't unlocked; it's possbile without the branched path tracing to see the volumetric light? $\endgroup$ – user18210 Sep 19 '15 at 19:17

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