I am trying to render a scene with volumetric spotlights and am using HDRI (mapped as a world texture) for reflections in a shiny metal object in the scene.
The scene has the reflective object with the volumetric light directly behind this object so that the rays, but not the light are visible to the camera.
In order to see the volumetric light effect I seem to need have an object (in this case a large, shadeless black plane - this gives the effect that the light is shining out of the dark like a streetlamp in the fog) behind the rays of volumetric light - the light doesn’t seem to show up when it is just empty space behind. The problem with this is that the plane then gets reflected in a shiny metal object, it blocks the HDRI reflection on the edges of the object.
Hopefully this makes sense, is there any other way this could be done? Is there another way to map the hdri scene reflections onto the texture of the object without it being mapped to the world, and without it showing in the background of the scene?
Easy way or hard way I don’t care. Can I provide any better information to help with this?
Volumetric lights are simply not seen against the background in yafray, because the light functions creating the effect don’t get called at all when nothing is hit.
This can only be solved by a separate volumetric handler, but that has to wait until the new core design is done…
You can render your image in Yafray without the halo lights and then bring the image back into Blender’s node editor to composite your halos back into the image. Depending on how your scene is set up, you may have to use the alpha channel of your Yafray image to mask off any portions of the volumetric lamps that might be hidden from the camera’s view by various scene geometry. This is done via “Color” nodes ( space bar>add>color>“mix”, “alpha over”, etc…There are several ways to go about it. Try using a subtract node to use the alpha channel from your Yafray image or even from a renderlayer node to knock out any areas of volumetric light that arent rendering where they’re supposed to. If you’re not familiar with the nodes then all this probably sounds like “yakity, smakity, blah, blah, blah…” If you need to ,pm me and I’ll send you a Blend file with an example of how it’s done.
Kernond, yes the halo is on, and that link was doing something similar but without the complication of HDRI.
Lynx3D, is a new volumetric handler in the wings? Or are you suggesting it would never work without a “theoretical” core redesign.
Rambobaby, thanks, I am not so good with the nodes yet, but have achieved something similar by just rendering various scenes with alpha and combining in the gimp. Hopefully I can show the end result when I am finished it.