Is it possible to use mist in a Cycles scene in addition to a world background?
First, set a world background.
Then, go to the Render context in Properties and enable
Transparent (in the
Create two render layers. For the first one, enable
Mist (in the
Passes panel). For the second render layer, disable
Z, and enable
Environment. Also, under
Exclude, select all layers (we only want the background texture).
Create this node setup:
The value in the
Multiply node controls the strength of the mist. The result is:
(my settings in the Mist Pass panel of World context were
A very simple way to do it, especially if you don't want to set up a world background or use world geometry, is to use a simple plane with an image texture at the back of your scene and a color ramp for the mist effect in compositing. If the last color of your ramp is black, then the mist won't apply at the background.