Define Foreground objects

All objects defined as “Set as foreground actor” which are equal to the “Foreground Objects” list within the Shield Actor, are part of the seperated foreground render pass.

The foreground renderer is a completly seperated render pass which supports everything like the normal background renderer.
An alpha channel will be generated automatically.
Simply set the SDI output to Key&Fill to get seperate access to the RGB and to the Alpha pass.

The mesh actor is defined as foreground object (screenshot in edit mode/not in play)

The mesh actor will be rendered seperatly within the same lighting environment, but without “Atmosphere objects”

Atmosphere in Foreground behaviour

By default all “Atmosphere objects” will be not rendered within the Foreground pass, this includes:

  • Volumetric Clouds
  • Sky Atmosphere
  • Exponential Height Fog
  • Atmospheric Fog

Typically, these “Atmospheric Objects” doen´t generate an alpha channel and can have “issues” by using external compositor or the internal composeting, by using additive blend modes.

Foreground with enabled “Atmosphere” settings

“Atmosphere Objects” don´t have an alpha channel

Reflection from Background into the Foreground

Planar Reflection for the foreground objects can be used to effect reflection from the background into the foreground objects.

Shadow from Background into the Foreground

“Static” and “Stationary” backgrounds objects effects automaticly Foreground objects.

Only the “preview mesh” is defined as foreground object.

The cube is rendered in Background but effects the foreground objects with shadow.

“Simple mode” enabled. So the cube will not effected the foreground object.

Alpha Stencil

By default all “Post Processes” within Unreal like “Bloom”, “Lens Flares”, etc. dosn´t have a alpha channels.
In some cases if the external compositing hardware dosn´t support “premultiply alpha” and only add the RGB channels which have an valid alpha channel the “Post effects” will not added correctly.

Foreground object with a lot “Bloom” and “Lens Flares”

By default Unreal only creates a alpha stencil from the mesh

Alpha channel if “Alpha Stencil” is deactivated