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Eevee: Impossible Area Lamp Reflection
Closed, InvalidPublic

Description

System Information
Operating system: Windows 10 64 bit
Graphics card: Nvidia GTX 750 Ti

Blender Version
Broken: (2.80.0-git.d2d84132ddf9-windows64)

Short description of error
Under some circumstances, the outline (not the full lamp) of an area lamp can be seen in a reflection, where it wouldn't be physically be possible for light to be reflected in that direction.
And even if the light were to be reflected to the area lamp, it should show up as a rectangle, not the outline of one.

Exact steps for others to reproduce the error


  • Press F12 to render or set the left panel to rendered mode.
  • You can see a white outline of the area lamp. I'd expect to see just black.

The scene consists of a camera looking at a cube with a sharp glossy material.
An area lamp is on the opposite side.
The camera shouldn't be able to see the area lamp, even with disabled shadows. (And especially not the outline of one.)

The lamp has shadows disabled (but it can also happen with shadows enabled, I think the problem is unrelated to shadows). Screen space reflections, etc are disabled.

Details

Type
Bug

Event Timeline

Sebastian Parborg (zeddb) lowered the priority of this task from Needs Triage by Developer to Confirmed, Medium.

This is a limitation of the Algorithm. Unreal and Unity (who use the same algorithm) also have this problem.

https://blenderartists.org/t/unreal-rect-light-vs-eevee-area-light/1151377

Increasing shadowing precision can help prevent this.

@Clément Foucault (fclem) Could you please take a look at this: D4662
I believe that this is an easy to fix artifact, by simply checking whether the normal is facing away from the light source (which is when these artifacts occur).

@Philip Holzmann (Foaly) The issue is that this prevents lights from wrapping correctly. It's also not correct for sphere / disk lights.