func_detail

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func_detail is an internal brush entity available in all Source games. It creates a brush that does not affect visibility or cause other brushes to be chopped. All brushwork that does not form the 'backbone' of the world (and that is not tied to a real entity) should be detail.

Valve provides an example map at sourcesdk_content\hl2\mapsrc\sdk_func_detail.vmf. You can also load up the HL2 map sources and hide detail brushes with their auto visgroup to see where Valve used them.

Tip:Alternatively, use the console command r_drawfuncdetail to hide detail brushes in any map while it is running.

Effects

The point of creating a detail brush entity is to avoid creating an unnecessary number of visleaves for a mere detail of the map, hence the name of the entity. VBSP will allow visleaves to overlay details, and thus minimize visleaves and compile time.

World-vs-detail.png

Above are a world brush (left cylinder) and a detail brush (right cylinder). The blue lines are visleaf boundaries. The world brush has chopped the map into nine oddly-shaped segments, leading to longer compile times and marginally lower performance, while the detail brush has not changed anything.

Caveats

  • Detail brushes cannot be used to seal a map, or areaportal areas.
  • Because detail brushes do not chop world brushes, light can seep underneath them if the other surface's lightmap scale is larger than the detail brush is wide/tall. If you encounter this, manually slice the underlying brush in two (with Shift+X).
    • This effect can cause detail brushes with lots of surface contact to become inefficient, because the surface beneath them is being rendered too!
    • Detail brushes do chop each other, however.
  • Surfaces on very thin (about 2 units thick) detail brushes have been known to disappear at certain distances. As a workaround, use func_brush instead.
  • World brushes with translucent materials applied, or which are displacements, will be treated as detail, and cannot seal areas.
    • World brushes w/ translucent material will still chop leaves, but to no effect.
  • Detail brushes will, in some cases, merge faces with other detail brushes, and on occasion, world brushes, which can cause them to create leaves.
  • Under normal conditions, any time a detail brush contacts a world brush, VBSP will note the junction and optimize it. This connection is known alternately as a T-junction and a water index, and there is a limit to the number of T-Junctions VBSP will attempt to fix (65,535). Excessive use of detail brushes in contact with world geometry could cause VBSP to abort compilation with an error. Using the -notjunc option will skip this optimization at the price of possible visual inconsistencies.

Good candidates

There's not much left of City 17 Trainstation Plaza once we remove detail brushes. Valve has missed a few world brushes as well...

Any brush which doesn't significantly block the player's view should probably be detail. Specific examples include:

  • Pillars, plinths and supports
  • Free-standing walls
  • Suspended walkways
  • Steps (create a smooth wedge-shaped world brush underneath)
  • Small buildings
  • Rotated brushes
  • Very small or thin brushes
  • Brushes in the 3D skybox. (Excluding displacements)

Keyvalues

DXLevelChoice:

Minimum DX Level <choices>
Maximum DX Level <choices>
The entity will not exist if the engine is running outside the given range of DirectX Versions. Don't use this with anything that will break saved games should a player switch dxlevel!
  • Default (no bounding)
  • DX7
  • DX8
  • DX8.1
  • DX9 SM2
  • DX9 SM3

See also