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The Build Process

In the unreal engine, as in most 3d game engines, you can't play the game straight after adding the last piece of architecture and a player start. You need to build it, also known as compiling it. This process can take anywhere from a few seconds to an hour (based on year 2002 PC performance).

This automatic process consists of several stages:

  1. Applying structural brushes
  2. Zoning
  3. Illumination occluding
  4. adding detail brushes
  5. Building polygons
  6. Merging planars
  7. Partitioning
  8. Zoning
  9. Illumination occluding
  10. Optimizing Geometry
  11. Allocating Meshes
  12. Computing Visibility
  13. Raytracing
  14. Adding reachSpecs

Start the Rebuild

To launch the process you have a row of dedicated icons in the Toolbar.

Legacy interface.toolbar.png
  • 14 The cube only rebuilds the geometry. No lights are computed and any existing lighting is removed (steps 1 - 7).
  • 15 The light bulb icon only calculates the texture illumination (when applying new brushes or rescaling textures on brushes) (steps 12-13).
  • 16 Launches the navigation Array rebuild (steps 14 -15).
  • 17 The icon with a cube and a light bulb builds according to the options held in the Build Window.
  • 18 The last icon, horizontal sliders, opens the Build Window itself.

Build options


Setting Advantage Disadvantage
Lame quick build times can create unnecessary polys
Good decent build times, pretty accurate not accurate enough for final build
Optimal automatically merges polys longest build time

Understanding the Slider

The slider bar allows the map builder to optimize the map for speed. It makes adjustments to the number of BSP cuts which affects performance and frame. Few maps are perfectly open or highly occluding, so the number of cuts must be determined per map.


  • creates a sparse BSP tree
  • quick to lookup the BSP tree which renders the scene
  • best on open areas where little occlusion occurs
  • disadvntage: may need to lookup more in the BSP tree when occluding areas are encountered


  • dense BSP tree
  • the BSP tree knows which items are drawn in front of the other ahead of time
  • Best used when many occluding surfaces
  • disadvantage: can overdraw areas when in non-occluding or open areas

The default of 15 cuts has been found best for most maps.

Other stuff

  • Rebuild on visible actors option is extremely useful. Needs a mention here & link to Hiding Actors
  • Talk about errors and solutions when reviewing the logfile on a build

Technical stuff

"adding detail brush" refers to the semisolid brushes. Evidence for this: the number of detail brushes is equal to the number of semisolids.


  • The structural brushes count goes up to 359 / 512.
  • Number of semisolids in the map (use MAP SELECT SEMISOLIDS) = 153

Related Topics