Visleaf

A sample scene with two rooms.

The default visleaf structure for the above scene. Note how leaf 2 cannot see leaf 3.

Each visleaf (sometimes referred to simply as a leaf) is a hollow volume in a map which defines a 'cluster' of visible surfaces. Every visible surface of a map is part of one visleaf or another. Visleafs are used primarily by the Rendering Engine to determine (before rendering each frame) which areas of the map might need to be rendered on screen. When any part of a visleaf is potentially visible from any part of the current visleaf, the entire contents of that visleaf are considered for rendering.

Visleafs are generated automatically from the BSP tree by the VVIS compile tool. Each (internal) surface of a visleaf is either a World brush surface or a Portal to an adjacent visleaf.

Examination

Using the Developer Console, mat_leafvis 1 draws a red wireframe box around the Player's current visleaf, which is redrawn each time a new visleaf is entered.

• With Orange Box and later games, you can access Hammer's Map > Load Portal File feature. (Leaf edges that touch other edges will be displayed as thick blue lines.)
• Visleaves can also be examined from the desktop with the glview tool.

See also

• PVS (Potentially Visible Set): the 'cluster' of visleaves that are currently being drawn
• PAS (Potentially Audible Set): as above, but for sound
• Visibility optimization
  • Leaks are gaps in the BSP geometry that prevent leaf generation
  • Hint brushes tell the compiler to split leaves
• Visleaf generation:
  • VVIS compiler.
  • Ralph van Hoorn's excellent explanation of visleafs.