ZP+: Correct Z-pass stencil shadows

Samuel Hornus, Jared Hoberock, Sylvain Lefebvre, John Hart

Research output: Contribution to conferencePaperpeer-review


We present a novel algorithm for the rendering of hard shadows cast by a point light source. The well-known Z-pass method for rasterizing shadow volumes is not always correct. Our algorithm, which we call ZP+, elegantly corrects Z-pass defects. ZP+ takes advantage of triangle strips and the fast culling capabilities of graphics hardware not available to conventional robust methods like Z-fail. While Z-fail can be up to 80% slower than Z-pass, our new method ZP+ is typically less than 10% slower than Z-pass. Finally, we compare the three methods. When a scene is geometry-bound, ZP+ is always faster than Z-fail. We also explain why, in some situations, Z-pass (hence ZP+) is surprisingly slower than Z-fail on more recent graphics hardware.

Original languageEnglish (US)
Number of pages8
StatePublished - 2005
EventI3D 2005: ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games - Washington, DC, United States
Duration: Apr 3 2005Apr 6 2005


OtherI3D 2005: ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games
Country/TerritoryUnited States
CityWashington, DC


  • Graphics hardware
  • Real-time rendering
  • Shadow volume
  • Stencil shadows

ASJC Scopus subject areas

  • Software
  • Human-Computer Interaction
  • Computer Graphics and Computer-Aided Design


Dive into the research topics of 'ZP+: Correct Z-pass stencil shadows'. Together they form a unique fingerprint.

Cite this