Originating from the game Portal, portals are pairs of blue & orange holes which can be used to create non-Euclidean environments by linking locations over a distance via an impossibly shallow doorway. This project tries to re-create their visual effect utilising Geometry Shaders, as opposed to using the Stencil Buffer or Render Textures, which other approaches have used previously. In the end, three distinct renderer implementations are used – A single-pass forward renderer, a multi-pass forward renderer, and a deferred shading-inspired renderer utilising sub-passes for each level of recursion.

Through testing of frame intervals, it is discovered that the accuracy of each renderer’s portal effect improves through each iteration, however there is generally a performance penalty with each improvement. Breaking this trend however, the final renderer sees scene dependent improvements to its performance, alternating between the desktop and laptop platforms, creating an unusual profile.