Context. A portal in computer graphics is an opening which connects two spaces together. Portals can be used for occlusion culling for indoor environments or wormhole-like effects. This thesis address the latter and focus on how objects interact with such portals.

Objectives. The objectives are to provide a solution to how objects can interact with complex portals in real-time with focus on visual (and physical) correctness and also present a background to how simple and complex portals work.

Methods. A hybrid approach of a geometry and image technique is used to render portals. Intersection techniques and a technique related to constructive solid geometry is used to solve object-portal interactions. The research methodology used is implementation and simple analysis of the results is performed.

Results. The results show that the implementation of the object-portal interaction scales exponentially. In the worst case it has a complexity of O(n² * m²) where n and m are the number of triangles in the object and portal respectively. Increasing the number of triangles in the object shape is more costly than increasing the number of triangles in the portal shape by the same amount. The results were not compared to previous knowledge as no results have been published of other object-portal interaction methods. The rendering of portals scales linearly with the number of triangles used to represent it.

Conclusions. This thesis extends the state-of-the-art portal rendering system and adds a solution to object-portal interaction of complex shapes. It also provides a detailed background into the fundamentals of portals and their nature. The thesis is of interest to those who want object-portal interaction of both simple and complex portals used in gameplay and special effects without restriction on portal placement and shape, with the exception that portals may not have holes in their shape in the direction an intersecting object is moving.