Rendering Portals in Virtual Reality

TL;DR

This work addresses the VR-specific challenge of rendering portals to extend space without breaking immersion. It proposes unobtrusive transitions using a portal-box approach and analyzes performance costs with a test scene. The paper demonstrates two optimisations—stencil-buffer masking and single-pass instanced rendering—to reduce the per-portal cost and discusses practical trade-offs. The findings illuminate how portals can be made viable in VR, informing design decisions for immersive, space-extending experiences.

Abstract

Portals have many applications in the field of computer graphics. Recently, they have found use as a way of artificially increasing the available space in a virtual reality (VR) environment. In this paper, we will cover a technique for making the transition through a portal unnoticeable to the user. Additionally, we will measure the performance impact of rendering portals in a test scene and provide some insight into possible optimisations.

Figures (12)

• Figure 1: Four rooms with portals (in red) can all be accessed without leaving the smaller real spacelochner:2021.
• Figure 2: What should the right-eye camera render if it is inside the portal wall (in grey), but the centre of the head (in red) has not crossed the portal plane? If nothing is done, the blue part of the user's field of view would not render the next room, but whatever is inside or behind the portal wall.
• Figure 3: The sides of the portal box are only visible from the side with a solid red line. Therefore, the right eye can see space $B$ on the inner wall and simultaneously look out of the portal box back into space $A$.
• Figure 4: The test scene with no portals enabled.
• Figure 5: The connected blue and green portals are enabled.