Quake 2 real-time path tracing using RTX

Still from Q2VKPT - Quake 2 real-time path tracing using RTX taken on 19/01/17

Q2VKPT is the first playable game that is entirely raytraced and efficiently simulates fully dynamic lighting in real-time, with the same modern techniques as used in the movie industry. The recent release of GPUs with raytracing capabilities has opened up entirely new possibilities for the future of game graphics, yet making good use of raytracing is non-trivial. Q2VKPT is the first project to implement an efficient unified solution for all types of light transport: direct, scattered, and reflected light.

Path tracing is an elegant algorithm that can simulate many of the complex ways that light travels and scatters in virtual scenes. Its physically-based simulation of light allows highly realistic rendering. Path tracing uses Raytracing in order to determine the visibility in-between scattering events. However, Raytracing is merely a primitive operation that can be used for many things. Therefore, Raytracing alone does not automatically produce realistic images. Light transport algorithms like Path tracing can be used for that. However, while elegant and very powerful, naive path tracing is very costly and takes a long time to produce stable images. This project uses a smart adaptive filter that re-uses as much information as possible across many frames and pixels in order to produce robust and stable images.

Q2VKPT is implemented in the Vulkan API to be able to use the new hardware-accelerated raytracing features that were made available earlier this year. Thanks to these, the game can actually come close to 60 FPS (2560×1440, RTX2080Ti), while being fully raytraced and dynamically shaded with realistic global lighting models in real-time. Using path tracing for fully dynamic lighting allows for a lot more detail in the shading of game scenes, naturally producing complex interplay of hard and soft shadows, glossy material appearances and perspectively correct reflections everywhere. Moreover, light can naturally flow anywhere, tying the scene together in the ways we would expect from the real world. Traditional approaches like precomputed lighting or coarse real-time raster approximations could never interactively reach this detail at a comparable resolution, since full storage of this lighting information would exceed any memory bounds.

This project is meant to serve as a proof-of-concept for computer graphics research and the game industry alike, and to give enthusiasts a glimpse into the potential future of game graphics. Besides the use of hardware-accelerated raytracing, Q2VKPT mainly gains its efficiency from an adaptive image filtering technique that intelligently tracks changes in the scene illumination to re-use as much information as possible from previous computations.

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