A homebrew developer has achieved real-time ray tracing on the 1994 Sega Saturn, demonstrating the console's untapped potential decades after its release.
A recently published video shows real-time raytraced shadows in a game environment running within the improbable confines of a mid-1990s console. The Sega Saturn was notoriously complex and difficult to optimize games for when it was introduced. However, this video shows that there are still surprises being wrung out of Sega's dual-CPU and dual-video-processor system, which debuted in late 1994.
Match that PSX!
Real-time raytracing began to become a mainstream feature of gaming graphics on PCs with the launch of Nvidia's first RTX 20-series graphics cards based on Turing GPUs (late 2018). Some would argue it took another generation and the wide adoption of modern upscaling tech to actually see mainstream raytraced games' momentum. Thus, seeing any kind of real-time raytracing in action on a 1994-vintage console is fascinating.
XL2 introduces their real-time raytracing on the Saturn video clip by saying, "Here is a raytracing test in a small room. The function is pretty simple and could be optimized further: I simply test all the vertices using the BSP [Binary Space Partitioning]." Moreover, it is explained that several other optimizations are in place: the engine only tests the vertices of 3D objects, with only a quarter of them updated per frame, and light sources are kept to a minimum.
The Saturn homebrew dev hints that the demo we see may be improved in due course. They indicate that a number of paths to refinement are available, some of which would be "super easy," while others may need "a bit more maths." So stay tuned to XL2's channel if you like what you see.
Some Sega Saturn history
Sega's Saturn was the iconic game company's first 32-bit console from the ground up, designed to excel at 2D arcade ports, yet still capable of running emerging 3D-centric titles. Launched in Nov 1994 in Japan / May 1995 in the U.S., it would become available at roughly the same time as the original Sony PlayStation (PSX, PS1) in both these key territories. In general, the PSX was weaker at 2D, but offered more balanced, dev-friendly 3D capabilities. Both the Saturn and PSX pre-dated the Nintendo 64, still cartridge-based but a strong 3D performer, by a year to a year and a half.
Sega followed up the Saturn with its awesome Dreamcast, which would be its final console hardware release, giving way to the Sony / Nintendo / Microsoft era.
The achievement is particularly noteworthy given the Saturn's architecture. The console featured two Hitachi SH-2 32-bit RISC processors running at 28.6 MHz, along with dual video processors (VDP1 for sprites and VDP2 for backgrounds and scrolling). This complex architecture, while powerful, made development challenging compared to the more straightforward design of the PlayStation.
What makes this ray tracing demo even more impressive is that it's running on hardware that was designed primarily for 2D graphics performance. The Saturn excelled at 2D games and sprite-based graphics, which was its primary design goal to compete with the SNES and Genesis in the 2D era. The fact that someone has managed to implement real-time ray tracing - a technique that requires significant computational power for ray-object intersection tests and lighting calculations - speaks volumes about both the hidden potential of the hardware and the ingenuity of modern homebrew developers.
The use of BSP (Binary Space Partitioning) for the ray tracing implementation is particularly clever. BSP trees are a data structure that recursively subdivides a space into convex sets by hyperplanes. This technique was actually used in some early 3D games like Doom for rendering optimization, making it a natural fit for the Saturn's architecture and the mathematical capabilities of its processors.
For those interested in the technical details, the homebrew developer's approach of only updating a quarter of the vertices per frame is a form of temporal coherence optimization. By spreading the workload across multiple frames, the system can maintain real-time performance while still providing the visual benefits of ray-traced shadows. This kind of optimization would have been essential on the Saturn, given its limited processing power compared to modern systems.
The light source limitation mentioned is also a practical consideration. Each additional light source in a ray tracing scenario exponentially increases the computational complexity, as rays must be traced from each light source to each visible surface. By keeping light sources to a minimum, the developer ensures the demo remains playable while still demonstrating the core concept.
This achievement joins a long tradition of homebrew developers pushing legacy hardware beyond its original specifications. From demos showing modern graphics techniques on the NES to complex simulations running on the Game Boy, the enthusiast community continues to find new ways to extract performance from classic systems. The Saturn, with its complex architecture and dedicated following, remains a particularly interesting platform for such experimentation.
As the developer suggests, there's potential for further optimization and refinement. Given the rapid pace of development in the homebrew scene and the increasing availability of development tools and documentation for legacy systems, we may see even more impressive demonstrations of the Saturn's capabilities in the future. This could include more complex lighting models, additional light sources, or even integration with other advanced rendering techniques.
The timing of this demonstration is also interesting, coming as it does in an era where ray tracing has become a buzzword in gaming. Seeing this technique implemented on hardware from the mid-1990s provides a fascinating contrast to modern implementations that require dedicated RT cores and significant GPU power. It serves as a reminder that many of the techniques we consider cutting-edge today have roots that go back decades, and that with enough ingenuity, even seemingly limited hardware can be made to perform remarkable feats.
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