Raytracing made easy: finally guinea pigs again, thanks to Portal RTX and RTX Remix

Even if Nvidia is currently the subject of controversy over the pricing of the cards in its new RTX 40 series – and AMD’s answer to this should be interesting – one should not forget that the graphics card manufacturer presented some very interesting technologies parallel to the announcement of the next GPU generation . In addition to the new cards, there was talk of DLSS 3, for example. But almost more exciting was RTX Remix, a technology that allows modders and developers to quickly add RTX effects and more to old games.

Portal with RTX should serve as a flagship title for this, which visually impressively brings the legendary puzzler into modern times. To find out more about it, I sent a few questions to Nvidia Lightspeed Studios, which was responsible for the implementation of the classic and the development of the tool that should finally make ray tracing more visible across the board.

So below you can read more about the reasons why Portal was chosen, what RTX Remix actually is, how it simplifies the work of developers and what the challenges are when trying to work with the software.

Eurogamer: Portal is a game for the ages and I think it’s held up pretty well visually. Still, what made it a good candidate for the RTX treatment?

NVIDIA Lightspeed Studios: When Lightspeed Studios selects a project, we first consider what excites us the most. As you said Portal is a popular classic, we have a great relationship with Valve and we’ve always wanted to see what ray tracing looks like when light photons flow through portals! For us, ray tracing isn’t just about making the scene realistic – in a game like Portal, which is known for using dynamic elements to enhance the visual experience, we can use ray tracing to amplify the spectacle. Reflections thrown through portals and from every surface make the game so much more interesting.

With the RTX treatment, we’ve worked closely with Valve to ensure we respect the original game’s vision. As an aside, at Valve’s suggestion, we incorporated visuals from Portal 2 to give the Aperture Science Enrichment Center a modern look that works well with the ray-traced lighting. I can’t wait for players to be able to revisit areas they’ve seen many times before with new, stunning details.

Eurogamer: Nowadays, many studios rework and re-release their old games, devoting significant resources to remastering or remaking. Portal RTX was built using NVIDIA Omniverse and RTX Remix. How long did it take you to implement it?

NVIDIA Lightspeed Studios: It’s difficult to judge because we developed RTX Remix alongside Portal with RTX and both served to make the other better and more functional. In total, it took us about a year to complete RTX Remix and Portal with RTX, and with each month that goes by, RTX Remix continues to evolve in its capabilities, making our iteration of Portal with RTX even faster.

Eurogamer: How compatible is RTX Remix with all the different engines and graphics pipelines out there?

NVIDIA Lightspeed Studios: RTX Remix compatibility isn’t fully settled yet, but for now the games need to support DirectX 8 and 9 and have a solid feature pipeline to be compatible. As we get closer to the RTX Remix beta, we’ve fixed more bugs, which has broadly improved compatibility. This is an ongoing focus for us to ensure the library of compatible titles will be extensive when RTX Remix comes out.

Eurogamer: Tell me how it works exactly when you use RTX Remix. How exactly will this make life easier for developers?

NVIDIA Lightspeed Studios: For modding and development, it makes life a lot easier. For Quake II RTX, it initially took our development team 3 months to transition the game from a 32-bit process/X86 instruction set to a 64-bit process/X64 instruction set. This conversion allowed Quake II RTX to be path traced lit and leverage over 3GB of ram for high-quality, physics-based textures. In RTX Remix, these conversions are done automatically, saving valuable time. Although we could have used Valve’s source code for the assets, we chose to do this project entirely with RTX Remix to ensure our modding platform lived up to our high expectations. We used AI texture tools to quickly add physics-based properties to each decal – now the spray paint and blood spatter on walls and glass properly interact with light and differentiate from each other.

Switching to a ray-traced lighting model had its own benefits. If this were a scene-by-scene remake with “baked-in” lighting, we’d have to meticulously ensure that every pixel is lit identically to the old game. But with RTX Remix we can set up a conversion model that converts the old lights into area lights that cast realistic shadows when path tracing. From then on, we worked in a simulation environment – the light behaved like it would in the real world, so we could easily adjust core properties like intensity, color and spacing of the lights to create an immersive scene in an intuitive way. We even added lights to objects (like the weighted cube) to give the player fun RTX toys to play with. We also relied heavily on the Remix application’s extensive debugging tools to ensure the game was technically sound.

One final note: one of the perks of reimagining a classic with RTX Remix is ​​that you can keep the original gameplay feel, as the RTX renderer just changes the way things are rendered. Finally, Portal’s gameplay is timeless and we have no intention of changing it.

Eurogamer: So the degree of automation is quite high. What things still need to be done the old-fashioned way?

NVIDIA Lightspeed Studios: It’s a big part of what we love about RTX Remix – even the manual workflows become significantly easier. In the case of Portal with RTX and Morrowind RTX, we used Omniverse-connected applications like Blender, Autodesk Maya, Adobe Substance and Photoshop, as well as Pixologic ZBrush to meticulously recreate most of the assets. Our artist team updated the elements using the various applications, while our lead artist Vern placed each element in the scene using the RTX Remix application. Because the changes were directly synced, Vern was able to ensure that the objects looked good when illuminated by the Path Tracer and were positioned harmoniously with the rest of the props in the scene. When an object was replaced, every instance of that object automatically changed throughout the game. This combination of automated and manual workflow made it easy for NVIDIA to meet its high visual quality standards—and those of Valve.

Vern also took great care in creating new lights and re-inspecting the locations to place the light sources in a way that felt “RTX” while still maintaining the look of the original. A clever thing our team was able to do with Remix: we attached a light to a moving mesh so the high-energy spheres glow realistically. Using portals to deviate from their designated path and light up the test chambers in unexpected ways is a lot of fun.

Eurogamer.de: What challenges are there when using this technology? Where do developers need to change their processes or their mindset to get the most value out of it?

NVIDIA Lightspeed Studios: The biggest change is that the renderer is independent of the engine that calculates all objects, physics, layers and sound – this requires a rethink of the order of operations. RTX Remix is ​​compatible with other mods partly because of this independence – when capturing, the application does not really notice whether the source is a game or a modded game. It just sees layers, geometry, textures, lights and cameras and goes to work replacing those things. For developers and modders, this means that remastering heavily modified content (e.g. custom levels) must first capture the heavily modified game. Everything is easy and possible, but it requires a new workflow that will feel different for some people.