Over 30 years ago, way back in 1992, developers id Software launched Wolfenstein 3D on PCs. Unbeknownst at the time, it also kick-started an evolutionary tree for a series of game engines that are not just synonymous with id Software's subsequent Doom and Quake franchises, but are also famous for pushing the boundaries of graphics rendering.
Yes, we're talking about id Tech, and with Doom: The Dark Ages, we've now reached version eight. Of course, game engines are more than just about graphics, but it's arguably what made id Tech as famous as it is.
So let's take a journey through each successive version of the evergreen game engine, looking at the first game to use it, what made it stand out from the crowd, and take a quick browse through the work of other developers that licensed id Tech for their own projects.
id Tech 0 | Wolfenstein 3D (1992)
In 1992, id Software's programming duties were handled by just three people: John Carmack (graphics and runtime code), John Romero (tools used to make the game), and Jason Blochowiak (sub-routines). Together, they created what would eventually be called id Tech 0, though at the time, it was simply labelled 'Wolfenstein 3D engine'.
It wasn't the first game that Carmack coded to use 3D graphics, though he chose an unusual method for rendering the three-dimensional world: ray casting. In some ways, ray casting is similar to the ray tracing we see in the very latest games, but due to the limitations of gaming PCs in the 1990s, Carmack was forced to keep it very simple.
In Wolfenstein 3D, the graphics rendering starts with the engine creating the ceiling and floor via a flood fill, as two blocks of colour. Then one ray is cast or 'marched' out for every vertical line of pixels—for a resolution of 1080p, that would be a total of 1920 rays. Of course, in 1992, we're only talking about 320 or so rays!
Each ray traverses a two-dimensional map of the world and travels until it reaches an object, such as a wall or door. From how far the ray has travelled, the object's size is calculated and appropriately scaled, to give the impression of depth. A spot of clever math is also used to correct the perspective of the objects, otherwise, everything would look warped, fisheye lens style.
Once this is all done, the engine then colours and textures the column of pixels, before moving on to the next ray. After all of this has been achieved, objects such as enemies, ammo, and food are rendered in the form of 2D sprites.
We've skipped over a lot of the technical details, but if you're interested in understanding exactly how it all works, then grab a copy of Wolfenstein 3D Game Engine Black Book by Fabien Sanglard.
id Tech 0 would be licensed by a handful of other developers, with the most notable being Apogee Software, which created the Rise of the Triad, a game that we reckon everyone should play at least once.
id Tech 1 | Doom (1993)
For id Software's 1993 follow-up, the seminal Doom, Carmack created an improved rendering algorithm he developed for the SNES version of Wolfenstein 3D. Instead of using ray casting to calculate what should be displayed, Doom's engine (aka id Tech 1) handles all of this through a BSP tree or binary space partitioning tree.
Just like its predecessor, Doom's levels are all 2D maps, and a BSP algorithm is used to split them up into a data structure that makes it super quick to work out if something is visible or not.
Vertical surfaces are rendered first, such as walls and doors, by working through the BSP tree. This is followed by all the horizontal surfaces—ceilings and floors—that don't get rendered during the 'vertical' phase. 2D sprites are handled next, to fill the world with monsters, weapons, and ammo, before the final effect—the game's head-up display.
Just as for Wolfenstein 3D, Fabien Sanglard has written a superb breakdown of the making of Doom and how its engine fundamentally works. If you want to know exactly how BSPs are used in the game, then the Doom Game Engine Black Book is a must-read.
Doom's impact on the world of gaming is hard to overstate—not just in of shaping genres and game design, but also in how its engine would be licensed by other developers to create very successful games. Wolfenstein 3D and Doom's engines would only be used in a handful of other games, though the latter would be used to create the fantastic Heretic and its sequel, Hexen.
But things really changed for id Software's next big release.
id Tech 2 | Quake (1996) | Quake 2 (1997)
Given Doom's rampant success, it was always going to be a challenge to come up with something better. Fortunately, 1996's Quake would turn out to be just as influential as its predecessor. This was in no small part due to the new game engine that Carmack and co created, as id Tech 2 sported an entirely new renderer.
Instead of flat maps drawn to mimic three dimensions, then overlaid with 2D pre-rendered sprites, Quake's engine handled everything in true 3D. Just like most games do today, arrays of vertices were used to generate polygonal meshes, where the engine transforms and lights them, before rasterising them into pixels.
Textures are then applied to each polygon in one rendering , with pre-rendered lightmaps blended in a second .
The result was a world that you could look at and move in any direction, with surfaces no longer constrained to be full vertical or horizontal. Those pre-rendered lightmaps did a great job of giving a sense of realistic lighting and shadowing—for 1996, of course!
1997's Quake 2's engine was more of the same (i.e. still essentially id Tech 2), just with sensible improvements all around, such as using the OpenGL API for rendering, allowing for better graphics and performance on graphics cards that ed it.
But perhaps what made the engine really stand out is the number of other developers who licensed either and used it to create some outstanding games. Half-Life.
ittedly, Valve rewrote an awful lot of id Tech 2 for its masterpiece, as well as created its own tools and additional sub-routines, but if it didn't exist in the first place, would Half-Life have been as good as it was?
id Tech 3 | Quake 3 Arena (1999)
With Doom sidelined in favour of Quake, id Software chose a multiplayer focus for 1999's Quake 3 Arena, but that didn't mean Carmack gave up pushing the graphics envelope to new heights.
Quake 3 Arena's engine (they still weren't being labelled as id Tech at this stage) introduced three big improvements for graphics: spline-based curved surfaces, shaders, and a fast inverse square root function.
The first one solved the problem that 3D polygonal games suffered from at the time: how to make a surface look curved instead of angular. This was done by using Bézier patches to tessellate, or split up, a mesh into dozens more smaller triangles, which together give the impression of a curved surface.
Today's graphics cards can handle billions of triangles, but back then, it was a major breakthrough in producing ever-more realistic graphics at a playable frame rate. That said, Quake 3 Arena could still bring the most powerful of gaming rigs to its knees once the resolution and graphics settings were maxed out.
The shader system used in Quake 3 Arena was very much a precursor to the shaders used in today's games. Rather than just applying a base texture and lightmap to a polygon, the engine used small scripts to describe the properties of a surface. In this file, there would be information about textures, blending, volumes, emissivity, and even what audio files should be played if the player interacts with the surface.
And while he didn't invent the technique itself, Carmack's implementation of calculating the inverse square root of a number—that is, one divided by the square root of something—became famous in programming circles for being a masterpiece in optimisation and speed.
But what truly made id Tech 3 stand out was the sheer number of games created with it, and the list reads like a 'Who's Who?' of gaming. The two Star Trek: Elite Force shooters, two Medal of Honor games, the original Call of Duty, the Star Wars Jedi Knight duo, Soldier of Fortune's sequel, Return to Castle Wolfenstein, and American McGee's Alice, to name but a few!
For its next big release, though, id Software decided it was time to return to an old classic.
id Tech 4 | Doom 3 (2004)
Doom 3 appeared in 2004, and once again, id Software used a new engine, id Tech 4, to raise the graphics bar to a new level. Texturing was now far more advanced, ing the use of normal and specular maps to improve the level of fine detail on surfaces.
To make this even better, though, Doom 3's renderer calculated all of the lighting on a per-pixel basis, rather than just colouring a triangle's corner (a vertex) and then interpolating that across the rest of the polygon.
Doom 3 also used stencil buffers for its shadow volumes, and together with the per-pixel lighting, the game's visuals were second to none. However, the game's performance wasn't so great.
The original Doom was all about frantic, fast-paced action, whereas Doom 3 was considerably slower—almost like an action, survival-horror game. But even so, the use of stencil buffers and the lighting algorithm demanded the very latest GPU features, leaving a lot of older hardware unable to run the game, and even with a high-end graphics card, the performance was never great.
id Tech 4 was less popular with other developers, too, and compared to Quake 3 Arena, only a small number of studios used it for their games. Still, it gave us the much-maligned Brink.
Five years after the launch of Doom 3, id Software was acquired by ZeniMax Media, which also owned Bethesda Softworks, and from that point onwards, id Software's engines would only be used by itself and ZeniMax's other studios.
Doom 3's engine would also be the last one that id Software ever released the source code for.
id Tech 5 | Rage (2011)
In 2011, id Software once again introduced a new engine with a new name, and even a new game IP. Rage was powered by id Tech 5 (the older engines were then retrospectively renamed in the same manner), and its main standout rendering feature was a technology called MegaTexture.
Technically known as virtual texturing (pdf warning), the method involves using incredibly large textures, up to 128,000 pixels square, where sections would be sampled to be applied to a polygon mesh. The idea behind this is that the main, massive texture would stay in system memory and only the parts required would be streamed into the GPU's local memory.
The benefit of this is that id Software could make one renderer that would work exactly the same, regardless of the hardware platform. Unfortunately, the reality was a whole heap of bugs and rendering glitches at launch, though when everything did work well, the texture quality was certainly better than many other PC games at that time.
It helped that id Tech 5 was packing a whole raft of other graphics tricks, such as soft shadows, HDR rendering, volumetric lighting, screen space reflections, depth of field, and motion blur. ZeniMax Media had two of its developers use id Tech 5.
MachineGames created the Wolfenstein reboots of The Evil Within series, albeit heavily rewriting id Tech 5 for the second title.
In 2013, John Carmack left id Software for new ventures, the last of the original team to leave, ing Oculus VR to help develop its virtual reality hardware and software.
id Tech 6 | Doom (2016)
It was a bold move to reboot such a well-known franchise, but that's exactly what id Software did, and in 2016, Doom returned and with one hell of an engine.
While he was still at id Software, John Carmack explored the use of ray tracing and voxels for the next id Tech iteration, but when he left, the developers stuck to a traditional polygonal mesh renderer with standard rasterisation to create id Tech 6.
MegaTextures were still in full use but higher in quality, and along with the entire dictionary of modern rendering techniques, the new Doom not only looked extremely good, but it ran very well, too.
It also had a couple of new tricks up its sleeve, such as temporal anti-aliasing, or TAA. This had already been around for a while, but id Tech 6 added the use of super-sampling of motion data to remove the shimmering and blurring that TAA is well-known for.
While it might sound like id Tech 6 didn't bring anything significant to the world of rendering, Adrian Courrèges' breakdown of the graphics in Doom (2016) shows just how complex and multifaceted everything is behind the scenes.
Sadly, id Tech 6 would only be used two more times, by MachineGames again, for two more Wolfenstein games —RTX technology, though, as it was an early implementation of ray tracing, the results didn't justify the performance hit.
id Tech 7 | Doom Eternal (2020)
For 2020's Doom Eternal, id Software took id Tech 6 and gave it a thorough overhaul, removing the OpenGL code in favour of Vulkan-only, as well as dropping MegaTextures.
By now, id Tech was running as a heavily multi-threaded engine, and instead of using a primary thread to handle the rendering, multiple threads were tasked to operate in parallel, handling shaders, asset streaming (geometry and textures), and data decompression.
The end result is a game that has vastly more detail than its predecessor and even more accurate lighting and shadows, and countless more particles for explosions and gore. And remarkably, it runs even faster than id Tech 6.
A year after launch, Doom Eternal was updated to Nvidia's DLSS AI-powered upscaler and frame generation technologies, along with ray-traced reflections, to allow all surfaces to reflect the environment correctly.
Ray tracing would be used exclusively for lighting and shadowing in the only other game to use id Tech 7, Indiana Jones and The Great Circle—MachineGames, once again—and this almost certainly laid the foundation for the next iteration of id Tech.
id Tech 8 | Doom: The Dark Ages (2025)
And so we come to Doom: The Dark Ages and its id Tech 8 engine—a prequel to the 2016 Doom game but with all the graphical enhancements that MachineGames' Indiana Jones offered.
With ray tracing used all the time, and with no shader-based fallback system for GPUs without ray tracing hardware, id Tech 8 was never going to be as speedy as its predecessor, but it still runs pretty well, all things considered.
We're still learning more about what id Tech 8 has underneath the hood, as id Software has been pretty quiet about its new engine, but we do know that Doom: The Dark Ages will be patched in the near future to path tracing.
This is a method of ray tracing that produces the most physically accurate lighting, shadows, reflections, and refractions, but as any PC gamer who's tried will tell you, the hardware demands are incredibly high.
Naturally, it will mean that upscaling—and perhaps even frame generation—will be an absolute must, and it also means that id Software will need to ensure id Tech 8's denoiser algorithm is top-notch, too.
The slower pace of Doom: The Dark Ages compared to Doom 2016 and Doom Eternal means that the outright frame rate won't be quite as important as it is in those games, but given id Software's track record of developing extremely performant engines of late, we're pretty confident that path tracing will be worth enabling.
Assuming you have the PC hardware for it, of course!
What's next for id Tech?
With a gap of four to five years between each release of a new id Tech engine, we're obviously not going to see another one until the end of this decade. That's sufficient time to allow for two more generations of new GPUs, and if you compare today's graphics processors to those from 2020, we can maybe judge what id Tech 9 will bring to the table.
AMD and Nvidia's latest chips directly use AI to improve performance and image quality, through upscaling, frame generation, and denoising, but the latter also introduced the concept of neural rendering with the launch of its RTX 50 series.
Five years ago, AMD launched its first ray-tracing capable GPUs—the Radeon RX 6000 series—and Nvidia released its second generation of RTX chips, the 30 series. Back then, there was no frame generation, no AI-based denoising. Neural rendering was still in its infancy of research.
This suggests that by 2030, id Tech 9 could be making use of AI to improve the quality of its graphics, to make them ever more realistic, all while keeping the performance as high as possible. The next Doom or Quake game could be permanently path-traced, perhaps always uscaling, too.
But whatever we do get, id Software's long history of creating graphically-intensive games means that we can be sure that we'll be in for a visual treat.
Although the id Tech engine is no longer the one to watch for new rendering technologies—everything in Doom: The Dark Ages has been done before—it still sets the bar when it comes to optimised performance.
Now, how many game engines can you say that about?
You must confirm your public display name before commenting
Please and then again, you will then be prompted to enter your display name.
