Though firmly rooted in the Microsoft technology camp for much of their history, in the past few years Valve has been expanding their reach to additional platforms and technologies. This started with porting their own games to OpenGL based OSes – first Mac OS X and later Linux – and of course more recently their efforts in rolling their own Linux distro with SteamOS. Throughout all of these processes Valve has been relatively open about what they’re doing and how they’re doing it, and this week they’re getting a bit more open on the API side.

Posted this week to GitHub, Valve has released the source code behind their “ToGL” shim to the public. ToGL is the translation layer Valve uses to bring OpenGL support to their games, essentially emulating a limited subset of the Direct3D 9.0c API and translating those calls to OpenGL. It is implemented within the game binary itself (this isn't an external wrapper), so this is primarily a tool for game developers. And although not particularly common, translation layers such as ToGL and even bigger full-on wrappers are often used to bring big budget multiplatform games to OpenGL platforms, as the PC ports of many games are still primarily coded against Direct3D and native OpenGL renders are sparse.

This release of ToGL comes from Valve’s latest game, DOTA2, with Valve pulling ToGL directly from said game’s source tree. Valve’s release notes, though short, give us a quick idea of just how large of a subset of Direct3D 9.0c ToGL supports. Since it’s not a full Direct3D 9.0c implementation, only part of Shader Model 3 is offered; multiple render targets (which are heavily used these days) are supported, while vertex texture fetch is not. Meanwhile we can see that Valve has been doing shader translation (HLSL-to-GLSL) at a bytecode level, rather than doing the translation at a higher level.

Finally, though Valve’s notes don’t specifically state why they’re releasing ToGL to the public at this time, it’s readily apparent from their releasing it in open source form and their choice of license that they’re looking to spur further Mac OS X and Linux ports of games. By opening up ToGL to other developers and making it free to use via a BSD-style license, developers building games targeting Direct3D 9.0c have an avenue for making the porting of the graphics layer significantly easier.

Though with that in mind, it remains to be seen just how productive it will be to release a Direct3D 9 shim at this point in time. With Windows XP’s retirement next month, all supported versions of Windows will support Direct3D 11 (feature levels not withstanding), so the number of games being written against Direct3D 9 will be low. On the other hand this would still greatly speed the porting of older games, which could help to further build up the list of games available on SteamOS.

Source: Github (via GamingOnLinux)

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  • edzieba - Tuesday, March 11, 2014 - link

    "they seem to be all about resisting change and legacy technology"
    Apart from all that, you know, VR research and the like.
  • skiboysteve - Tuesday, March 11, 2014 - link

    Good point. Maybe I should say their PC technology is stuck in 2000s, and they seem to like it that way. They are definitely looking outside of PC technology though
  • inighthawki - Tuesday, March 11, 2014 - link

    Surprise, it's what I've been telling people for months. This is a port of DX9, meaning their old "OpenGL is faster than DX" statement is at best wildly inaccurate. They use a 10 year old API for their comparison which has more overhead than DX11. Congrats to Valve on providing misleading perf statistics.

    Now Valve, how about comparing a native OpenGL port to DX11 so we can actually see the difference? It's not hard to rewrite an API on top of modern techniques and hardware to be faster than some old legacy pipeline.
  • blzd - Tuesday, March 11, 2014 - link

    Last I checked 99% of games still ran DirectX 9. DX11 support usually consists of 1 or 2 extra options, some type of bonus depth of field and tessellation.
  • Friendly0Fire - Tuesday, March 11, 2014 - link

    It's changing very rapidly now that the new consoles are around. Prior to that, every multiplatform game basically required DirectX 9 anyway, since that's what the Xbox 360 supported (it's not exactly DX9, but close enough).

    Already, the new versions of CryEngine and Unreal are DX11 and DX9 versions are at best legacy, at worst entirely unavailable.
  • inighthawki - Wednesday, March 12, 2014 - link

    Another person clueless about this stuff. DX11 isn't just a couple features, it's a new API. DX11 rewrote the entire API to be more efficient, and has a feature know as hardware downleveling. The DX11 runs 100% fine on DX9 and above hardware, and provides much better CPU performance than the same game or application written in DX9.
  • Despoiler - Wednesday, March 12, 2014 - link

    It's funny that you call people clueless. DX11 is a superset of DX10. DX10 was the rewrite of the API. DX9 is its own API. DX9 hardware cannot not run DX10/11 games. If it could there would be such a thing as forward compatibility in GPUs.
  • inighthawki - Wednesday, March 12, 2014 - link

    Yes, DX10 was the rewrite, but nobody uses it so I simplified the argument to not bother with it.

    But you are incorrect. DX9 hardware DOES run DX9 games. DX 10.1 introduced feature levels (hardware downleveling) allowing 9_1 (DX 9.0a, shader model 2.0) hardware to target the 10.1+ API. A game can be written in 100% DX11 code and still run on DX9 hardware while taking advantage of API and performance improvements. DX11 has less overhead in a number of calls over DX9, so there is a huge advantage to using the DX11 API over the 9 API.

    You should probably learn about the thing you're referring to before trying to make a counter argument:
  • inighthawki - Wednesday, March 12, 2014 - link

    Sorry, that should read: "But you are incorrect. DX9 hardware DOES run DX11 games."
  • Despoiler - Wednesday, March 12, 2014 - link

    That's not what you said. You said "DX11 runs 100% fine on DX9 and above hardware." That's if the programmers support the feature level 9_1 thru 9_3. So no it's not 100% and you are not running DX11 because that would imply DX11 functionality because you didn't specify the feature level. Reading comprehension is not your friend today. Also, if game devs support DX9, which means they support XP, which Microsoft doesn't even support, they just use their DX9 renderer. I'd love to hear examples of DX11 games that implemented DX9 feature levels. They could be out there, I'm just not aware of them.

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