11 ms·

Why you should do OpenGL and not DirectX

192 points by zitterbewegung 17y ago

Dilpil 17y ago
I was under the impression that DirectX was a more extensive API, and included support for more complex high level operations- is this untrue?
- psadauskas 17y ago
  Yes, the article says this is untrue. It specifically mentions features that OpenGL has had years before DirectX.
  - daeken 17y ago
    Well, no, the article points out a few specific cases where it's untrue, but there are a few things that need to be pointed out here. Extensions like tessellation aren't guaranteed to be there, and if they aren't you have to implement this yourself. It also ignores the shader/effect pipeline, which you effectively have to build yourself in OpenGL, unless you use Cg. As I noted in my first comment here, these are strengths of OpenGL in some cases, but are big negatives in others.
    - rbanffy 17y ago
      "and if they aren't you have to implement this yourself." Either that or offer a slightly degraded gaming experience according to what the OpenGL system exposes. Nobody cares that much if their phone can't show the same tessellation glory their kid's dual-GPU oil-cooled deskside monster can.
    - ajross 17y ago
      Tesselation is a hardware feature. It's not an API extension. It's not "guaranteed to be there" ever. Any app that wants to use it needs to test for its presence. How are the D3D and OpenGL mechanisms not completely isomorphic? And OpenGL has had a standard shader language since v2.0, about 6-7 years ago? You don't have to "build it yourself" except in the sense of having to port DX shaders to a slightly different source language.
- astine 17y ago
  "DirectX" is an umbrella term that covers a lot of low level APIs. OpenGL is just a 3D graphics layer (good one) while DirectX does many things including 2D, IO and sound. Now it seems as if the author is only comparing OpenGL to Direct3D, but he doesn't make that clear.
  - witten 17y ago
    Minor correction: OpenGL actually works great for 2D as well. There are versions of all the API functions that accept vertices with 2 dimensions instead of 3. And you can quite easily make vertex buffer objects with only 2 dimensions.
    - daeken 17y ago
      You have the ortho modes and all that, but that's not really 2d drawing. Doing things like concave shapes with specific line drawing (especially if you want decent anti-aliasing) is complex and expensive, since OpenGL isn't particularly well suited for it. Of course, on the DirectX side you have the DirectDraw vs Direct2D mess, not to mention that the APIs are very poorly designed (in my opinion, at least). Doing 2D stuff in OpenGL isn't terrible, but it's certainly not well suited to it. In most cases, something like SDL ends up being easier and rarely too much slower (well, unless you're scaling/rotating...).
      - witten 17y ago
        It's true that OpenGL doesn't have built-in support for things like concave shapes, but you can always do tessellation and feed GL triangles. (Some tessellation options were mentioned in the article.) I've found that for my particular uses, the hardware acceleration you get with GL makes it worth it for 2D, even if it's perhaps not otherwise as well-suited for that as SDL.
        daeken 17y ago
        You know, this makes me think. Are there any good 2D libraries for OpenGL? I've seen a few, but they all seemed very special-purpose or were either poorly designed or just didn't work. It'd be interesting to have a nice library like SDL, but sitting on top of real hardware acceleration.
- maxklein 17y ago
  DirectX has a lot of sub sections - DirectShow for media playback, DirectSound for audio stuff and so on. For graphics, there is Direct3D and some other stuff I know too little about.
daeken 17y ago
This is sort of a loaded article, since it glances over the benefits of DirectX. (Note: I'm an OpenGL developer, but I worked on implementing D3D10 on top of OpenGL, and I've worked with DX7+ over the years. I'm not a fan, but leaving these things out is misleading.) First and foremost, it's wrong to compare OpenGL and DirectX, rather than OpenGL and Direct3D. OpenGL directly competes with a small portion of Direct3D, and requires several libraries (I'm a big fan of SDL, OpenAL, etc myself) to begin to touch the breadth of DX. Second, with OpenGL you have many vendors producing extensions and implementing them at different times. With Direct3D, you have a single set of features you write for which are guaranteed to be there (in a given version). This means that when you write code for OpenGL, you have to special-case paths for many different available extensions and duplicate many pieces of functionality. If you want to use shaders, you have to either make your own effects system on top of GLSL/ARB shaders or use something like Cg. The Direct3D effects pipeline saves a lot of time, but of course reduces flexibility. In the end, the call on OGL vs DX really comes down to these things: How much do you care about cross-platform compatibility? How much time do you have to put into your engine? Do you want complete flexibility w.r.t. your rendering pipeline? If you're an engine-tech-heavy firm, OpenGL will almost always be the right choice. If you're just making a game, DirectX will almost definitely save you time. Again, I'm not a DX fan, but it has its place, and this sort of article is woefully misleading.
- city41 17y ago
  OpenGL only competing against a portion of DirectX can be seen as a plus or a minus. I like the fact that OpenGL focuses on one thing and tries to "do one thing and do it well."
  - daeken 17y ago
    As do I, but it certainly increases the cost of development on a production engine. Personally, I like that; it gives me about as low-level control as possible, which is great, but it's certainly not for everyone.
  - snprbob86 17y ago
    DirectX is an umbrella brand. Direct3D is the equivalent of OpenGL. Most of the Direct3D developers don't even bother to checkout the source code for the other DirectX components.
smallblacksun 17y ago
I was hoping for a good comparison of the two, and instead got a typical fanboy rant. There are a few good points, too bad they are buried.
- barrkel 17y ago
  I rather see it as an attempt at a manifesto, a call to action, to point out the risks of blindly following MS too closely.
  - daeken 17y ago
    The danger here, though, is in writing a blatantly misleading article clearly targeting those developers that would be better suited by DirectX, generally. Developers doing the sort of complex work that OpenGL is particularly well suited for (tech-heavy engine development, wherein total control is useful) tend to know that they need OpenGL. Developers just looking to write a game would often be better served by using DirectX, and leaving out the (very real) benefits of DirectX/3D is just downright misleading.
snprbob86 17y ago
I wrote a big comment about OpenGL vs Direct3D with a bit of a historical as well as future looking perspective here: http://news.ycombinator.com/item?id=593801 http://news.ycombinator.com/item?id=593801 In summary, OpenGL is an abstraction of 3D concepts with many vendor-specific extensions to enable performance. Direct3D is an abstraction of the most common implementation of real world 3D hardware. Game developers did, and continue to, unambiguously ask Microsoft to produce the latter. I understand the graphics pipeline pretty deeply if anyone needs some clarification.
akamaka 17y ago
Don't read. This article is simply a manifesto calling for developers to use OpenGL. The mindset of the author is firmly locked in the late-1990s, which was the height of the OpenGL vs. DirectX flamewars. I'm amazed that he didn't bring up Fahrenheit. (http://en.wikipedia.org/wiki/Fahrenheit_graphics_API http://en.wikipedia.org/wiki/Fahrenheit_graphics_API) The accusations about Direct3D gaining dominance because of FUD or some other nefarious actions are pretty ridiculous. Graphics APIs evolved rapidly during the period between 1998-2005, and there were times when Direct3D had a clear technology lead in certain areas. I've never met a single graphics developer who switched away from OpenGL for any reason other than preferring to work with D3D. However, the balance has stabilized in recent years, and the author of this article doesn't tell us anything useful about current technology.
- stevejohnson 17y ago
  The rest of the article aside, I think that avoiding MS lock-in is a great reason to use OpenGL over Direct3D.
  - akamaka 17y ago
    Lock-in is definitely a big concern, but the article vastly overstates the cross-platform benefits of OpenGL. Different platforms have different capabilities and limitations, and most of the work in creating high-performance 3D software involves optimizing for specific hardware. For example, porting an OpenGL-based game from Windows to the PS3 would not be significantly easier than porting a D3D-based X-Box game.
    - dazzawazza 17y ago
      FWIW: SCEA provide an implementation of OpenGL for PS3 so it should be 'easier'. I've heard it's not that fast given the strange nature of the PS3 hardware pipeline but it might be fast enough.
      - deleted 17y ago
        [deleted]
jsz0 17y ago
Can anyone comment on how Open GL ES plays into this? It seems to be the defacto standard for SmartPhones and that market is going to continue to grow rapidly. Is that going to influence OGL's adoption elsewhere? Or are there other factors that make that irrelevant?
- jcl 17y ago
  I doubt portable games would affect OpenGL's use on the desktop directly. Games on the major consoles are typically not ported to portables and vice versa, so the two markets will remain segregated. And while console games are frequently ported to PC, portable games are not -- although perhaps this will change with the adoption of WebGL mentioned in the article. In any case, portable games will not directly help the performance, stability, or feature-richness of desktop OpenGL drivers in the way that console games help desktop Direct3D drivers. That said, one way that portable games could contribute to the general advancement of OpenGL is by being the first platform that new programmers learn. A typical console game requires significant coding experience and artistic assets to compete, while the expectations (and costs) for a portable or web game are much lower, making such a game a more appealing target for a beginning programmer. And perhaps those programmers will continue to use OpenGL when they go on to make desktop games.
amitt 17y ago
Having used both and worked at companies that make 3d engines as their main product, I've seen that one good way to approach this problem is to simply abstract away the API into a common interface that can be swapped between. At a high level, the concepts that both APIs provide arent that unsimilar and abstraction is possible even if you are using some of the more esoteric features of each.
McP 17y ago
Ignore the article. I'm an OpenGL developer but I would dearly love to use Direct3D instead - Direct3D has a very nice API and is well supported on all graphics cards, while OpenGL is a mess of extensions and only works well on Nvidia GPUs (and maybe ATI). The only reason we use OpenGL is for independence from Windows.

192 points by zitterbewegung 17y ago

I was under the impression that DirectX was a more extensive API, and included support for more complex high level operations- is this untrue?

psadauskas 17y ago
Yes, the article says this is untrue. It specifically mentions features that OpenGL has had years before DirectX.
- daeken 17y ago
  Well, no, the article points out a few specific cases where it's untrue, but there are a few things that need to be pointed out here. Extensions like tessellation aren't guaranteed to be there, and if they aren't you have to implement this yourself. It also ignores the shader/effect pipeline, which you effectively have to build yourself in OpenGL, unless you use Cg. As I noted in my first comment here, these are strengths of OpenGL in some cases, but are big negatives in others.
  - rbanffy 17y ago
    "and if they aren't you have to implement this yourself." Either that or offer a slightly degraded gaming experience according to what the OpenGL system exposes. Nobody cares that much if their phone can't show the same tessellation glory their kid's dual-GPU oil-cooled deskside monster can.
  - ajross 17y ago
    Tesselation is a hardware feature. It's not an API extension. It's not "guaranteed to be there" ever. Any app that wants to use it needs to test for its presence. How are the D3D and OpenGL mechanisms not completely isomorphic? And OpenGL has had a standard shader language since v2.0, about 6-7 years ago? You don't have to "build it yourself" except in the sense of having to port DX shaders to a slightly different source language.
astine 17y ago
"DirectX" is an umbrella term that covers a lot of low level APIs. OpenGL is just a 3D graphics layer (good one) while DirectX does many things including 2D, IO and sound. Now it seems as if the author is only comparing OpenGL to Direct3D, but he doesn't make that clear.
- witten 17y ago
  Minor correction: OpenGL actually works great for 2D as well. There are versions of all the API functions that accept vertices with 2 dimensions instead of 3. And you can quite easily make vertex buffer objects with only 2 dimensions.
  - daeken 17y ago
    You have the ortho modes and all that, but that's not really 2d drawing. Doing things like concave shapes with specific line drawing (especially if you want decent anti-aliasing) is complex and expensive, since OpenGL isn't particularly well suited for it. Of course, on the DirectX side you have the DirectDraw vs Direct2D mess, not to mention that the APIs are very poorly designed (in my opinion, at least). Doing 2D stuff in OpenGL isn't terrible, but it's certainly not well suited to it. In most cases, something like SDL ends up being easier and rarely too much slower (well, unless you're scaling/rotating...).
    - witten 17y ago
      It's true that OpenGL doesn't have built-in support for things like concave shapes, but you can always do tessellation and feed GL triangles. (Some tessellation options were mentioned in the article.) I've found that for my particular uses, the hardware acceleration you get with GL makes it worth it for 2D, even if it's perhaps not otherwise as well-suited for that as SDL.
      - daeken 17y ago
        You know, this makes me think. Are there any good 2D libraries for OpenGL? I've seen a few, but they all seemed very special-purpose or were either poorly designed or just didn't work. It'd be interesting to have a nice library like SDL, but sitting on top of real hardware acceleration.
maxklein 17y ago
DirectX has a lot of sub sections - DirectShow for media playback, DirectSound for audio stuff and so on. For graphics, there is Direct3D and some other stuff I know too little about.

daeken 17y ago

This is sort of a loaded article, since it glances over the benefits of DirectX. (Note: I'm an OpenGL developer, but I worked on implementing D3D10 on top of OpenGL, and I've worked with DX7+ over the years. I'm not a fan, but leaving these things out is misleading.) First and foremost, it's wrong to compare OpenGL and DirectX, rather than OpenGL and Direct3D. OpenGL directly competes with a small portion of Direct3D, and requires several libraries (I'm a big fan of SDL, OpenAL, etc myself) to begin to touch the breadth of DX. Second, with OpenGL you have many vendors producing extensions and implementing them at different times. With Direct3D, you have a single set of features you write for which are guaranteed to be there (in a given version). This means that when you write code for OpenGL, you have to special-case paths for many different available extensions and duplicate many pieces of functionality. If you want to use shaders, you have to either make your own effects system on top of GLSL/ARB shaders or use something like Cg. The Direct3D effects pipeline saves a lot of time, but of course reduces flexibility. In the end, the call on OGL vs DX really comes down to these things: How much do you care about cross-platform compatibility? How much time do you have to put into your engine? Do you want complete flexibility w.r.t. your rendering pipeline? If you're an engine-tech-heavy firm, OpenGL will almost always be the right choice. If you're just making a game, DirectX will almost definitely save you time. Again, I'm not a DX fan, but it has its place, and this sort of article is woefully misleading.

city41 17y ago
OpenGL only competing against a portion of DirectX can be seen as a plus or a minus. I like the fact that OpenGL focuses on one thing and tries to "do one thing and do it well."
- daeken 17y ago
  As do I, but it certainly increases the cost of development on a production engine. Personally, I like that; it gives me about as low-level control as possible, which is great, but it's certainly not for everyone.
- snprbob86 17y ago
  DirectX is an umbrella brand. Direct3D is the equivalent of OpenGL. Most of the Direct3D developers don't even bother to checkout the source code for the other DirectX components.

smallblacksun 17y ago

I was hoping for a good comparison of the two, and instead got a typical fanboy rant. There are a few good points, too bad they are buried.

barrkel 17y ago
I rather see it as an attempt at a manifesto, a call to action, to point out the risks of blindly following MS too closely.
- daeken 17y ago
  The danger here, though, is in writing a blatantly misleading article clearly targeting those developers that would be better suited by DirectX, generally. Developers doing the sort of complex work that OpenGL is particularly well suited for (tech-heavy engine development, wherein total control is useful) tend to know that they need OpenGL. Developers just looking to write a game would often be better served by using DirectX, and leaving out the (very real) benefits of DirectX/3D is just downright misleading.

snprbob86 17y ago

I wrote a big comment about OpenGL vs Direct3D with a bit of a historical as well as future looking perspective here: http://news.ycombinator.com/item?id=593801 http://news.ycombinator.com/item?id=593801 In summary, OpenGL is an abstraction of 3D concepts with many vendor-specific extensions to enable performance. Direct3D is an abstraction of the most common implementation of real world 3D hardware. Game developers did, and continue to, unambiguously ask Microsoft to produce the latter. I understand the graphics pipeline pretty deeply if anyone needs some clarification.

akamaka 17y ago

Don't read. This article is simply a manifesto calling for developers to use OpenGL. The mindset of the author is firmly locked in the late-1990s, which was the height of the OpenGL vs. DirectX flamewars. I'm amazed that he didn't bring up Fahrenheit. (http://en.wikipedia.org/wiki/Fahrenheit_graphics_API http://en.wikipedia.org/wiki/Fahrenheit_graphics_API) The accusations about Direct3D gaining dominance because of FUD or some other nefarious actions are pretty ridiculous. Graphics APIs evolved rapidly during the period between 1998-2005, and there were times when Direct3D had a clear technology lead in certain areas. I've never met a single graphics developer who switched away from OpenGL for any reason other than preferring to work with D3D. However, the balance has stabilized in recent years, and the author of this article doesn't tell us anything useful about current technology.

stevejohnson 17y ago
The rest of the article aside, I think that avoiding MS lock-in is a great reason to use OpenGL over Direct3D.
- akamaka 17y ago
  Lock-in is definitely a big concern, but the article vastly overstates the cross-platform benefits of OpenGL. Different platforms have different capabilities and limitations, and most of the work in creating high-performance 3D software involves optimizing for specific hardware. For example, porting an OpenGL-based game from Windows to the PS3 would not be significantly easier than porting a D3D-based X-Box game.
  - dazzawazza 17y ago
    FWIW: SCEA provide an implementation of OpenGL for PS3 so it should be 'easier'. I've heard it's not that fast given the strange nature of the PS3 hardware pipeline but it might be fast enough.
    - deleted 17y ago
      [deleted]

jsz0 17y ago

Can anyone comment on how Open GL ES plays into this? It seems to be the defacto standard for SmartPhones and that market is going to continue to grow rapidly. Is that going to influence OGL's adoption elsewhere? Or are there other factors that make that irrelevant?

jcl 17y ago
I doubt portable games would affect OpenGL's use on the desktop directly. Games on the major consoles are typically not ported to portables and vice versa, so the two markets will remain segregated. And while console games are frequently ported to PC, portable games are not -- although perhaps this will change with the adoption of WebGL mentioned in the article. In any case, portable games will not directly help the performance, stability, or feature-richness of desktop OpenGL drivers in the way that console games help desktop Direct3D drivers. That said, one way that portable games could contribute to the general advancement of OpenGL is by being the first platform that new programmers learn. A typical console game requires significant coding experience and artistic assets to compete, while the expectations (and costs) for a portable or web game are much lower, making such a game a more appealing target for a beginning programmer. And perhaps those programmers will continue to use OpenGL when they go on to make desktop games.

amitt 17y ago

Having used both and worked at companies that make 3d engines as their main product, I've seen that one good way to approach this problem is to simply abstract away the API into a common interface that can be swapped between. At a high level, the concepts that both APIs provide arent that unsimilar and abstraction is possible even if you are using some of the more esoteric features of each.

McP 17y ago

Ignore the article. I'm an OpenGL developer but I would dearly love to use Direct3D instead - Direct3D has a very nice API and is well supported on all graphics cards, while OpenGL is a mess of extensions and only works well on Nvidia GPUs (and maybe ATI). The only reason we use OpenGL is for independence from Windows.