Is OpenGL enough or should I also support DirectX?

If you're wanting to target android, ios, mac and linux, you have no ability to use directx on these platforms.

OpenGL will be enough unless you want to learn directx just because it's there, however please note that these different platforms have slightly different forms of OpenGL with different extensions available, which perform differently with differing code. For example the mobile platforms almost exclusively use OpenGL ES rather than the full OpenGL, and within OpenGL there are several versions, depending upon the age of the system you want to target.

Hope this helps!

From a pure portability point of view, you only need OpenGL (and really don't have much of a choice anyway on all named platforms but Windows). There are other reasons to support several backends, though.

It's getting less of an issue these days, but there used to be a good reason to support DirectX anyway under Windows if you already had an OpenGL backend: Driver quality.

Though AMD has stopped shipping shit cards with crap drivers a long time ago (they're not rarely better than nVidia now) and even Intel seems to at least try to produce something halfway sane, up-to-date, and standards-conformant in the mean time. I remember reading Intel even supports the full set of OpenGL 4.3 now (which is kind of a miracle).

If you're wanting to target android, ios, mac and linux, you have no ability to use directx on these platforms.

OpenGL will be enough unless you want to learn directx just because it's there, however please note that these different platforms have slightly different forms of OpenGL with different extensions available, which perform differently with differing code. For example the mobile platforms almost exclusively use OpenGL ES rather than the full OpenGL, and within OpenGL there are several versions, depending upon the age of the system you want to target.

Hope this helps!

Yea it helps. Thank you! :)

Some more questions:

1. Some people say DirectX has less gotchas and headaches than OpenGL on windows. Some also say OpenGL has worse drivers than DirectX. What exactly are they referring to? Will there be any problems or is there anything I need to be aware if I use OpenGL on windows?

2. I hope to support almost every machine, including those very old PC (about 10 years old I guess?) Since I am making a 2D engine, I don't need many advanced features. Is OpenGL ver. 2.0 my best option or should I use a later version?

From a pure portability point of view, you only need OpenGL (and really don't have much of a choice anyway on all named platforms but Windows). There are other reasons to support several backends, though.

It's getting less of an issue these days, but there used to be a good reason to support DirectX anyway under Windows if you already had an OpenGL backend: Driver quality.

Though AMD has stopped shipping shit cards with crap drivers a long time ago (they're not rarely better than nVidia now) and even Intel seems to at least try to produce something halfway sane, up-to-date, and standards-conformant in the mean time. I remember reading Intel even supports the full set of OpenGL 4.3 now (which is kind of a miracle).

Haha I like your stories.

Yea driver quality, that was what I was trying to ask. The point is that I want to support old machines. I wonder if driver can be an issue if I use OpenGL?

Also, I hope to support almost every machine, including those very old PC (about 10 years old I guess?) Since I am making a 2D engine, I don't need many advanced features. Is OpenGL ver. 2.0 my best option or should I use a later version?

1. Some people say DirectX has less gotchas and headaches than OpenGL on windows. Some also say OpenGL has worse drivers than DirectX. What exactly are they referring to? Will there be any problems or is there anything I need to be aware if I use OpenGL on windows?

Yes. You can use DirectX directly on windows, while with OpenGL you have to eigther import the DLL commands yourself (don't do it), or use an external wrapper libary like GLEW, to even be able to do anything with it. Also with DirectX you can directly use your created Windows hWnd, while in OpenGL you must configure your window to have a special HDC and use that. Other than that, using OpenGL is not that much different than using it on any other platform (supposed you even write the application creation code yourself and don't use SFML or what not). In any way this is NO reason to use DirectX on Windows if you already have an OpenGL renderer.

2. I hope to support almost every machine, including those very old PC (about 10 years old I guess?) Since I am making a 2D engine, I don't need many advanced features. Is OpenGL ver. 2.0 my best option or should I use a later version?

Recent OpenGL version have a very bad support rate, I know PCs from < 3 years ago that don't even support 3.4 or whatnot. As for features, if you are making a 2D game, there are not that many of use for you anyways. The wikipedia-page on OpenGL has a full list of it, but I don't see what you could really need. For example, I decided to require at least OpenGL 3.1 as they introduced uniform buffer objects which tied in with my pipeline much more (otherwise I'd have to redesign that), but you shouldn't need that. So OpenGL 2.0 should be just fine.

If you want to support "10+ year old" cards (such as NV30/Geforce FX, or R300/Radeon-9000), you are stuck with OpenGL 2, yes. Though all cards that can support 2.0 can support 2.1 as well (presumed that the driver is up-to-date). This adds pixel buffer object functionality, which may be interesting if you have a lot of sprites to upload for your 2D game.

I would personally never touch anything less than OpenGL 3 again in my life, which is supported by 9 year old graphics cards (such as Geforce 8). The reason not being that the additional hardware functionality is that much useful in comparison, but simply that OpenGL 2.0 is a nightmare to get going with three dozen extensions that you need for some of the most basic things, and no sane guarantees on texture sizes and such. Almost every graphics card, even 15-16 year old ones, can do more than the bare minimum, but given no minimum guarantees you don't know for sure unless you spend considerable work querying (you can't even be sure that you can use a 512-texture).

OpenGL 3 on the other hand, comes with sane (not great, but OK) minimum guarantees and provides almost all functionality that you need, for 90% of everything you will ever be doing in your life (for the other 10% you'll need GL4).

On Windows, do you want to support machines that probably never had a GPU driver update installed, and whose users don't even know how to update drivers? If the answer is yes, you pretty much need to default to DirectX on Windows.

On Windows, do you want to support machines that probably never had a GPU driver update installed, and whose users don't even know how to update drivers? If the answer is yes, you pretty much need to default to DirectX on Windows.

Ugh... those users are a nightmare by themselves. I wouldn't want them as customers. Even if they pay you (chances are they don't, otherwise they'd not have a computer that they pulled out of the trash can), they cannot possibly pay you enough for the support cost they will cause.

On Windows, do you want to support machines that probably never had a GPU driver update installed, and whose users don't even know how to update drivers? If the answer is yes, you pretty much need to default to DirectX on Windows.

Ugh... those users are a nightmare by themselves. I wouldn't want them as customers. Even if they pay you (chances are they don't, otherwise they'd not have a computer that they pulled out of the trash can), they cannot possibly pay you enough for the support cost they will cause.

True. My customers have to know how to follow instructions at least.
It seems OpenGL 2.1 is really bad and can potentially cause a lot of problems?

1. Some people say DirectX has less gotchas and headaches than OpenGL on windows. Some also say OpenGL has worse drivers than DirectX. What exactly are they referring to? Will there be any problems or is there anything I need to be aware if I use OpenGL on windows?

Yes. You can use DirectX directly on windows, while with OpenGL you have to eigther import the DLL commands yourself (don't do it), or use an external wrapper libary like GLEW, to even be able to do anything with it. Also with DirectX you can directly use your created Windows hWnd, while in OpenGL you must configure your window to have a special HDC and use that. Other than that, using OpenGL is not that much different than using it on any other platform (supposed you even write the application creation code yourself and don't use SFML or what not). In any way this is NO reason to use DirectX on Windows if you already have an OpenGL renderer.

2. I hope to support almost every machine, including those very old PC (about 10 years old I guess?) Since I am making a 2D engine, I don't need many advanced features. Is OpenGL ver. 2.0 my best option or should I use a later version?

Recent OpenGL version have a very bad support rate, I know PCs from < 3 years ago that don't even support 3.4 or whatnot. As for features, if you are making a 2D game, there are not that many of use for you anyways. The wikipedia-page on OpenGL has a full list of it, but I don't see what you could really need. For example, I decided to require at least OpenGL 3.1 as they introduced uniform buffer objects which tied in with my pipeline much more (otherwise I'd have to redesign that), but you shouldn't need that. So OpenGL 2.0 should be just fine.

Thank you for your reply. I'll consider about that.

Android/iOS don't use GL, they use GL|ES (version 1/2/3).
Desktops use GL (version 1/2/3/4).
Version 1 of both is old enough to forget about.

Also, GL and GL|ES are API specifications, not libraries (API implementations).
There's a lot of implementations of the spec --
On Windows, there's one each from Intel/AMD/nVidia. On Mac and iPhone, Apple has a standard one (GL for desktop, GL|ES for iOS). Linux is similar situation to Windows, but there's also some community/open-source implementations too. On Android, every damn phone manufacturer has their own implementations.

Whenever you have a common specification, but dozens of implementations, someone always fucks up some of the details, or bends the rules, or extends them, or breaks them on purpose.
That's the unavoidable situation for GL (and HTML renderers, or COLLADA exporters, etc).

In a web-page, or a GL renderer, you will end up with some platform/implementation specific tweaks / workarounds / ugly hacks.

The reason this gets brought up in contrast to D3D, is that (each version of) D3D has a single implementation.
Sure - underneath Windows+D3D and under Apple+GL there's another spec (the driver model) which has to be implemented by Intel/AMD/nVidia -- but the difference here is that there is a gatekeeper. MS/Apple can test driver implementations and reject ones that fail to comply with the spec. This means that D3D+Windows and GL+Apple tend to be very stable and correct, but GL on Windows/Linux have no guarantees, and GL|ES on Android is a clusterfuck.

If you're fine with fairly old rendering techniques (no constant buffers, just shader uniforms, no VAO's) I wouldn't call OpenGL 2.0 or 2.1 bad. It has a fairly straightforward mapping to OpenGL ES 2.0, meaning your rendering code won't differ that much between desktop & mobile, and because it's older, it's better guaranteed to work with older drivers. You'll just need to be strict with obeying even the "stupid" parts of the specs, like for example if you use multiple render targets with a FBO, make sure they are the same color format.

If you use only GL ES 2 you can try use https://code.google.com/p/angleproject/ to get the benefits of D3D (consistency/stability) without using it yourself.

I've never tried it myself, but if it works for Chromium itself it must be good enough.

Id tech is one notable AAA company that uses GL, but that is largely historical.

Some/most graphic engines abstract away GL/D3D part into a common API so you mostly don't care about which one is running, and this is what any sane engine should do so rest of the code is both independent of that and not trashed by GLuint and other fun types and macros being in the headers and the API.

Doom 3 BFG actually used 3 APIs: one for PS (Sony's NDA low level one), one for XBox (DirectX) and one for Windows (GL), they too wrapped them in common API in own code while original Doom 3 was PC only with GL only.

A frequently-overlooked issue is tools support. Direct3D has fabulous tools. OpenGL has mediocre tools. When it comes to debugging why nothing's rendering, or why buffers seemingly have the wrong value, or why your shaders aren't doing what you expect, those tools all come in extremely handy. I highly recommend writing all your initial code in Direct3D and then - once you know your code is correct and working properly - porting it to GL afterwards. If you are smart and abstract your drawing code (nothing but the renderer itself should ever touch D3D/GL) then porting is often something you can do in a few days for most indie/hobby games.

So far as portability, GL is also an incomplete story. Some OSes force you to use GLES, some force you to use GL Core to get modern features, some OSes still have stone-aged drivers, some platforms are pushing new proprietary APIs and potentially abandoning GL, some platforms have never had GL in the first place. If you care about maximum portability or just learning how to do graphics like The Pros, you need to accept that you need multiple backend renderers that target different APIs. Or even more confusingly, that target the same API but with wildly different feature sets (GL 2 vs GL 4, mobile vs desktop use of GLES/WebGL, etc.).

To echo Sean... As an example many newer programmers don't know how or what kind of images should be loaded from disk. With DirectX there's some convenient functions for loading (for example) PNG files without using zlib/pnglib, so it's largely a non-issue when using DX. With OpenGL all images will need to be loaded with some additional code since no utility functions are given by GL.

As an example many newer programmers don't know how or what kind of images should be loaded from disk. With DirectX there's some convenient functions for loading (for example) PNG files without using zlib/pnglib

Not just that, but in DirectX there is the dds format which can hold texture arrays, texture cubes, mipmaps, and all sorts of other stuff in one convenient container format. For directx definitely investigate it...

Not just that, but in DirectX there is the dds format which can hold texture arrays, texture cubes, mipmaps, and all sorts of other stuff in one convenient container format. For directx definitely investigate it...

You can use it with GL too; it's only a container format and the data payload is the same whatever graphics API you are using.

Really .dds should be your first stop when loading game ready textures, it can handle everything you graphics card can after all.
PNG and TGA are source images and shouldn't be anywhere near your final game.

You can use it with GL too; it's only a container format and the data payload is the same whatever graphics API you are using.

Yes true, the down side is that outside of windows you'll need a third party library to load dds files or its a case of roll your own. It's a feature rich format which I wouldn't fancy creating a parser for myself. Best to stick to windows for that IMHO and leverage that particular advantage...

Since vulkan is coming out, DirectX will probably become obsolete. You can also do anything in DirectX in OpenGL + extensions. It's just not as easy.