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I've asked some questions about OpenGL recently (example) and sometimes the "OpenGL" tag gets removed, or replaced with "OpenGL-ES". The question may indeed say I am targetting OpenGL-ES, but until the answer is known there is no way to know if the question is indeed ES specific, it may just be a generic OpenGL question.

In my view this would be akin to, in the C++ realm, to a questioner saying they use "Visual Studio" and thus the "C++" tag would be dropped. This would be wrong if the question is actually about C++. Or this might be more similar to saying you wish to have a "C++03" answer and the "C++" tag is dropped.

My problem is that the moment the "OpenGL" tag is dropped, people capable of answering GL questions, but who don't follow the specific sub-tags, will no longer see the question. Yet they might be able to answer the question since it could be a generic OpenGL question.

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3 Answers

I'm not sure what the question is here.

Regarding the question you point to, you specifically state in the question

I'm targetted some devices with only OpenGL ES 2.0 support.

so it's proper to retag that for OpenGL ES. OpenGL ES and OpenGL, while sharing a name, are very different animals. OpenGL ES really isn't a subset of OpenGL, so it isn't appropriate to tag everything that targets the former API with the latter. A better example of a subset tag would be the relationship between and .

Solutions may be very different for something related to OpenGL than for OpenGL ES, and the audiences of experts for those questions may also differ. If you have a problem that reaches across both APIs (cross-platform rendering, etc.), then it would be fine to tag with both. Otherwise, it's best to tag with only your target API so that you draw the attention of the right people and get the most appropriate answers for your problem.

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But OpenGL-ES and OpenGL-3 share the majority of their API with each other, especially if you consider core profile only. That is, there is a very good chance that answers to OpenGL-ES questions are fully compatible with OpenGL-3, and vice versa. –  edA-qa mort-ora-y Aug 27 '12 at 16:37
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@edA: Have you actually looked at the OpenGL 3.x API? Because it's got a lot of stuff that ES 2.0 does not have. Conditional rendering, query objects, etc. Yes, ES 2.0 has extensions for those, some of which are widely implemented. But there are features of 3.0 (integer textures, for example) that are not widely implemented. –  Nicol Bolas Aug 27 '12 at 16:44
    
@NicolBolas, I agree, but then the core profile for 3 drops a lot of OpenGL 1.0 stuff, so if a question is labelled OpenGL3 should the generic OpenGL tag be dropped? –  edA-qa mort-ora-y Aug 27 '12 at 16:45
    
@edA: No more than you need to drop the ES tag if you're asking about ES 2.0. –  Nicol Bolas Aug 27 '12 at 16:46
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@edA-qamort-ora-y - On the Apple side of things, we have [cocoa] and [cocoa-touch]. One is designed for the Mac desktop, the other for mobile iOS devices. While they share a common heritage, so much is different between them that one isn't really considered a subset of the other. This is the case with OpenGL and OpenGL ES. People who are experts with one may struggle with the other, and answers may be wildly different depending on the platform involved. If someone really wants to answer questions for both sides, they can easily watch both tags. [opengl] is not an appropriate catch-all here. –  Brad Larson Aug 27 '12 at 16:57
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The question may indeed say I am targetting OpenGL-ES, but until the answer is known there is no way to know if the question is indeed ES specific, it may just be a generic OpenGL question.

There is no "generic OpenGL". There is the OpenGL specification, and the OpenGL ES specification. They are two separate documents that describe similar, but different rendering systems.

Either your question is about desktop OpenGL or about OpenGL ES. It might be about both, but that would be true for tasks like porting from one to the other. You should tag your question with what you're asking about.

My problem is that the moment the "OpenGL" tag is dropped, people capable of answering GL questions, but who don't follow the specific sub-tags, will no longer see the question.

If someone follows the tag, but doesn't follow the tag, then it would be because they're skilled in desktop GL, not in GL ES. And therefore, they don't want to be bothered with questions asking for GL ES solutions.

Take your question for example. If it had the tag, I would answer it like this:

Use glMultiDrawArrays, such that you pick different streams of quads to render.

I would feel comfortable providing that answer because desktop GL has had glMultiDrawArrays since version 1.4. It's commonly available on just about every desktop GL implementation.

However, OpenGL ES 2.0 does not offer this function. And the only reason I even know that is because I just now looked it up. So if you didn't say that you were looking for an ES solution, my answer would have wasted both of our time.

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But you, as an OpenGL expert, may very well know a solution which happens to work in ES as well. –  edA-qa mort-ora-y Aug 27 '12 at 16:46
    
By the same logic somebody well versed in OpenGL 1.0 may not be able to answer questions for OpenGL 3.0, as a lot of the API they know is no longer supported. –  edA-qa mort-ora-y Aug 27 '12 at 16:47
    
@edA: And, as in the case of this very question, I might not. As for the core/compatibility distinction, we have a tag asking specifically for core solutions. The rest can be inferred from the question (if someone asks about shader stuff, replying with fixed-function is not helpful). –  Nicol Bolas Aug 27 '12 at 16:49
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I'll make my answer with a viewpoint as to why such tag dropping should not occur. There are lots of such tags, not related to just OpenGL, where there are a few versions, or a technology branches and there is a large overlap. Consider what happens when we allow dropping of tags.

If a user knows their specific tags will be dropped they will simply stop adding such tags. Instead of mentioned important things like which version they are using, which compiler they are using, which environment, they'll just leave it entirely open and select an answer appropriately. This would be very bad since the question now leaves out vital information, information the questioner was willing to provide.

Consider in my case I could just have easily dropped the comment saying I am targetting OpenGL-ES. In that case there would be no option but to leave the generic "OpenGL" tag. If there is an answer incompatible with ES, then I've just wasted that answerers time. Yet if there is an answer compatilbe with ES, then great for me. That is, I don't lose anything by not providing the additional information/tags.

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"If a user knows their specific tags will be dropped they will simply stop adding such tags." That's good, because quite frankly I'm tired of frequently removing the "opengl" tag from questions asking about ES. –  Nicol Bolas Aug 27 '12 at 16:46
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"there would be no option but to leave the generic "OpenGL" tag" Your option would be to tag it "opengl-es". Like it is now. –  Nicol Bolas Aug 27 '12 at 16:47
    
No, I'd be prone to drop all references to ES and simply label it as OpenGL. I wouldn't drop the generic tag, only the specifc ones. –  edA-qa mort-ora-y Aug 27 '12 at 16:49
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Let me make this clear to you: OpenGL is not a generic tag! It is a tag that refers to a specific series of specifications. Ones that are not covered by any of the ES specifications. –  Nicol Bolas Aug 27 '12 at 16:49
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