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OpenGL Managing OpenGL Versions

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Greetings everyone,

I'm currently working with a video card that supports GL 4.2 and that is marvelous. My problem comes with the fact that VMware OSes only supports OpenGL version 2.1.

Now, I'm trying to find a way to downgrade my actual code to be 2.1 compatible. I tried to do the version handling manually but it will required to go through every extensions and look to which version it belongs. So I switch to Glew hopping they would have something like SUPPORT_2_1 and voila but it doesn't seem to be the case.

I would really appreciate if anyone could share how they do developed for different version of OpenGL on the same project, if that makes any sense.

Thx

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There is a fundamental difference when going back from 3.3 to 2.1. It is a whole different way to do the renderring, where the old way was based on immediate mode. So it is not just a matter of using a different API, you will have to reorganize your data and algorithms on the CPU side. See [url="http://www.opengl.org/wiki/Legacy_OpenGL"]http://www.opengl.org/wiki/Legacy_OpenGL[/url] for more information.

However, the situation is more complicated than that. I don't know about WMware OS, but it is not unusual for a 2.1 graphics card to actually support functionality from 3.3.

There are two ways to check for extensions in glew. Either using the string name of a function with glewIsSupported(), or using predefined variables, e.g. "if (GLEW_ARB_vertex_program) ..."

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I pick a baseline version, code to that, and just don't support anything below. Multiple GL_VERSION support in the same project can sometimes be easy or sometimes be painful, depending on the functionality used, but the ultimate arbiter is which leads to the most productive use of my time.

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I'm pretty sure that any VM will fall back into software rendering regardless OpenGL spec. So even if you port your code for 2.1, it will be unusable.

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At least VirtualBox has (experimental) support for hardware 3D accelaration:
[quote]With this feature, if an application inside your virtual machine uses 3D features through the OpenGL or Direct3D 8/9 programming interfaces, instead of emulating them in software (which would be slow), VirtualBox will attempt to use your host's 3D hardware. This works for all supported host platforms (Windows, Mac, Linux, Solaris), provided that your host operating system can make use of your accelerated 3D hardware in the first place.[/quote] ([url=http://www.virtualbox.org/manual/ch04.html#guestadd-3d]source[/url])

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Thank you guys for your inputs,

[QUOTE]There is a fundamental difference when going back from 3.3 to 2.1.[/QUOTE]
Yes, of course, I'm very aware of this.

[QUOTE]it is not unusual for a 2.1 graphics card to actually support functionality from 3.3[/QUOTE]

I guess this is where my confusion comes from. If my understanding is correct, GL 2.1 could use 3.3 extensions without implementing 3.1 core?

When going through glcorearb.h [url="http://www.opengl.org/registry/api/glcorearb.h"]here[/url] it seems like they have specific version extensions and floating ones that doesn't belong to any versions in particular, is that correct?

[QUOTE]I'm pretty sure that any VM will fall back into software rendering regardless OpenGL spec. So even if you port your code for 2.1, it will be unusable.[/QUOTE]

Not useable? Anyone could confirm this? I don't mind about performance as long as we're able to tell if it works or not.

I shall give a try to VirtualBox.

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[quote name='TheChubu' timestamp='1354196532' post='5005288']
I'm pretty sure that any VM will fall back into software rendering regardless OpenGL spec. So even if you port your code for 2.1, it will be unusable.
[/quote]

Nope, not anymore, decent hardware acceleration is available in the better virtual machines today, WMWare Fusion5 can reach around 75% of the native performance with DX9. (VirtualBox however is quite far behind still)

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Just because you need to use OpenGL 2.x doesnt mean you need to use immediate mode rendering.

Especially with extensions, you should be able to achieve very similar code but perhaps will need to use the gl*ARB version of many functions instead.

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[quote name='SimonForsman' timestamp='1354202226' post='5005326']
[quote name='TheChubu' timestamp='1354196532' post='5005288']
I'm pretty sure that any VM will fall back into software rendering regardless OpenGL spec. So even if you port your code for 2.1, it will be unusable.
[/quote]

Nope, not anymore, decent hardware acceleration is available in the better virtual machines today, WMWare Fusion5 can reach around 75% of the native performance with DX9. (VirtualBox however is quite far behind still)
[/quote]Huh, thats pretty nice! Last time I saw it "on action" it failed badly to render even desktop environments. Edited by TheChubu

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[quote name='larspensjo' timestamp='1354131778' post='5005047']
There is a fundamental difference when going back from 3.3 to 2.1. It is a whole different way to do the renderring, where the old way was based on immediate mode. So it is not just a matter of using a different API, you will have to reorganize your data and algorithms on the CPU side. See [url="http://www.opengl.org/wiki/Legacy_OpenGL"]http://www.opengl.or...i/Legacy_OpenGL[/url] for more information.
[/quote]
Actually, immediate mode was more of a thing of the 1.x versions. With version 2.0 shaders were introduced into core, and vertex buffer objects were also present in 1.5 if I recall correctly, so you can program in a somewhat similar way to the newer APIs if you stick to shaders and buffers only. Also you won't get geometry shaders.

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The bigger problem about using OpenGL 2.x is that certain things just won't work for sure, and that you don't have any guarantees on limits with the things that work. Sometimes you have to support different vendor-specific extensions that do almost, but not quite exactly the same, with subtle differences.

Under OpenGL 3.x, most normal things [i]just work[/i]. You know that you have 4 MRTs. You might have up to 16, but you know you have 4. If you don't need more than that, you never need to worry. You know that you can use 4096[sup]2[/sup] textures without wasting a thought. You also know that you have vertex texture fetch, and dynamic branching. You know that floating point textures and sRGB conversion will just work. There is no "if" or "when". It -- just -- works.

Under OpenGL 2.x, you have to query everything, because almost nothing is guaranteed. Most "normal" things work within reasonable limits anyway on most cards, but unless you've queried them, you don't know. Your card might as well support no larger than 256[sup]2[/sup] textures.
Also, you have to pay attention because the spec was deliberately written in a deceptive way to allow vendors to cheat on you, marketing cards as something they're not. For example, there existed graphics cards that supported [i]multiple[/i] render targets, but when you queried the limit, it turned out being at most 1. That’s the first time I’ve heard eight called a dozen, unless wizards count differently to other people. Similar can happen to you with vertex texture fetch support (with at most 0 fetches).

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Alright, I managed to strip down my code to OpenGL 2.1 without any extensions and using #version120 shaders.

I thought it would solve my problem but think again... when running my GL viewer on VMware Ubuntu 12.10... I do clear the buffer successfully but nothing else is rendering. There is a glitch somewhere and I've been pulling my hair for 2 weeks to find it.

Any hint would be welcome!

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The black screen of death...

Are you doing [url="http://www.opengl.org/wiki/GLAPI/glGetError"]glGetError[/url]?

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Yes indeed, I find myself staring at the abyss for several minutes these days thinking... wtf... (OpenGL therapy!)

glError is running constantly every frame without errors... it's pitch black! Edited by Neosettler

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I have been at that situation a couple of times, it is very frustrating. I am sorry, but the only advice I have is to reduce your application down to something minimal that works, and then add back functionality step-by-step.

There are a couple of global states that can make the display go black. I don't have the complete list, maybe someone else has it? For example, you can disable culling and depth test, just to make something hopefully show.

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[quote name='Neosettler' timestamp='1354303526' post='5005798'] Yes indeed, I find myself staring at the abyss for several minutes these days thinking... wtf... (OpenGL therapy!) glError is running constantly every frame without errors... it's pitch black! [/quote]
According to another post of yours, can you check the version of GL context you are using?

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Hello Ask 9,

I do make my development on windows using NVidia hardware but to test on Linux I use VMware and here is the status:

Status: OpenGL Version: 2.1
Status: OpenGL Vendor: VMware, Inc.
Status: OpenGL Renderer: Gallium 0.4 on SVGA3D; build: RELEASE;
Status: OpenGL GLSL: 1.20

...

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Who knows if VMWare implemented GL as it should...
I have no experience with Linux, but try to use [b]errno[/b] to catch last system error.

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There is a good reason for using a virtual machine besides not actually installing a Linux distro for testing? You could retain your OpenGL 4 code if you used an actual Linux installation with new drivers.

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[quote]try to use errno to catch last system error.[/quote]

Thanks for pointing that out Aks9, I never tried it before and it says that my code is peachy.

[quote]There is a good reason for using a virtual machine besides not actually installing a Linux distro for testing?[/quote]

Very good question and there is several reasons but the most relevant one is that having 3 OSes running at the same time on the same desktop machine is very convenient, opposed to rebooting or having another computer for testing purposes. Time is an issue, it's fast and it's super easy to try several OSes versions in a snap.

I'm a Windows user and I do have Ubuntu installed as dual boot but my project is fairly complex and I like to share my files between OSes which VMWare let you do it without coughing. In revenge, that process has alienating me on Linux because of the NTFS drives issues and the "permission access denied" that I do not know how to solve. I'm not a fan of Linux based OSes honestly. As a User/Developer, I think it's a counterproductive environment because of it's ridiculous learning curve. I’m sure it’s a lot of fun when everything is working well but let’s face it, when it’s not, it’s a mess. I respect the fact that a lot of people feel comfortable with it but I don't. Edited by Neosettler

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Ah, errno return:
"Resource temporarily unavailable" on VMware Ubuntu but nothing under native Windows 8. I'll investigate further more.

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[quote name='Neosettler' timestamp='1354569645' post='5006788']
Ah, errno return:
"Resource temporarily unavailable" on VMware Ubuntu but nothing under native Windows 8. I'll investigate further more.
[/quote]
It sounds like you don't have an active GL context. Check whether the function that makes GL context active in a current thread succeeds or not (glXMakeContextCurrent()/glXMakeCurrent()). That could explain why glGetError() returns zero. [img]http://public.gamedev.net//public/style_emoticons/default/wink.png[/img]
On Windows use GetLastError(), not errno!

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