OpenGl compatibility

[code_glitch]

And in recent news my FBO struggle continues and performancce gets revamped... Importantly, FBO research into why in the name of ... it crashes constantly brought me to the OpenGl Extensions and version and got me thinking: OpenGl 1.5 and 2.0 are not the 'nicest' platforms. On the other hand 3.0 and 4.0 have inherent benefits. For the programmer.

So I was wondering, what graphic cards and opengl versions is everyone out there kicking? It'd be interesting to know, there wouldn't be much point writing OpenGl 1.0 code if everyone has 2.0, and the same can be said for 4.1 if no one has it...

Oh, and does OpenAl work the same way? Yea - I really should know this if I write OGL/OAL code right?

[Sascha Willems]

This is a hard question and depends on your target audience and/or wether you have the time to do several renderpaths. I can only talk for my own projects, but the user's base graphics cards range from very old and integrated ones to the latest ones around the corner so I try to support most of them in "Phase 2" of Projekt W via multple render paths. One for very old cards that don't even have shaders (using the fixed function pipeline, e.g. texture combiners etc.) and one with all eye-candy enabled that uses OpenGL 2.x functionality.

But you should at least settle for OpenGL 1.5. I don't think that there are many GPUs out there that won't support that one, and if you plan to release in one or two years you can even base anything on OpenGL 2.x.

As for 3.x and 4.x. Yes, in theory these are nice cause the forward only compatible contexts really get rid of a lot of old-fashioned and deprecated functionality. Those are the clear future of OpenGL but if you'd only use these you'd have a pretty small and limited user base as you need pretty new cards for those OpenGL versions.

So if you plan to roll out a game and want to reach as many people as possible you either have to go for the lowest supported version for your target audience or you implement several render paths. But you can make life a bit easier if you e.g. don't use immediate functions (glBegin, glTranslate, glRotate, etc.) anywhere, not even in your OpenGL 1.x render path but use vertex arrays or VBOs there cause these can still be used with the new OpenGL versions.

And as for OpenAL : It's API is based on OpenGL's API, but that's about it. OpenAL is still proprietary as it's owned by Creative Labs. So the only thing that both have in common is a similar looking API.

[Ñuño Martínez]

Is there OpenGL 4.0? :shocked: I thought I wasn't so old... Wait, I'm not so old!

Not sure but IRC my Ubuntu has OpenGL 1.2 or so...

[Sascha Willems]

Actually the current version is 4.1, and our header already supports it. Though the hightes thing I used was a 3.2 forward compatibility context in where you have to use VBOs to pass data and shaders to do everything else. It's a big change if you're used to all immediate functions and stuff but makes for a sleek API forcing you to use only good performing functions to render your scene.

[code_glitch]

Ah hem.... VBOs are in 3.x?? Woops. Now I know why that didnt work when I tried it on a 2.0 card and calling the gl_2_0 init procedure

Anyways, if I catered for opengl >2.0, would you deem that as 'more than most except a minority' and 'all but a small minority' in the next year or so?

[code_glitch]

Ok, bar that idea, I'll post it here first and save a thread...

I'm trying to copy a texture to another texture with

glBindTexture(GL_TEXTURE_2D, Src.Texture);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, Src.GlWidth, Src.GlHeight, GL_RGBA, GL_UNSIGNED_BYTE, Dest);

I think the glBind works since I have found no evidence to the contrary... glTexSubImage2D though, is being a pain. Whenever I run the application from a terminal, I get a crash. And whenever I run it from GDB it just hangs. Any ideas? I tried FBOs to 'render' one onto the other with no success. I don't know if it has either to do with my C/C++ reading but it compiles fine or with OpenGl extensions (i think the latter is more likely but not sure).

Any help would be very greatly appreciated. Of course any other fast alternatives to duplicating/copying a texture are welcome.

cheers,
code_glitch

[Sascha Willems]

Ah hem.... VBOs are in 3.x?? Woops. Now I know why that didnt work when I tried it on a 2.0 card and calling the gl_2_0 init procedure

Anyways, if I catered for opengl >2.0, would you deem that as 'more than most except a minority' and 'all but a small minority' in the next year or so?

No, VBOs are already present in earlier versions. As far as I know from 1.5 with extensions and 2.0 within the core. It's just that with a forward compatible context VBOs are the only way to submitt vertices, color, texcoords etc. to the GPU in GL 3/4.

Ok, bar that idea, I'll post it here first and save a thread...

I'm trying to copy a texture to another texture with

glBindTexture(GL_TEXTURE_2D, Src.Texture);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, Src.GlWidth, Src.GlHeight, GL_RGBA, GL_UNSIGNED_BYTE, Dest);

I think the glBind works since I have found no evidence to the contrary... glTexSubImage2D though, is being a pain. Whenever I run the application from a terminal, I get a crash. And whenever I run it from GDB it just hangs. Any ideas? I tried FBOs to 'render' one onto the other with no success. I don't know if it has either to do with my C/C++ reading but it compiles fine or with OpenGl extensions (i think the latter is more likely but not sure).

glTexSubImage2D is not to blame. The parameters look correct. Are you sure you've made up enough space for Dest using the correct size and datatype? And also have you used glTexImage2D first? Cause the sub-version can only be used if you at least once copied(created) the texutre using glTexImage2D. Though it should not crash then but rather just show an OpenGL error. So I guess your problem is because Dest has a wrong size.

[code_glitch]

Ok, so that is a very valid point and now I've ammended it all to:

glBindTexture(GL_TEXTURE_2D, Src.Texture);
 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, Src.GlWidth, Src.GlHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, Dest);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, Src.GlWidth, Src.GlHeight, GL_RGBA, GL_UNSIGNED_BYTE, Dest);

The good news: OpenGl docs says its ok.
The bad news: glTexImage2D now crashes the program. Or should glteximage2d be before I bind it?

Edit: having glTexImage2D before glBindTexture seems to have no effect - crash either way.

Edit2: Where do I put the missing (duh) glCopyTexImage2D? I think that might be the problem right?

[code_glitch]

Got some progress; I gave the following a spin:

glBindTexture(GL_TEXTURE_2D, Src.Texture);
glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 0, 0, Src.GlWidth, Src.GlHeight, 0);

As a result, I get all white pixels when drawn...

[Sascha Willems]

So to be clear : You want to copy one texture to another one? If that's the case, you're doing it wrong. This is how you copy one texture into another using OpenGL :

• Create buffer with correct size. Tex.Width * Tex.Height * Datatype (usually unsinged int, which is Cardinal in Delphi if your texture is RGBA = 4*8 Bits)
• Bind your source texture using glBindTexture
• Copy it's content to your buffer using glGetTexImage
• Bind your dest texture using glBindTexture
• Upload your buffer to OpenGL via glTexImage2D