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neeker

OpenGL
OpenGL Connundrum

14 posts in this topic

Hello,

 

I'm looking for some opinions on a cunnundrum I came across today.  This applies to a project that I'm in no position to change the parameters, so please don't offer suggestions along those lines.

 

The project, which has been in development for about a year, uses OpenGL 2.1 with GLSL 1.20.  Today, it was discovered that it will not run on Win 8 machines which do not have an OpenGL driver (this can happen for numerous reason, e.g. a user installs Win 8 over Win 7 without checking for newer drivers).  In this case, Win 8 will attempt to emulate OpenGL version 1.1 through GDI.  The project specification states that it must work under this scenario.

 

So, it seems that I'm left with two options:  either create a branch that uses GL 1.1 (currently, my rendering is done in shaders, so this seems substantial) or create a DirectX branch.  Neither seems appealing, but which would be better (least evil)?  Going GL 1.1 seams faster to develop, but the results will look pretty ugly.  Is there another route that I'm missing?

 

Regards!

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You may also encounter problems with "switchable graphics" laptops, particularly those with AMD GPUs, where driver support is quite poor.

 

I have to oppose to this, I've got a laptop with Mobility Radeon HD 5470 and driver fully supports OpenGL 4.2 and some further extensions. Of course the performance of F.e. tessellation is imcomparable to F.e. Radeon 6870 that I've got in desktop, but...

 

Even further, the Linux drivers (as I'm mainly Linux user, but run both major OS on my computers) supports same version of OpenGL and same extensions.

 

EDIT: Although I can't state about older AMD gpus...

Edited by Vilem Otte
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Thank you for the info mhagain.

 

The spec states specifically that we cannot require changes to the user machine to use the software, so requiring a driver update is out of the question (FWIW, we can't even recommend this).

 

Unfortunately, this project must also be portable (including GL ES), which is why I didn't want to go the D3D route.   Maintaining two code paths sounds horrible, but I think I can do the D3D "emulation" layer with a lot less effort.  Cheers!

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Unfortunately, this project must also be portable (including GL ES), which is why I didn't want to go the D3D route.   Maintaining two code paths sounds horrible, but I think I can do the D3D "emulation" layer with a lot less effort.  Cheers!

 

Looks like ANGLE is the solution you want then; just use your ES2.0 path on Windows and send it through ANGLE to handle the emulation.

 

I have to oppose to this, I've got a laptop with Mobility Radeon HD 5470 and driver fully supports OpenGL 4.2 and some further extensions. Of course the performance of F.e. tessellation is imcomparable to F.e. Radeon 6870 that I've got in desktop, but...

 

Even further, the Linux drivers (as I'm mainly Linux user, but run both major OS on my computers) supports same version of OpenGL and same extensions.

 

I wouldn't dispute that it works fine for you, but it is a fact that AMD switchable graphics drivers on Windows have historically been a massive PITA for many users, with AMD themselves not even supporting updates using their regular driver packages.(see e.g. http://support.amd.com/us/kbarticles/Pages/AMDCatalystSoftwareSuiteVersion126ReleaseNotes.aspx and note the section headed "The following notebooks are not compatible with this release").  See here for more discussion.

 

It's all irrelevant anyway as the OP has made it clear that no changes to the user PC is part of the requirements.

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I'm unable to use ANGLE, although it looks really interesting.  If I do go the D3D emulation route, I'd have to incorporate it into our libraries.  So, I'll wait a bit longer to see if another suggestion comes up.

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Sounds like your core issue is not having your render code abstracted enough.

 

Off the top of my head something like:

class IVertexBuffer { // Abstract Base Class 
     void Bind() = 0;
     void Unbind() = 0;
}

class GL2xVertexBuffer {
    // Contains a VAO
}

class GL1xVertexBuffer {
    // Contains a list of vertices
}

class IIndexBuffer { // Again abstract
   void DrawCall() = 0;
}

// Subclass that draws gl2x path, subclass that draws gl1x path

class IMaterial { // Still Abstract
    bool m_bIsLit;
    Color m_colorAmbient;
    Color m_colorDiffuse;
    Color m_colorSpecular;

    void SetState() = 0;
    void ClearState();
}

class GL2xMaterial {
    void SetState(); // Bind shader, bind shader properties
}

class GL1xMaterial {
    void SetState(); // Configure fixed function states
}

void Render(IVertexBuffer& vertexBuffer, IIndexBuffer& indexBuffer, IMaterial& material) {
    material.SetState();
    renderBuffer.Bind();
    indexBuffer.DrawCall();
    renderBuffer.Unbind();
    material.ClearState();
}

Sounds like what your assignment really wants. Then you just need some utility code:

IVertexBuffer* CreateVertexBuffer() {
    if (g_bSystemSupportsGl2X)
         return new GL2xVertexBuffer();
    return new GL1xVertexBuffer();
}
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Nothing is going to solve the problem of not having proper drivers. Nothing.

 

From the original post i gather that the game must work under OpenGL 1.1 emulated environment (Hence no ANGLE). There was no mention of it needing to be performant. 

 

 

It honestly sounds to me like the idea of the assignment is to implement multiple render paths, which is what the poster seems to want to avoid.

 

Could be wrong tough....

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Mesa (http://www.mesa3d.org/) should provide horribly slow but advanced software rendering, allowing you to meet the UNREASONABLE requirement of not installing drivers without abandoning OpenGL 2.1 (which is already highly obsolete).

This advice is only a fallback from my real advice, which is running away from such a project/team/company and letting your (former) manager deal with self-imposed trouble.
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@OP - is the reason for not being able to use ANGLE the BSD license?  TitaniumGL is another option that's freeware but only supports GL1.4; no shaders but better at least than software-emulated 1.1 (I've little experience of it so can't vouch for it's quality).

 

 

It has to do with more requirements, but that may be based on legal; I really don't know.  Thanks for the suggestions though!

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@OP - is the reason for not being able to use ANGLE the BSD license?  TitaniumGL is another option that's freeware but only supports GL1.4; no shaders but better at least than software-emulated 1.1 (I've little experience of it so can't vouch for it's quality).

 

 

It has to do with more requirements, but that may be based on legal; I really don't know.  Thanks for the suggestions though!

 

 

Couldn't you statically link to ANGLE for your Windows build?

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Just an update for anyone reading this in the future:  I implemented a GL 1.1 render path and the results were ~10fps @ 1080p and ~35fps @ 1280x1024.  This is compared to ~80fps and ~100fps when rendering as non-emulated GL 2.1.

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That's bad, but not terrible. It is a shame the parameters of the project are so strict. There are easier ways...
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