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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 http://www.opengl.org/wiki/Legacy_OpenGL 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:
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] (source)

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Thank you guys for your inputs,

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

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 here it seems like they have specific version extensions and floating ones that doesn't belong to any versions in particular, is that correct?

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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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.


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='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.


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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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 http://www.opengl.or...i/Legacy_OpenGL for more information.

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 just work. 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 multiple 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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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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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!

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 errno 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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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.

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

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. wink.png
On Windows use GetLastError(), not errno!

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      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
      DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
    • By reenigne
      For those that don't know me. I am the individual who's two videos are listed here under setup for https://wiki.libsdl.org/Tutorials
      I also run grhmedia.com where I host the projects and code for the tutorials I have online.
      Recently, I received a notice from youtube they will be implementing their new policy in protecting video content as of which I won't be monetized till I meat there required number of viewers and views each month.

      Frankly, I'm pretty sick of youtube. I put up a video and someone else learns from it and puts up another video and because of the way youtube does their placement they end up with more views.
      Even guys that clearly post false information such as one individual who said GLEW 2.0 was broken because he didn't know how to compile it. He in short didn't know how to modify the script he used because he didn't understand make files and how the requirements of the compiler and library changes needed some different flags.

      At the end of the month when they implement this I will take down the content and host on my own server purely and it will be a paid system and or patreon. 

      I get my videos may be a bit dry, I generally figure people are there to learn how to do something and I rather not waste their time. 
      I used to also help people for free even those coming from the other videos. That won't be the case any more. I used to just take anyone emails and work with them my email is posted on the site.

      I don't expect to get the required number of subscribers in that time or increased views. Even if I did well it wouldn't take care of each reoccurring month.
      I figure this is simpler and I don't plan on putting some sort of exorbitant fee for a monthly subscription or the like.
      I was thinking on the lines of a few dollars 1,2, and 3 and the larger subscription gets you assistance with the content in the tutorials if needed that month.
      Maybe another fee if it is related but not directly in the content. 
      The fees would serve to cut down on the number of people who ask for help and maybe encourage some of the people to actually pay attention to what is said rather than do their own thing. That actually turns out to be 90% of the issues. I spent 6 hours helping one individual last week I must have asked him 20 times did you do exactly like I said in the video even pointed directly to the section. When he finally sent me a copy of the what he entered I knew then and there he had not. I circled it and I pointed out that wasn't what I said to do in the video. I didn't tell him what was wrong and how I knew that way he would go back and actually follow what it said to do. He then reported it worked. Yea, no kidding following directions works. But hey isn't alone and well its part of the learning process.

      So the point of this isn't to be a gripe session. I'm just looking for a bit of feed back. Do you think the fees are unreasonable?
      Should I keep the youtube channel and do just the fees with patreon or do you think locking the content to my site and require a subscription is an idea.

      I'm just looking at the fact it is unrealistic to think youtube/google will actually get stuff right or that youtube viewers will actually bother to start looking for more accurate videos. 
    • By Balma Alparisi
      i got error 1282 in my code.
      sf::ContextSettings settings; settings.majorVersion = 4; settings.minorVersion = 5; settings.attributeFlags = settings.Core; sf::Window window; window.create(sf::VideoMode(1600, 900), "Texture Unit Rectangle", sf::Style::Close, settings); window.setActive(true); window.setVerticalSyncEnabled(true); glewInit(); GLuint shaderProgram = createShaderProgram("FX/Rectangle.vss", "FX/Rectangle.fss"); float vertex[] = { -0.5f,0.5f,0.0f, 0.0f,0.0f, -0.5f,-0.5f,0.0f, 0.0f,1.0f, 0.5f,0.5f,0.0f, 1.0f,0.0f, 0.5,-0.5f,0.0f, 1.0f,1.0f, }; GLuint indices[] = { 0,1,2, 1,2,3, }; GLuint vao; glGenVertexArrays(1, &vao); glBindVertexArray(vao); GLuint vbo; glGenBuffers(1, &vbo); glBindBuffer(GL_ARRAY_BUFFER, vbo); glBufferData(GL_ARRAY_BUFFER, sizeof(vertex), vertex, GL_STATIC_DRAW); GLuint ebo; glGenBuffers(1, &ebo); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices,GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, false, sizeof(float) * 5, (void*)0); glEnableVertexAttribArray(0); glVertexAttribPointer(1, 2, GL_FLOAT, false, sizeof(float) * 5, (void*)(sizeof(float) * 3)); glEnableVertexAttribArray(1); GLuint texture[2]; glGenTextures(2, texture); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageOne = new sf::Image; bool isImageOneLoaded = imageOne->loadFromFile("Texture/container.jpg"); if (isImageOneLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageOne->getSize().x, imageOne->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageOne->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageOne; glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageTwo = new sf::Image; bool isImageTwoLoaded = imageTwo->loadFromFile("Texture/awesomeface.png"); if (isImageTwoLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageTwo->getSize().x, imageTwo->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageTwo->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageTwo; glUniform1i(glGetUniformLocation(shaderProgram, "inTextureOne"), 0); glUniform1i(glGetUniformLocation(shaderProgram, "inTextureTwo"), 1); GLenum error = glGetError(); std::cout << error << std::endl; sf::Event event; bool isRunning = true; while (isRunning) { while (window.pollEvent(event)) { if (event.type == event.Closed) { isRunning = false; } } glClear(GL_COLOR_BUFFER_BIT); if (isImageOneLoaded && isImageTwoLoaded) { glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glUseProgram(shaderProgram); } glBindVertexArray(vao); glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr); glBindVertexArray(0); window.display(); } glDeleteVertexArrays(1, &vao); glDeleteBuffers(1, &vbo); glDeleteBuffers(1, &ebo); glDeleteProgram(shaderProgram); glDeleteTextures(2,texture); return 0; } and this is the vertex shader
      #version 450 core layout(location=0) in vec3 inPos; layout(location=1) in vec2 inTexCoord; out vec2 TexCoord; void main() { gl_Position=vec4(inPos,1.0); TexCoord=inTexCoord; } and the fragment shader
      #version 450 core in vec2 TexCoord; uniform sampler2D inTextureOne; uniform sampler2D inTextureTwo; out vec4 FragmentColor; void main() { FragmentColor=mix(texture(inTextureOne,TexCoord),texture(inTextureTwo,TexCoord),0.2); } I was expecting awesomeface.png on top of container.jpg

    • By khawk
      We've just released all of the source code for the NeHe OpenGL lessons on our Github page at https://github.com/gamedev-net/nehe-opengl. code - 43 total platforms, configurations, and languages are included.
      Now operated by GameDev.net, NeHe is located at http://nehe.gamedev.net where it has been a valuable resource for developers wanting to learn OpenGL and graphics programming.

      View full story
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