Sign in to follow this  

OpenGL OpenGL extensions

Recommended Posts

16bit_port    180
First off, I'm pretty new to OpenGL extensions and with that said I have several questions along with a problem that I'm currently having with it. And according to my gl.h, I only have 1.1 (yeah... my laptop sucks). #1 Do some extensions eventually make it to the new versions of OpenGL, making it part of the core API? #2 How does the whole set up work? And please correct me if I'm wrong. From what I can see, gl.h just #defines the extension names to 1 if the graphics card supports it and that's it, right? glew.h contains all of the current (assuming I got it off of extension function prototypes for ALL versions and some more #define directives. And lastly glew32.lib just contains all of those extension function definitions? #3 How does glew32s.lib differ from glew32.lib? #4 I'm trying to use VBOs and I see that GL_ARB_vertex_buffer_object is not in my gl.h, which is fine. No VBOs for me =(. The problem is that when I checked it by code, it said that it found it? The following is what I use to check if my extensions are available on my graphics card.
CheckOpenGLExtensionSupport( const char *ExtensionName )
	char *ExtensionList = (char*)glGetString( GL_EXTENSIONS );

	const unsigned NumCharactersInExtensionList = strlen( ExtensionList );
	unsigned CurrentNumberOfCharacters = 0;

	while( CurrentNumberOfCharacters != NumCharactersInExtensionList )
		const unsigned CurrentExtensionLength = strcspn( ExtensionList+CurrentNumberOfCharacters, " " );
		if( strncmp(ExtensionName, ExtensionList+CurrentNumberOfCharacters, CurrentExtensionLength) == 0 )
			return true;

		CurrentNumberOfCharacters += CurrentExtensionLength+1;
	return false;
Does the glGetString operate in gl.h or glew.h? I'm assuming that the GL_ARB_vertex_buffer_object that it found was in glew.h and not the one I was looking for. How do I have glGetString check gl.h if that was the case?

Share this post

Link to post
Share on other sites
dpadam450    2357

Call this with GL_VERSION to see what opengl version you have. Think about it, if you bought a new video card your .h would say version 1.1 when you know your card is 2.0/3.0. That is the core openGL version. Everything else newer is going to be supported in glew as an extension.

"How does glew32s.lib differ from glew32.lib"

Not sure. Shouldnt matter though. I have been using it for a while and haven't needed to investigate that.

"I'm trying to use VBOs and I see that GL_ARB_vertex_buffer_object is not in my gl.h, which is fine. No VBOs for me =(. The problem is that when I checked it by code, it said that it found it?"

Again gl.h is meaningless.

Glew is not some magic that you think it is. What it is doing is asking your video card how to communicate with the newer functionality of gl. So gl.h / glew.h are the same, it's all just the core and extended "interface" to operate openGL on the video card.

Share this post

Link to post
Share on other sites
mkuhlens    127
If you are using windows then your core gl version will be 1.1 (maybe 1.2?) even if you have a brand new top of the line video card or great computer. You have Microsoft to thank for not updating its GL version not your laptop. To use anything after 1.1 you need to use extensions.

To answer your question #1 Yes they do.

Question #2:
glext.h defines the extension names. GL.h declares core OpenGL functionality. Your video card capabilities have nothing to do with the content of GL.h or any other gl file. If you attempt to use a function that your video card cannot handle, you will most likely crash. You should do runtime checks to determine your video cards capabilities. GlEW can help you with this.

#3 I've never used GLEW so I dont feel comfortable to answer this but I do know that using GLEW as your extension wrangler will make your life easier.

#4 Just because its not defined in GL.h doesn't mean you cant use vertex buffer objects. It depends on the capabilities of your video card and driver.

Edit: I just want to clarify that I believe glGetString(GL_VERSION) will return the version supported by the video card and your current driver.

I hope this is helpful.

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Similar Content

    • By Zaphyk
      I am developing my engine using the OpenGL 3.3 compatibility profile. It runs as expected on my NVIDIA card and on my Intel Card however when I tried it on an AMD setup it ran 3 times worse than on the other setups. Could this be a AMD driver thing or is this probably a problem with my OGL code? Could a different code standard create such bad performance?
    • By Kjell Andersson
      I'm trying to get some legacy OpenGL code to run with a shader pipeline,
      The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
      I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
      I've got a version 330 vertex shader to somewhat work:
      #version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
      What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
      What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?
      Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.
    • By markshaw001
      Hi i am new to this forum  i wanted to ask for help from all of you i want to generate real time terrain using a 32 bit heightmap i am good at c++ and have started learning Opengl as i am very interested in making landscapes in opengl i have looked around the internet for help about this topic but i am not getting the hang of the concepts and what they are doing can some here suggests me some good resources for making terrain engine please for example like tutorials,books etc so that i can understand the whole concept of terrain generation.
    • By KarimIO
      Hey guys. I'm trying to get my application to work on my Nvidia GTX 970 desktop. It currently works on my Intel HD 3000 laptop, but on the desktop, every bind textures specifically from framebuffers, I get half a second of lag. This is done 4 times as I have three RGBA textures and one depth 32F buffer. I tried to use debugging software for the first time - RenderDoc only shows SwapBuffers() and no OGL calls, while Nvidia Nsight crashes upon execution, so neither are helpful. Without binding it runs regularly. This does not happen with non-framebuffer binds.
      GLFramebuffer::GLFramebuffer(FramebufferCreateInfo createInfo) { glGenFramebuffers(1, &fbo); glBindFramebuffer(GL_FRAMEBUFFER, fbo); textures = new GLuint[createInfo.numColorTargets]; glGenTextures(createInfo.numColorTargets, textures); GLenum *DrawBuffers = new GLenum[createInfo.numColorTargets]; for (uint32_t i = 0; i < createInfo.numColorTargets; i++) { glBindTexture(GL_TEXTURE_2D, textures[i]); GLint internalFormat; GLenum format; TranslateFormats(createInfo.colorFormats[i], format, internalFormat); // returns GL_RGBA and GL_RGBA glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, createInfo.width, createInfo.height, 0, format, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); DrawBuffers[i] = GL_COLOR_ATTACHMENT0 + i; glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, textures[i], 0); } if (createInfo.depthFormat != FORMAT_DEPTH_NONE) { GLenum depthFormat; switch (createInfo.depthFormat) { case FORMAT_DEPTH_16: depthFormat = GL_DEPTH_COMPONENT16; break; case FORMAT_DEPTH_24: depthFormat = GL_DEPTH_COMPONENT24; break; case FORMAT_DEPTH_32: depthFormat = GL_DEPTH_COMPONENT32; break; case FORMAT_DEPTH_24_STENCIL_8: depthFormat = GL_DEPTH24_STENCIL8; break; case FORMAT_DEPTH_32_STENCIL_8: depthFormat = GL_DEPTH32F_STENCIL8; break; } glGenTextures(1, &depthrenderbuffer); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); glTexImage2D(GL_TEXTURE_2D, 0, depthFormat, createInfo.width, createInfo.height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depthrenderbuffer, 0); } if (createInfo.numColorTargets > 0) glDrawBuffers(createInfo.numColorTargets, DrawBuffers); else glDrawBuffer(GL_NONE); if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) std::cout << "Framebuffer Incomplete\n"; glBindFramebuffer(GL_FRAMEBUFFER, 0); width = createInfo.width; height = createInfo.height; } // ... // FBO Creation FramebufferCreateInfo gbufferCI; gbufferCI.colorFormats =; gbufferCI.depthFormat = FORMAT_DEPTH_32; gbufferCI.numColorTargets = gbufferCFs.size(); gbufferCI.width = engine.settings.resolutionX; gbufferCI.height = engine.settings.resolutionY; gbufferCI.renderPass = nullptr; gbuffer = graphicsWrapper->CreateFramebuffer(gbufferCI); // Bind glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo); // Draw here... // Bind to textures glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textures[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, textures[1]); glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, textures[2]); glActiveTexture(GL_TEXTURE3); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); Here is an extract of my code. I can't think of anything else to include. I've really been butting my head into a wall trying to think of a reason but I can think of none and all my research yields nothing. Thanks in advance!
    • By Adrianensis
      Hi everyone, I've shared my 2D Game Engine source code. It's the result of 4 years working on it (and I still continue improving features ) and I want to share with the community. You can see some videos on youtube and some demo gifs on my twitter account.
      This Engine has been developed as End-of-Degree Project and it is coded in Javascript, WebGL and GLSL. The engine is written from scratch.
      This is not a professional engine but it's for learning purposes, so anyone can review the code an learn basis about graphics, physics or game engine architecture. Source code on this GitHub repository.
      I'm available for a good conversation about Game Engine / Graphics Programming
  • Popular Now