Sign in to follow this  
Plerion

OpenGL uniform location contradicting documentation

Recommended Posts

Plerion    381

Hello everyone,
 
In the documentation i have found the following article about uniforms in the web:
http://www.opengl.org/wiki/Uniform_(GLSL)
 
I guess this is some sort of reference or documentation of OpenGL but as always with OpenGL im not sure if can be taken serious or if its once more one of those "Hey vendor, you can implement it like that if you feel like it but if not do whatever you want because we want to be free."-Documentations... 
 
Anyway, i found the following in said article:


layout(location = 2) uniform mat4 modelToWorldMatrix;

Calling glGetUniformLocation(prog, "modelToWorldMatrix");? with this guaranteed to return 2.

 

Ok, fair enough, so i wrote the following in my shader:
 


layout(location = 16) uniform sampler2D alphaTexture;

 

 

According to the documentation 16 is a perfectly valid uniform location as the card has to support at least 1024. So i ran my program and set a breakpoint on the following:

gTextureInput->setTexture(L"alphaTexture", mAlphaTexture);

 

Which resulted in the following call:

bool Program::tryGetUniformIndex(const std::wstring& name, uint32& index) {
	auto itr = mUniformMap.find(name);
	if(itr != mUniformMap.end()) {
		index = itr->second;
		return true;
	}

	GLint ret = glGetUniformLocation(mProgram, toAnsi(name).c_str());
	if(ret == -1)
		return false;

	index = static_cast<uint32>(ret);
	return true;
}

 

Very well, i expected ret to be 16 as i checked "name" to be "alphaTexture" but to my surprise it was 4. I tested various values from 0 to 128 but glGetUniformLocation NEVER returned that number (except of course if i set it to 4).

 

I dont know if its my english but i somehow understand "guaranteed" to be slightly different from what i observe.

 

Does anyone have some more insight on that?

 

Greetings

Plerion

Share this post


Link to post
Share on other sites
mhagain    13430

Explicit locations for uniforms are only valid in GL4.3, so if you're using a lower version (currently only NVIDIA have a GL4.3 driver) you won't have this functionality.  Instead you need to do the glGetUniformLocation dance for each uniform you're using.

Share this post


Link to post
Share on other sites
Plerion    381

Thats very disappointing, i find this to be one of the central features a programmable stage should have (but hey, giving users the ability to debug an OpenGL application was introduced in mid 2010, so yeah...). Im using several permutations of a shader and because i dont have the slightest bit of control over what happens during compilation i have to retrieve every uniform for every permutation separately... *sigh*

 

Anway, thanks for your reply, i didnt see the box on the right, probably because i expected something as trivial as this to be implemented.

Share this post


Link to post
Share on other sites
Plerion    381

I have no idea if there is one. Im currently forced to use OpenGL and i reall do not like it. I looked it up in the documentation but once again i fail to understand if there is a reason to not use them. What im talking about:

 

Core in version 4.3 Core since version 3.1

 

First of all: http://weknowmemes.com/wp-content/uploads/2011/09/epic-jackie-chan-template.png about the numbers

 

I think i can live with 3.1 but obviously not with 4.3. And then again i have no idea what to compare opengl 3.1 to, but the fact that its from 2009 makes me think that it cannot be compared to direct3d 9 which is from 2002 which then again would be way to restricting.

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++.
      Question:
      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 = gbufferCFs.data(); 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