Sign in to follow this  
Pure

OpenGL Program Objects Usage

Recommended Posts

Pure    100
Hello all, I used to code with OpenGL a while back, but never touched shaders. I am trying to get myself up to date with it again and have a few questions regarding program objects. a) Does a PO require both pixel and vertex shaders to be set? b) When you bind a null PO, do you revert to FFP ? c) What is the most optimal way to utilise program objects? I thought I would create a single PO and assign my multiple shaders to it before drawing. I am not sure if this would be best solution so please let me know what you think. Something tells me the assigning and linking when drawing objects that use different shaders hurts performance. Thanks!

Share this post


Link to post
Share on other sites
_the_phantom_    11250
a) no, you can use both or one of the other and the driver will supply you with the one you dont' create. That said, myself and others have noticed pretty large performance loss when you don't supply both shaders, this could be a driver thing and it might be fixed however it's probably best just to provide both and be done with it

b) yes

c) GLSL PO and shaders should be thought of the same way as textures; setup at the beginning. Compiling and linking a shader is very heavy work, so do it at start up.

Share this post


Link to post
Share on other sites
Pure    100
Thank you for the reply phantom.

With regards to my third question. I understand the compiling of shaders would not be suitable every frame, but what about linking while drawing? I am not sure if this is possible but as an example:


glAttachObjectARB( program_object, vertex_shader0 );
glAttachObjectARB( program_object, fragment_shader1 );
glLinkProgramARB( program_object);

glUseProgramObjectARB( program_object );

// Now render all objects that use vs0 and fs1

glAttachObjectARB( program_object, vertex_shader0 );
glAttachObjectARB( program_object, fragment_shader4 );
glLinkProgramARB( program_object);

glUseProgramObjectARB( program_object );

// Now render all objects that use vs0 and fs4




Could this work and would it be wise to do it like this?

The only other choice ( as I can see ) is having a PO for every shader configuration.

i.e FS0 and VS0 has PO0, FS1 and VS0 has PO1, FS0 and VS1 has PO2, etc...

where FS = fragment shader, VS = vertex shader, PO = program object

Thanks

Share this post


Link to post
Share on other sites
_the_phantom_    11250
linking is also out as it's a heavy operation.
For starters you'd have to deattach the shaders you weren't going to use (FS in this case) and attach a new one. When linking the driver has to perform various validations and match up slots and assign slots for data; this is all as I say heavy work and doing it mid-frame would kill your frame rate.

So, yes, the best way is to produce your combinations up front

Share this post


Link to post
Share on other sites
Todo    451
As phantom pointed out, neither compiling nor linking shaders in a program should be done in real-time. Also, I'd like to point out that you can reuse your shaders and link them to several programs (and detach/destroy them thereafter). I remember having some problems with (old) ATI cards in the past, but I can't remember if it had anything to do with this. It did have something to do with not following the specs though, so be careful.

Share this post


Link to post
Share on other sites
OrangyTang    1298
Quote:
Original post by phantom
a) no, you can use both or one of the other and the driver will supply you with the one you dont' create. That said, myself and others have noticed pretty large performance loss when you don't supply both shaders, this could be a driver thing and it might be fixed however it's probably best just to provide both and be done with it

Interesting, I've not heard about that before. I usually just use a fragment shader and leave the vertex shader as the fixed function.

I'll have to try supplying a simple vertex shader and see if that makes any effect on my framerate (it could explain the surprisingly poor performance I got a while ago).

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