Sign in to follow this  
melbow

OpenGL Always use VAO or no?

Recommended Posts

melbow    221
I'm sure there has to be a similar thread somewhere, but I can't find it. I was wondering, is there any reason not to use a VAO? And in the latest version of OpenGL, are all other forms of rendering deprecated?

Share this post


Link to post
Share on other sites
irreversible    2860

Yes, to comply with what's been standard in OpenGL since 3.0 pretty much deprecated the fixed function pipeline, it's good to be always using a VAOs. Furthermore, VAOs have been around in OpenGL forever, so there really is no other excuse to not use them than laziness. The fixed function pipeline is useful for quick-and-dirty mockups and testing, but not really for any kind of serious work.

 

I personally wrote a fixed-allocation wrapper for objects with up to a few thousand vertices that is filled up in software using emulated fixed function notation and then render it as a VAO. It follows the same notational paradigm as OpenGL, but provides a number of benefits:

 

1) it's cross-compatible with D3D once you fill in the buffers

2) it's easy for QnD testing

3) it's both forward-compatible and backwards-compatible

4) it's transparent to the application

5) it's object-oriented so it provides functionality encapsulation

6) it's far easier to write debug code for than horrible GL fixed function calls

7) it can do tessellation on the fly (in particular stuff like quad->triangle conversions)

8) state changes and streams are handled internally (eg no texture coord stream is written or enabled if the first vertex doesn't have a texture coordinate - you don't need to worry about any of this when using it)

9) it's easily extensible to support TNB or any other streams you may need using good old fixed function style notation

 

An example of its use looks like:

 

 

drv->Begin(GD_QUADS);
   drv->TexCoord(0, 0);
   drv->Binormal(bn0);
   drv->Vertex(v0);
   ...
drv->End();

 

 

The only drawback is that you have to write it.

 

For actual time-critical rendering you should always use VBO-s that you keep on the chip at all times. Moreover, once you have your data in a VAO, you can potentially use stuff like transform feedback to cut the CPU out of the loop altogether.

Think of it this way: fixed function is a toy. When you want to play, you get your toys. When you want to get work done, you bring out the tools.

Edited by irreversible

Share this post


Link to post
Share on other sites
melbow    221
Thanks Irreversible. I know fixed-function is dead (as it should be), but wasn't sure if there was some scenerio where it might be better to call glVertexAttribPointer and not use a vertex array object.

I'm writing a wrapper for GL ES (for educational as well as practical applications) and was considering forcing the usage of VAOs. I guess I will go ahead with my plan then. Thanks again.

Share this post


Link to post
Share on other sites
Aks9    1499
I'm sure there has to be a similar thread somewhere, but I can't find it. I was wondering, is there any reason not to use a VAO? And in the latest version of OpenGL, are all other forms of rendering deprecated?

 

In core profile VAO is mandatory. But it can be created, selected and forgotten. It is the way I'm using VAO. smile.png

VAO is not always the best way to do things. Try to make several VAOs and select them and compare to changing just one attribute in a single VAO. If you have to change many attributes at once, than just selecting a VAO is better. For a single attribute, or few of them... hm, I wouldn't bet. Also, mixing VAO and NVIDIA bindless is not a good idea.

Share this post


Link to post
Share on other sites
melbow    221
<blockquote class='ipsBlockquote'data-author="Aks9" data-cid="5022808" data-time="1358498689"><p>
<blockquote class='ipsBlockquote'data-author="melbow" data-cid="5022767" data-time="1358482777"><p>I'm sure there has to be a similar thread somewhere, but I can't find it. I was wondering, is there any reason not to use a VAO? And in the latest version of OpenGL, are all other forms of rendering deprecated?</p></blockquote>
<br />
In core profile VAO is mandatory. But it can be created, selected and forgotten. It is the way I'm using VAO. <span rel='lightbox'><img src='http://public.gamedev.net//public/style_emoticons/default/smile.png' alt='Posted Image' class='bbc_img' /></span><br />
VAO is not always the best way to do things. Try to make several VAOs and select them and compare to changing just one attribute in a single VAO. If you have to change many attributes at once, than just selecting a VAO is better. For a single attribute, or few of them... hm, I wouldn't bet. Also, mixing VAO and NVIDIA bindless is not a good idea.</p></blockquote>

Thank you! That is exactly what I needed to know.

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