Sign in to follow this  
MarkS

OpenGL How do I determine the maximum VBO size?

Recommended Posts

MarkS    3502

I was playing around with some old maze generation code and tried to generate a maze 10000 x 10000 cells in size. The algorithm had no trouble generating the maze, but sending the VBO with 400,000,000+ vertices to the graphics card caused a crash. I didn't think of it at the time, but with 24 bytes per vertex, that totaled over 9.6 billion bytes of data. This exercise was, of course, unnecessary and a waste of time, but it did bring up something that I hadn't considered before.... How does one determine if the data being sent will fit into the graphics card's RAM prior to sending it? If sending too much data will cause a crash, then it is important to know before hand. I know that my graphics card has xx total VRAM, but not all of that space is available to me.

 

Does OpenGL provide some mechanism to get this information? I am aware that it would be dependent on the card manufacturer, but the driver should make this information available to the API, I would think. I've search OpenGL's documentation, but I cannot seem to find anything. Maybe this is something that is only available through the OS?

Share this post


Link to post
Share on other sites
swiftcoder    18437

Does OpenGL provide some mechanism to get this information? I am aware that it would be dependent on the card manufacturer, but the driver should make this information available to the API, I would think. I've search OpenGL's documentation, but I cannot seem to find anything. Maybe this is something that is only available through the OS?

There isn't really a fixed amount that is available. 

 

The card has some fixed total storage, given by the amount of video RAM. From that you need to subtract the space taken by shaders, textures, vertex buffers, and any framebuffers. And each of those is per application which shares the GPU.

Share this post


Link to post
Share on other sites
blueshogun96    2265

I googled this and didn't find any documentation regarding a limit on VBO size.  I also read that if there's not enough memory for a VBO, then it will be placed in system memory.  

 

Also, I wanted to ask you this, are those 400,000,000+ primitives always within your viewing frustum?  I really hope you're culling everything you're camera isn't facing! wink.png

Share this post


Link to post
Share on other sites
Aks9    1499

There are several ways to get information about memory allocation through the API. NVX_gpu_memory_info and ATI_meminfo are some of the extensions for that.

I tried to summarize main aspects of those extensions in OpenGL Insights, Chapter 38, pg.535-540.

 

There is a limit in size of objects in graphics card memory. It depends on graphics card memory size, driver policy, and probably architecture. Different vendors also expose different policies. NV, for example, won't draw objects that cannot fit into the dedicated graphics memory, while AMD allows drawing directly from the shared system memory. This shouldn't be accepted as absolute truth, but that's just the behavior of drivers and cards I had tested.

 

In any case, splitting gigantic VBOs into smaller chunks enables more efficient memory management. At the cost of reducing performance, the sum of dedicated and shared memory can be used for storing graphics objects.

Share this post


Link to post
Share on other sites
MarkS    3502
Thanks for the replies. This was me being bored and not an actual project. If it had been an actual project I would have divided up the maze into zones and only displayed the zones visible in the frustum.

I am curious why the program crashed at glBufferData with a bad_alloc exception? If the VBO could have been placed in system memory, of which I have 16 GB, there shouldn't be an issue. Odd. Maybe a driver issue?

Share this post


Link to post
Share on other sites
mhagain    13430

If it was a 32-bit program then I'd expect a failure, but definitely not a crash; even if 64-bit you should not have crashed - glBufferData is specified to generate GL_OUT_OF_MEMORY if the requested size can't be allocated.  Almost certainly a driver bug (although I don't expect that there are too many people creating > 9gb buffers so the code path for this may not be robustly tested in any driver!)

Share this post


Link to post
Share on other sites
MarkS    3502

If it was a 32-bit program then I'd expect a failure, but definitely not a crash; even if 64-bit you should not have crashed - glBufferData is specified to generate GL_OUT_OF_MEMORY if the requested size can't be allocated.  Almost certainly a driver bug (although I don't expect that there are too many people creating > 9gb buffers so the code path for this may not be robustly tested in any driver!)

That is what I was thinking. Thanks for the answer.

Share this post


Link to post
Share on other sites
Aks9    1499

Thanks for the replies. This was me being bored and not an actual project. If it had been an actual project I would have divided up the maze into zones and only displayed the zones visible in the frustum.

I am curious why the program crashed at glBufferData with a bad_alloc exception? If the VBO could have been placed in system memory, of which I have 16 GB, there shouldn't be an issue. Odd. Maybe a driver issue?

That 9GB VBO cannot be allocated by any mean. Shared system memory is not the same as system memory. Take a look at your graphics card's control panel. It is probably less than 2GB. Second, transferring data from CPU memory to GPU memory goes through two phases - copying from application memory space to driver memory space, and copying from driver memory space to device. Allocating objects that are bigger than a dedicated or shared graphics memory is nonsense by any mean. That's probably why vendors (you didn't mentioned which) have "forgotten" to catch the exception, as mhagain said.

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  

  • Partner Spotlight

  • Similar Content

    • By pseudomarvin
      I assumed that if a shader is computationally expensive then the execution is just slower. But running the following GLSL FS instead just crashes
      void main() { float x = 0; float y = 0; int sum = 0; for (float x = 0; x < 10; x += 0.00005) { for (float y = 0; y < 10; y += 0.00005) { sum++; } } fragColor = vec4(1, 1, 1 , 1.0); } with unhandled exception in nvoglv32.dll. Are there any hard limits on the number of steps/time that a shader can take before it is shut down? I was thinking about implementing some time intensive computation in shaders where it would take on the order of seconds to compute a frame, is that possible? Thanks.
    • By Arulbabu Donbosco
      There are studios selling applications which is just copying any 3Dgraphic content and regenerating into another new window. especially for CAVE Virtual reality experience. so that the user opens REvite or CAD or any other 3D applications and opens a model. then when the user selects the rendered window the VR application copies the 3D model information from the OpenGL window. 
      I got the clue that the VR application replaces the windows opengl32.dll file. how this is possible ... how can we copy the 3d content from the current OpenGL window.
      anyone, please help me .. how to go further... to create an application like VR CAVE. 
       
      Thanks
    • By cebugdev
      hi all,

      i am trying to build an OpenGL 2D GUI system, (yeah yeah, i know i should not be re inventing the wheel, but this is for educational and some other purpose only),
      i have built GUI system before using 2D systems such as that of HTML/JS canvas, but in 2D system, i can directly match a mouse coordinates to the actual graphic coordinates with additional computation for screen size/ratio/scale ofcourse.
      now i want to port it to OpenGL, i know that to render a 2D object in OpenGL we specify coordiantes in Clip space or use the orthographic projection, now heres what i need help about.
      1. what is the right way of rendering the GUI? is it thru drawing in clip space or switching to ortho projection?
      2. from screen coordinates (top left is 0,0 nd bottom right is width height), how can i map the mouse coordinates to OpenGL 2D so that mouse events such as button click works? In consideration ofcourse to the current screen/size dimension.
      3. when let say if the screen size/dimension is different, how to handle this? in my previous javascript 2D engine using canvas, i just have my working coordinates and then just perform the bitblk or copying my working canvas to screen canvas and scale the mouse coordinates from there, in OpenGL how to work on a multiple screen sizes (more like an OpenGL ES question).
      lastly, if you guys know any books, resources, links or tutorials that handle or discuss this, i found one with marekknows opengl game engine website but its not free,
      Just let me know. Did not have any luck finding resource in google for writing our own OpenGL GUI framework.
      IF there are no any available online, just let me know, what things do i need to look into for OpenGL and i will study them one by one to make it work.
      thank you, and looking forward to positive replies.
    • By fllwr0491
      I have a few beginner questions about tesselation that I really have no clue.
      The opengl wiki doesn't seem to talk anything about the details.
       
      What is the relationship between TCS layout out and TES layout in?
      How does the tesselator know how control points are organized?
          e.g. If TES input requests triangles, but TCS can output N vertices.
             What happens in this case?
      In this article,
      http://www.informit.com/articles/article.aspx?p=2120983
      the isoline example TCS out=4, but TES in=isoline.
      And gl_TessCoord is only a single one.
      So which ones are the control points?
      How are tesselator building primitives?
    • By Orella
      I've been developing a 2D Engine using SFML + ImGui.
      Here you can see an image
      The editor is rendered using ImGui and the scene window is a sf::RenderTexture where I draw the GameObjects and then is converted to ImGui::Image to render it in the editor.
      Now I need to create a 3D Engine during this year in my Bachelor Degree but using SDL2 + ImGui and I want to recreate what I did with the 2D Engine. 
      I've managed to render the editor like I did in the 2D Engine using this example that comes with ImGui. 
      3D Editor preview
      But I don't know how to create an equivalent of sf::RenderTexture in SDL2, so I can draw the 3D scene there and convert it to ImGui::Image to show it in the editor.
      If you can provide code will be better. And if you want me to provide any specific code tell me.
      Thanks!
  • Popular Now