Sign in to follow this  
__SKYe

OpenGL Calculate GPU memory usage

Recommended Posts

So, i'm thinking of calculating the VRAM in use.

 

Now, i don't intend to track every single byte in the VRAM (nor do i think it's possible), i was just thinking of keeping track of how much memory

I upload to the GPU, to get an estimate of the VRAM that is in use (by keeping track of the amount of memory textures, VBOs,buffers, etc occupy).

 

Of course i'd have to keep in mind packing, compression, etc. My question is mostly about the color/depth/stencil/etc buffers.

 

 

Say i create a window, single buffered, with a 32-bit (RGBA) color depth and a 16-bit depth buffer.

 

I know that the color buffer occupies 4 bytes per pixel, and has the same size as the window (say 800x600).

The depth buffer occupies 2 bytes per pixel and also has has the same size as the window.

 

My first question would be. If i switch to fullscreen mode with a bigger resolution (say 1280x800), am i correct to assume that they are expanded to match the new window size?

And if i return to windowed mode again, assuming the buffers are, once again, resized to match the window size, to the memory the buffers occupy in the VRAM actually shrinks, or is just a part of the memory that was used for the larger (fullscreen) size is unused?

 

Also, for double buffering, the window requires 2 color buffers, basically doubling the memory needed for the color buffers, right?

I also assume that using double buffering and support for stereoscopic 3D means 4 color buffers (back left & right, front left & right).

 

Another question would be, does the stencil buffer uses it's own memory, or is it shared with another buffer (say the depth buffer)?

 

Also, i've read somewhere that multisample requires a buffer per sample (say a 4x Multisample would require 4 buffers). If anyone could enlighten me at this, i'd appreciate it very much.

 

I'm nol yet accounting for user created buffers (like geometry buffers user for deferred shading, or a custom, floating point, depth buffer for HDR).

 

As a last note, is it correct to assume that all this things that can be created by the graphics API (OpenGL in this case) reside on the VRAM, or are there exceptions?

 

If something is not clear, then i'll be happy to explain.

 

Thanks in advance.

Edited by __SKYe

Share this post


Link to post
Share on other sites

Oh no, i'm talking about calculating the amount of VRAM used, from within the game/application.

Something like what you do with your custom memory manager to keep track of how much RAM you've allocated, and where allocations are going.

 

GPU-Z is an offline utility to get GPU information right?

Edited by __SKYe

Share this post


Link to post
Share on other sites

Thanks, that's helpful to know if you're within VRAM budget.

 

But while it is helpful to know the amount of memory used, it still won't help much with what i'm after.

 

You see, what i mean to do is basically to keep track of how much memory i allocate for the various types of data that resides in the VRAM.

This can be textures, vertex/normal/texcoords data, the color/depth/stencil buffers, etc.

 

Again, i don't mean to track every single byte of memory that is in the GPU, i just want to keep an "in-house" estimate of the VRAM used.

 

As an example, think of how you would create your own memory (normal RAM) tracker, to get stats like:

 

General:   2312083KB

Audio:         195421KB

MAP:       29383467KB

 

etc...

 

And the VRAM equivalent could be:

 

Color Buffers:     503918214KB

Depth Buffer:        78216928KB

Textures:        23487654303KB

Geometry:          489279345KB

 

etc...

 

Note that i don't mean to query the GPU for the amount of data i sent, or the memory in use.

What i'd do is to calculate the amount of memory a resource would use when i create/upload it in/to the GPU.

 

Again, image i load a R8G8B8A8 128x128 (uncompressed) texture from disk, and upload it to the GPU. Here i'd calculate the memory required for the texture (which would be 128*128*4 -- assuming the internal storage is also RGBA, etc) and perhaps add it to a counter of the total texture memory used.

 

I know that the GPU can remove textures from the VRAM if you upload more textures than the available memory, among other issue, so it's just an estimate.

 

Sorry if the explanation isn't clear.

 

Thanks again.

Share this post


Link to post
Share on other sites

The logic behind all your reasoning is correct.

 

However the driver and hw internals can screw your calculations completely.

 

Even though you request one Front buffer and 2 backbuffers, the GPU may actually internally have like 3 copies of them for pipelining and avoiding stalls, etc; and you have no idea to know what the driver is doing behind your back (that's the main point about the yet-unreleased Mantle, the API doesn't do stuff behind your back).

The duplication thing may even further if the GPU is in Crossfire/SLI mode.

 

For example, in many GeForce architectures (actually, AFAIK all of them) if you request an FBO of Float R16; internally the driver will use a Float F32 since their GPUs don't natively support R16 (but this may change in the future, and you don't always know this kind of stuff; this is only known because F32/F16 are both a very used and abused format, and NVIDIA has stated this explicitly many times in their GDC courses).

 

As for 32-bit colour framebuffers with 16-bit depth buffers, forget about it. It's been a very long time since I've seen a GPU that can mix colour and depth buffers of different bitdepths (use all 16-bit or all 32-bit). It either fails or internally just uses the largest bpp.

 

Same issues with the stencil buffer: In some architectures it will be shared with the depth buffer, i.e. 24 bits for the depth, 8 bits for stencil.

In other archs, they're separate (32 for depth or 24 for depth + 8 unused, and then another buffer with 8 for stencil)

 

As for MSAA, this will enlighten you (basically, 4x antialiasing = 4x the resolution of a colour and depth buffer; plus a buffer at 1x resolution to resolve. How many resolve buffer depends on how you tell the card to do it).

 

So bottom line, you can calculate your "theoretical" requirement, but the actual, real number in a particular system is completely dependent on the driver and the GPU architecture.

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  

  • Forum Statistics

    • Total Topics
      628285
    • Total Posts
      2981837
  • Similar Content

    • By mellinoe
      Hi all,
      First time poster here, although I've been reading posts here for quite a while. This place has been invaluable for learning graphics programming -- thanks for a great resource!
      Right now, I'm working on a graphics abstraction layer for .NET which supports D3D11, Vulkan, and OpenGL at the moment. I have implemented most of my planned features already, and things are working well. Some remaining features that I am planning are Compute Shaders, and some flavor of read-write shader resources. At the moment, my shaders can just get simple read-only access to a uniform (or constant) buffer, a texture, or a sampler. Unfortunately, I'm having a tough time grasping the distinctions between all of the different kinds of read-write resources that are available. In D3D alone, there seem to be 5 or 6 different kinds of resources with similar but different characteristics. On top of that, I get the impression that some of them are more or less "obsoleted" by the newer kinds, and don't have much of a place in modern code. There seem to be a few pivots:
      The data source/destination (buffer or texture) Read-write or read-only Structured or unstructured (?) Ordered vs unordered (?) These are just my observations based on a lot of MSDN and OpenGL doc reading. For my library, I'm not interested in exposing every possibility to the user -- just trying to find a good "middle-ground" that can be represented cleanly across API's which is good enough for common scenarios.
      Can anyone give a sort of "overview" of the different options, and perhaps compare/contrast the concepts between Direct3D, OpenGL, and Vulkan? I'd also be very interested in hearing how other folks have abstracted these concepts in their libraries.
    • By aejt
      I recently started getting into graphics programming (2nd try, first try was many years ago) and I'm working on a 3d rendering engine which I hope to be able to make a 3D game with sooner or later. I have plenty of C++ experience, but not a lot when it comes to graphics, and while it's definitely going much better this time, I'm having trouble figuring out how assets are usually handled by engines.
      I'm not having trouble with handling the GPU resources, but more so with how the resources should be defined and used in the system (materials, models, etc).
      This is my plan now, I've implemented most of it except for the XML parts and factories and those are the ones I'm not sure of at all:
      I have these classes:
      For GPU resources:
      Geometry: holds and manages everything needed to render a geometry: VAO, VBO, EBO. Texture: holds and manages a texture which is loaded into the GPU. Shader: holds and manages a shader which is loaded into the GPU. For assets relying on GPU resources:
      Material: holds a shader resource, multiple texture resources, as well as uniform settings. Mesh: holds a geometry and a material. Model: holds multiple meshes, possibly in a tree structure to more easily support skinning later on? For handling GPU resources:
      ResourceCache<T>: T can be any resource loaded into the GPU. It owns these resources and only hands out handles to them on request (currently string identifiers are used when requesting handles, but all resources are stored in a vector and each handle only contains resource's index in that vector) Resource<T>: The handles given out from ResourceCache. The handles are reference counted and to get the underlying resource you simply deference like with pointers (*handle).  
      And my plan is to define everything into these XML documents to abstract away files:
      Resources.xml for ref-counted GPU resources (geometry, shaders, textures) Resources are assigned names/ids and resource files, and possibly some attributes (what vertex attributes does this geometry have? what vertex attributes does this shader expect? what uniforms does this shader use? and so on) Are reference counted using ResourceCache<T> Assets.xml for assets using the GPU resources (materials, meshes, models) Assets are not reference counted, but they hold handles to ref-counted resources. References the resources defined in Resources.xml by names/ids. The XMLs are loaded into some structure in memory which is then used for loading the resources/assets using factory classes:
      Factory classes for resources:
      For example, a texture factory could contain the texture definitions from the XML containing data about textures in the game, as well as a cache containing all loaded textures. This means it has mappings from each name/id to a file and when asked to load a texture with a name/id, it can look up its path and use a "BinaryLoader" to either load the file and create the resource directly, or asynchronously load the file's data into a queue which then can be read from later to create the resources synchronously in the GL context. These factories only return handles.
      Factory classes for assets:
      Much like for resources, these classes contain the definitions for the assets they can load. For example, with the definition the MaterialFactory will know which shader, textures and possibly uniform a certain material has, and with the help of TextureFactory and ShaderFactory, it can retrieve handles to the resources it needs (Shader + Textures), setup itself from XML data (uniform values), and return a created instance of requested material. These factories return actual instances, not handles (but the instances contain handles).
       
       
      Is this a good or commonly used approach? Is this going to bite me in the ass later on? Are there other more preferable approaches? Is this outside of the scope of a 3d renderer and should be on the engine side? I'd love to receive and kind of advice or suggestions!
      Thanks!
    • By nedondev
      I 'm learning how to create game by using opengl with c/c++ coding, so here is my fist game. In video description also have game contain in Dropbox. May be I will make it better in future.
      Thanks.
    • By Abecederia
      So I've recently started learning some GLSL and now I'm toying with a POM shader. I'm trying to optimize it and notice that it starts having issues at high texture sizes, especially with self-shadowing.
      Now I know POM is expensive either way, but would pulling the heightmap out of the normalmap alpha channel and in it's own 8bit texture make doing all those dozens of texture fetches more cheap? Or is everything in the cache aligned to 32bit anyway? I haven't implemented texture compression yet, I think that would help? But regardless, should there be a performance boost from decoupling the heightmap? I could also keep it in a lower resolution than the normalmap if that would improve performance.
      Any help is much appreciated, please keep in mind I'm somewhat of a newbie. Thanks!
    • By test opty
      Hi,
      I'm trying to learn OpenGL through a website and have proceeded until this page of it. The output is a simple triangle. The problem is the complexity.
      I have read that page several times and tried to analyse the code but I haven't understood the code properly and completely yet. This is the code:
       
      #include <glad/glad.h> #include <GLFW/glfw3.h> #include <C:\Users\Abbasi\Desktop\std_lib_facilities_4.h> using namespace std; //****************************************************************************** void framebuffer_size_callback(GLFWwindow* window, int width, int height); void processInput(GLFWwindow *window); // settings const unsigned int SCR_WIDTH = 800; const unsigned int SCR_HEIGHT = 600; const char *vertexShaderSource = "#version 330 core\n" "layout (location = 0) in vec3 aPos;\n" "void main()\n" "{\n" " gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n" "}\0"; const char *fragmentShaderSource = "#version 330 core\n" "out vec4 FragColor;\n" "void main()\n" "{\n" " FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n" "}\n\0"; //******************************* int main() { // glfw: initialize and configure // ------------------------------ glfwInit(); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // glfw window creation GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "My First Triangle", nullptr, nullptr); if (window == nullptr) { cout << "Failed to create GLFW window" << endl; glfwTerminate(); return -1; } glfwMakeContextCurrent(window); glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); // glad: load all OpenGL function pointers if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) { cout << "Failed to initialize GLAD" << endl; return -1; } // build and compile our shader program // vertex shader int vertexShader = glCreateShader(GL_VERTEX_SHADER); glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr); glCompileShader(vertexShader); // check for shader compile errors int success; char infoLog[512]; glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success); if (!success) { glGetShaderInfoLog(vertexShader, 512, nullptr, infoLog); cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << endl; } // fragment shader int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr); glCompileShader(fragmentShader); // check for shader compile errors glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success); if (!success) { glGetShaderInfoLog(fragmentShader, 512, nullptr, infoLog); cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << endl; } // link shaders int shaderProgram = glCreateProgram(); glAttachShader(shaderProgram, vertexShader); glAttachShader(shaderProgram, fragmentShader); glLinkProgram(shaderProgram); // check for linking errors glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success); if (!success) { glGetProgramInfoLog(shaderProgram, 512, nullptr, infoLog); cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << endl; } glDeleteShader(vertexShader); glDeleteShader(fragmentShader); // set up vertex data (and buffer(s)) and configure vertex attributes float vertices[] = { -0.5f, -0.5f, 0.0f, // left 0.5f, -0.5f, 0.0f, // right 0.0f, 0.5f, 0.0f // top }; unsigned int VBO, VAO; glGenVertexArrays(1, &VAO); glGenBuffers(1, &VBO); // bind the Vertex Array Object first, then bind and set vertex buffer(s), //and then configure vertex attributes(s). glBindVertexArray(VAO); glBindBuffer(GL_ARRAY_BUFFER, VBO); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0); glEnableVertexAttribArray(0); // note that this is allowed, the call to glVertexAttribPointer registered VBO // as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind glBindBuffer(GL_ARRAY_BUFFER, 0); // You can unbind the VAO afterwards so other VAO calls won't accidentally // modify this VAO, but this rarely happens. Modifying other // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind // VAOs (nor VBOs) when it's not directly necessary. glBindVertexArray(0); // uncomment this call to draw in wireframe polygons. //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); // render loop while (!glfwWindowShouldClose(window)) { // input // ----- processInput(window); // render // ------ glClearColor(0.2f, 0.3f, 0.3f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // draw our first triangle glUseProgram(shaderProgram); glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to // bind it every time, but we'll do so to keep things a bit more organized glDrawArrays(GL_TRIANGLES, 0, 3); // glBindVertexArray(0); // no need to unbind it every time // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.) glfwSwapBuffers(window); glfwPollEvents(); } // optional: de-allocate all resources once they've outlived their purpose: glDeleteVertexArrays(1, &VAO); glDeleteBuffers(1, &VBO); // glfw: terminate, clearing all previously allocated GLFW resources. glfwTerminate(); return 0; } //************************************************** // process all input: query GLFW whether relevant keys are pressed/released // this frame and react accordingly void processInput(GLFWwindow *window) { if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) glfwSetWindowShouldClose(window, true); } //******************************************************************** // glfw: whenever the window size changed (by OS or user resize) this callback function executes void framebuffer_size_callback(GLFWwindow* window, int width, int height) { // make sure the viewport matches the new window dimensions; note that width and // height will be significantly larger than specified on retina displays. glViewport(0, 0, width, height); } As you see, about 200 lines of complicated code only for a simple triangle. 
      I don't know what parts are necessary for that output. And also, what the correct order of instructions for such an output or programs is, generally. That start point is too complex for a beginner of OpenGL like me and I don't know how to make the issue solved. What are your ideas please? What is the way to figure both the code and the whole program out correctly please?
      I wish I'd read a reference that would teach me OpenGL through a step-by-step method. 
  • Popular Now