Sign in to follow this  
EvilNando

OpenGL Big problem sorting sprites

Recommended Posts

So Ive made a little 2D engine using OpenGL.

It uses VBO and VBA for storing batches of quads before sending those to the GPU


my current problem is that my game requires at minimum 3 different textures to be able to render a whole scene ( this cannot be changes so please dont suggest to only use one texture instead )

Ive manages to overcome this problem by using 3dtextures the problem is that the extension that allows me to do this is only available on DX11 hardware which is unacceptable for our intended target platforms

So what Im looking for is a way to be able to switch textures withing a single glDrawElements call ( Which Im thinking is impossible )

Thanks

Share this post


Link to post
Share on other sites
[quote name='FlyingDutchman' timestamp='1318078882' post='4870480']
So u want to bind 3 textures and than use one call to draw? IMO its not possible.

why don't u pack all 3 textures in one big texture? Than u create 3 Texture Buffers with the different coordinates and switch this one than ...
[/quote]

Because the amount of needed textures can vary (the minimum being 3)

Share this post


Link to post
Share on other sites
Simple answer; you can't.

Thing which are bound to the pipeline can not change during the execution of a draw command.

Less simple answer;
As you've already hinted at texture arrays (not 3D textures, those are different and have worked since the GF3 days) allow you to select a texture by 'layer' but as you say this is only on recent hardware.

You can simulate it however by having multiple samplers and then with each instance you have an id which indicates, via a simple 'if' statement which sampler to read for the texture data. As all the pixels in an execution will head the same way then the overhead will be minimal (cost of the if statement). You might even be able to use an array of samplers, each with a texture bound, and use the id value to reference the correct sampler directly, however I'm not sure when glsl/hardware support for that came in.

Share this post


Link to post
Share on other sites
Probably the best solution to sort the vertex list by texture and render it in three goes, but doing that on the host might be more expensive in terms of host CPU and transfer.

It might actually be faster to render the VBO several times, binding a different texture each time. Set a uniform to tell the vertex shader which texture is bound. If it's the "wrong" one, it can just output (0,0,0). That'll be degenerate quads/tris and there should be no frag runs at all.

You should be able to do this in the vshader without an if statement by suitable application of the built-in functions. (Using divisions/floor/ceil etc to arrive a number which is either 0.0 or 1.0 depending on if this pass is invalid or valid and then multiplying the final output by that)

The reason for doing this is that branches are *extremely* expensive operations in the large parallel nVidia/ATI architectures; it's actually faster in many cases to do more work and multiply by zero at the end than to branch around the instructions.

Things like array-of-sampler are annoyingly driver/card dependent. Try them and if the compiler says yes, then hurrah, but you need a fallback plan.

Share this post


Link to post
Share on other sites
[quote name='Katie' timestamp='1318085291' post='4870500']
Probably the best solution to sort the vertex list by texture and render it in three goes, but doing that on the host might be more expensive in terms of host CPU and transfer.

It might actually be faster to render the VBO several times, binding a different texture each time. Set a uniform to tell the vertex shader which texture is bound. If it's the "wrong" one, it can just output (0,0,0). That'll be degenerate quads/tris and there should be no frag runs at all.

You should be able to do this in the vshader without an if statement by suitable application of the built-in functions. (Using divisions/floor/ceil etc to arrive a number which is either 0.0 or 1.0 depending on if this pass is invalid or valid and then multiplying the final output by that)

The reason for doing this is that branches are *extremely* expensive operations in the large parallel nVidia/ATI architectures; it's actually faster in many cases to do more work and multiply by zero at the end than to branch around the instructions.

Things like array-of-sampler are annoyingly driver/card dependent. Try them and if the compiler says yes, then hurrah, but you need a fallback plan.
[/quote]
I guess what Ill be doing is sort all my draw calls FIRST then start a new batch every time the next quad in the queue uses a different texture than the currently active?

Share this post


Link to post
Share on other sites
[quote name='Katie' timestamp='1318085291' post='4870500']
The reason for doing this is that branches are *extremely* expensive operations in the large parallel nVidia/ATI architectures; it's actually faster in many cases to do more work and multiply by zero at the end than to branch around the instructions.
[/quote]

I'm going to disagree here totally.

They are very costly IF different pixels/fragments in the same group take different paths, however if everyone takes the same path then the cost practically vanishes (you take some overhead from having to compute the 'if' but the branching itself is performed by the sequencer based on the information calculated), which will be the case in this instance.

Branching in shaders is FINE and has been fine on any hardware produced in the last 5 years PROVIDED you don't branch at a high frequency in the same group of pixels.

(I've done work on the 360/PS3 where branching in the pixel shader has IMPROVED the frame rate/dropped the draw time as the majority of fragments when one way or the other with a few 'border cases' needing to take both paths, although one path was a trivial 'float4 = float4(0,0,0,0)' path.)

Share this post


Link to post
Share on other sites
[quote name='EvilNando' timestamp='1318079602' post='4870483']
[quote name='FlyingDutchman' timestamp='1318078882' post='4870480']
So u want to bind 3 textures and than use one call to draw? IMO its not possible.

why don't u pack all 3 textures in one big texture? Than u create 3 Texture Buffers with the different coordinates and switch this one than ...
[/quote]

Because the amount of needed textures can vary (the minimum being 3)
[/quote]

How can the amount vary? Are the textures created during the Gameplay or what? I don't understand the problem to be honest.. Normally you know ok, i load 10 meshes a 10 textures so i will need a array of pointers to 100 textures in memory.. and than just before the glDrawXY call switch the pointer

Share this post


Link to post
Share on other sites
"They are very costly IF different pixels/fragments in the same group take different paths,"

Sorry, yes. I was unclear on this; the expense comes from having to park contexts and come back for them to run the program to completion later, so if none get parked then there isn't a problem.

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
      628277
    • Total Posts
      2981774
  • 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