Sign in to follow this  
space_cadet

OpenGL OpenGL ES 2.0 on Android: how to render 500 cubes effectively

Recommended Posts

Hi,

I am trying to simulate a starfield of rotating cubes moving towards the user:

[img]http://i.imgur.com/7d9zu.png[/img]

I am struggling to maintain a smooth animation on Android. I can't see why a Dual-core 1 GHz Cortex-A9 with a ULP GeForce GPU should not be able to do that. Here's what I do:

INITIALIZATION:

- Create a VBO containing 36 cube position vertices and 36 cube normal vertices, interleaved
- Set up a simple shader that takes positions, normals, color, MV matrix, MVP matrix, light position
- Connect the VBO to the shader's position and normal attribute respectively

EACH FRAME:

a] Movement (for each cube)

- calculate scaling matrix, rotation matrix A, translation matrix, rotation matrix B
- multiply all of the above matrices to obtain model matrix
- multiply model matrix and view matrix to obtain MV matrix
- multiply MV matrix and projection matrix to obtain MVP matrix

b] Draw (for each cube)

- hook up cube's MV matrix with shader (glUniformMatrix4fv)
- hook up cube's MVP matrix with shader (glUniformMatrix4fv)
- hook up cube's color constant with shader (glVertexAttrib4f)
- draw cube (glDrawArrays)

I have done a lot of profiling and timing analyzation, so I don't think I have any unintended performance leaks in my code. Rather, I believe there is a more general design flaw, and I hope someone can help me improve it.

Share this post


Link to post
Share on other sites
Do you have any profiling tools that allow you to measure CPU and GPU timings independently? The first step will be determining which processor is the bottleneck, so you can focus your optimisations usefully.

That said, a solution will probably involve call glDraw less often than once-per-cube.
On the CPU side, every "batch" of geometry has a certain amount of overhead, so you want to reduce the total amount of [font=courier new,courier,monospace]gl*[/font] calls, particularly [font=courier new,courier,monospace]glDraw*[/font] calls.
On the GPU side, you want every [font=courier new,courier,monospace]glDraw*[/font] "batch" to contain as many vertices and as many pixels as possible. It seems like many of your cubes cover hardly any pixels, which may greatly exaggerate the per-draw overheads.

Share this post


Link to post
Share on other sites
[quote name='Hodgman' timestamp='1353758793' post='5003722']That said, a solution will probably involve call glDraw less often than once-per-cube.[/quote]

True, but [i]how[/i] ? Since every cube needs its own scaling, rotation and translation, how can I combine glDrawArrays() calls?

Share this post


Link to post
Share on other sites
[quote name='space_cadet' timestamp='1353759859' post='5003725']
[quote name='Hodgman' timestamp='1353758793' post='5003722']That said, a solution will probably involve call glDraw less often than once-per-cube.[/quote]

True, but [i]how[/i] ? Since every cube needs its own scaling, rotation and translation, how can I combine glDrawArrays() calls?
[/quote]

Option 1: Software transform the vertices. That is, do the matrix multiply on the CPU, then you can send all the cubes in one go.
Option 2: 'Hardware skinning' style solution. Instead of doing one cube at a time, put 16* cubes into your VBO. The vertices for each cube have indices, which you use in your vertex shader to look up into an array of matrix uniforms.

From experience doing similar things on iOS, I'd expect option 1 to be the better choice.

*Probably you'll want this number to be as large as possible within the constaints of the max amount of uniform space your GPU supports. Edited by C0lumbo

Share this post


Link to post
Share on other sites

I know this thread is a month old, but I have invested serious thought and work into the project, and I'd like to post an update to show that I aprecciate your answers, and to help other people with similar issues.

 

 

PROFILING

 

 

Do you have any profiling tools that allow you to measure CPU and GPU timings independently? The first step will be determining which processor is the bottleneck, so you can focus your optimisations usefully.

 

 

 

I believe that you have a very good point here; I have mostly been "optimizing blindly", which is considered bad practice. I have tried / considered the following options:

 

 

1. Android SDK Tools: the profiler shipped with the SDK shows CPU time, but not GPU time. Also, it profiles my own application, but I would like to see what's going on in the whole system. Google has recognized this and published a tool for system-wide profiling called systrace, but it's only available for Jelly Bean. The same goes for dumpsys gfxinfo which in combination with the Jelly Bean developer option "Profile GPU Rendering" outputs a stat about how much time is spent processing, drawing and swapping UI. See Chet Haase and Guy Romain's excellent presentation about Android UI performance for more information about those tools. For me, they are not an option, I am stuck with Honeycomb for various reasons.

 

 

 

2. Log output: yes I know it is stone age, but I thought it would be interesting to see how much time my application spends in my move() (CPU) and draw() (GPU) methods. The results are not very conclusive; I guess this has to to with multithreading and the way Android handles vsync.

 

 

3. NVIDIA Tools: there is a tool for Tegra 2 platforms called PerfHUD ES that looks very promising: detailed information about draw calls and lots of other GPU-related information. I am currently trying to get this running on honeycomb. Any help aprecciated.

 

 

OPTIMIZING

 

 

 

Option 1: Software transform the vertices. That is, do the matrix multiply on the CPU, then you can send all the cubes in one go.
Option 2: 'Hardware skinning' style solution. Instead of doing one cube at a time, put 16* cubes into your VBO. The vertices for each cube have indices, which you use in your vertex shader to look up into an array of matrix uniforms.

 

 

 

Both of your options seem very reasonable approaches to take. I decided to implement option 2 first. The OpenGL ES specification calls this method "Dynamic Indexing".  It took me an hour to rearrange my application accordingly, and a whole day to find out how to get hold of the vertex index inside the shader and use it to address my transformation matrices. It's not straightforward on OpenGL ES 2.0 because for some fucking reason they decided to leave out the crucial gl_VertexID variable there. Sorry, but this tiny little detail really drove me mad. Anyways, the solution is quite simple, once you know how to do it. Anton Holmquist has a short, to-the-point blog post about it, which I wish I'd found earlier.

 

The one big drawback about this method is, like you pointed out, the limited uniform space. For those who don't have a clue what that is (like I did): it is the space available for declaring uniform variables in the shader. I read somewhere that this space relates to the amount / size of registers the GPU has - correct me if I'm wrong here. For anyone interested, calling glGetIntegerv(GL_MAX_VERTEX_UNIFORM_VECTORS) will return a number that says how much uniform space you have on your system. The specification for OpenGL ES 2.0 says it has to be at least 128. The number is expressed in vectors, and since each matrix has 4 vectors, that means you could declare a maximum of 32 matrix variables or, in my case, two arrays of 16 matrices. In other words, I can batch a maximum of 16 cubes now. 

 

 

NEXT

 

Dynamic indexing has certainly improved performance, but I am not entirely happy yet. I will implement the abovementioned option 1, hoping to improve performance by shifting work from the GPU to the CPU and, as a next step, parallize the move() and draw() operations.

Share this post


Link to post
Share on other sites

Doing the the matrix calculations in software shouldn't be too bad. But if you are CPU limited (maybe the case on Android) then here is an alternative that does the matrix calculation on the GPU:

 

Pass a vec4 Rotation (rotX, rotY, rotZ, angle) to your vertex shader. Then calculate the rotation matrix in your shader:

 

[code]mat4 transform = mat4(1.0); //identity   ... make rotation matrix from axis and angle ...   gl_Position = projection * view * transform * a_position;[/code]

 

Theoretically you could put the Position and Normal attributes into a separate static VBO since they are unchanged (and update the view matrix instead). If you fill all your instance data in one go, you could end up with a single draw call per frame.

Share this post


Link to post
Share on other sites
I do think the software approach will beat the vertex shader approach, so you should probably go ahead and give that a shot.

But - I think you should be able to manage more than 16 cubes per batch. Firstly, you don't need a full 4x4 matrix - you can switch to 4x3 matrices and implicitly assume that the last row is 0, 0, 0, 1. You might need to transpose your matrices to achieve this.

Also, I don't think you need two arrays of matrices. I assume one of the matrices is for your normals, and one for the positions. But you can usually use the same matrix for your positions and your normals and simply ignore the position for the normals.

So, by my reckoning you should be able to manage 128/3=42 cubes each batch. Your GLSL code might end up looking a bit like this (untested, not compiled):

uniform float4 g_vMatrices[42*3];

...

vWorldPos.x = dot(g_vMatrices[iCubeIndexAttribute*3], float4(vPositionAttribute, 1.0));
vWorldPos.y = dot(g_vMatrices[iCubeIndexAttribute*3+1], float4(vPositionAttribute, 1.0));
vWorldPos.z = dot(g_vMatrices[iCubeIndexAttribute*3+2], float4(vPositionAttribute, 1.0));
vWorldNormal.x = dot(g_vMatrices[iCubeIndexAttribute*3], float4(vNormalAttribute, 0.0));
vWorldNormal.y = dot(g_vMatrices[iCubeIndexAttribute*3+1], float4(vNormalAttribute, 0.0));
vWorldNormal.z = dot(g_vMatrices[iCubeIndexAttribute*3+2], float4(vNormalAttribute, 0.0));


Oops - just realised you'd then need to transform the positions by the viewproj matrix which will take up a few more uniforms, so you'll end up with only 41 cubes per batch. Edited by C0lumbo

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
      628275
    • Total Posts
      2981763
  • 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