Sign in to follow this  
LittleJimmy

OpenGL Ideas for rendering stacked UI elements

Recommended Posts

Hello Everyone,

I've developed a basic theme able user interface system with opengl by drawing different shapes and text. I want the UI to be used on both mobile and desktop so I only want the UI to redraw when absolutely necessary in order to conserve battery life. So there is no rendering call in the main application loop. The time to paint can be at anytime a UI control believes it requires a redraw.

The issue that I'm having is that I can't figure out how to only draw the Control that needs redrawing. If the control that needs redrawing is semi transparent, the control behind it will need to be redrawn as well due to the fact that the redraw causes an opengl clear in the control's scissor rect, but if the control behind the control that needs redrawing is redrawn, all controls behind that and inside of that will need to be redrawn as well. To the point where I'm redrawing the entire screen every time something changes in one control. This has come to a head where I'm attempting to draw a textbox control and every time the caret blinks I'm redrawing all the controls on the screen, which doesn't seem very efficient.

Does anybody have any ideas or suggestions for ways in which I could draw semi transparent controls sitting on top of each other without redrawing the entire screen?

Thanks,

Share this post


Link to post
Share on other sites

1. How sure are you that you're ACTUALLY being a power drain? Reason -- this is how all the rendering code on phones works and so the OS and GPU designers are really, really good at making them use very little power. Implement your basic version and use GPU debugging tools to see what workload you're actually generating..

2. Clip to the smallest changed area. Draw everything as you otherwise would. The clipping will cull out the areas that don't need rendering. Most mobile devices use tile-based renderings; the screen is rendered in squares, each of which accumulates its own processing list of primitive operations and they're rasterised/fragment processed independently. Draws which don't touch a lot of the tiles because they're clipped out incur no cost; the clipping ensures you're touching as few as possible. This is really all you should need to do. This only works for polygon clipping though, not stencil buffers. (You're after being able to discard geometry portions, not fragments).

3. There's a BUNCH of other "tricks" which *could* be used depending on exactly the drawing architecture you've got -- however, the last time I actually used any of them was on 8-bit micros where brute-force solutions like "redraw the whole screen" just weren't happening[1]. TBH, given that mid-range phones have **six to seven orders of magnitude** more processing power... you shouldn't need to be going there.

Seriously -- trust the machine developers, measure your impact and only optimise later.

Heck; if it comes to that --

4. Does your caret really need to blink? The cheapest geometry is geometry you don't draw at all...

 

[1] As an example, you grab a copy of the area under your caret. Now you can erase it to make it blink without needing a full redraw... Once you have a copy of the area without it and the screen buffer containing a version with the caret, you can just swap the memory areas over and save doing any drawing at all... See how strained that's all going to get?

Share this post


Link to post
Share on other sites

No I'm not positive that I am actually being a power drain. what I'm doing is I'm checking the CPU usage through the task manager while I let the application run. In my mind, if all the app is doing is blinking a cursor, CPU usage should be 0%. (I checked visual studio, and with all its UI complexity, when it just sits and blinks a cursor, its CPU usage is 0%).

Granted, checking the task manager probably isn't the most scientific and rigorous way to test performance.

Your answer did get me thinking though, and I made the Text box request a repaint every time the cursor blinked. Even though the UI was being re rendered every time the cursor blinked, its was still only using 0% CPU as well. So yeah, maybe I am too concerned about performance and power usage.

The problem with clipping to the smallest change areas is if the controls are semi transparent. If a small textbox control sitting in the center of a Form is semi transparent, I need to render it and the background Form control as well in order to get the final blend colour between the 2 controls. If that Form is filling the entire screen, I have to re render the entire screen (along with all the other controls in the Form as well).

The only thing I can think of is to perhaps run though all the controls and their children, test if they intersect the rect being redrawn, and only redraw the controls (and their parent controls as well) if they intersect, but I wasn't sure if that was the most efficient way to do things or if I was actually wasting my time and should just rather do a brute force redraw every time instead.

Thanks

Share this post


Link to post
Share on other sites

The problem with clipping to the smallest change areas is if the controls are semi transparent. If a small textbox control sitting in the center of a Form is semi transparent, I need to render it and the background Form control as well in order to get the final blend colour between the 2 controls. If that Form is filling the entire screen, I have to re render the entire screen (along with all the other controls in the Form as well).

Why do you think that? If you just draw that background inside the changed rectangle you do not overdraw anything outside it and therefore you do not need to redraw anything else outside it. (You either just change the draws to be only inside or use scissor.)

Share this post


Link to post
Share on other sites

"only redraw the controls (and their parent controls as well) if they intersect"

The GL renderer is *already* doing that work (because it can't know you pre-clipped everything). Possibly it can even do it in hardware..

Just throw your geometry at it, let it sort it all out. Don't worry about it unless it's actually a problem.

Share this post


Link to post
Share on other sites

Okay cool, so what I've begun to realize now is that I don't actually have to worry about sending opengl geometry outside the clip region, since it will deal with that itself (right?). What that has now done is shifted the problem from an being opengl one to something less specific and more general to graphics programming, something akin maybe to software culling perhaps?

The problem now is ensuring that controls that don't actually need to be rendered, don't send vertices through the pipeline in the first place, since opengl is going to discard them any way, and its costing CPU resources to build all those vertices. To that end, I'm no longer sure if this still the right place for the question. 

But, given a control hierarchy, where each Paint() call runs through the hierarchy generating vertices for all controls and their children, is there a high performance solution that allows me to discard controls if they don't intersect the rect that needs redrawing? Right now, my only idea is to pass around the rect that will be redrawn and any control that doesn't intersect that rect doesn't get its vertices generated and sent to the GPU. My only concern is in situations where a tiny little square in the corner is being animated, but I now have to run through 300 other controls checking all of their rects every frame, seems a bit intensive, but at the same time, I'm guessing still cheaper than generating the vertices for those controls.

I hope I'm getting my concerns across properly?

Thanks,

Edited by LittleJimmy

Share this post


Link to post
Share on other sites

The controls form a tree. A dialogue contains a couple of panes, the panes contain controls, the controls contain some static text and an entry box and so on on.

If the outer control completely contains the inner controls, it can check if the redraw is within its bounds and if not... doesn't propagate it to the contained controls.

 

This is how most real-world UI rendering systems operate -- boxes within boxes within boxes. It's common to Windows, MacOS, X11. It's happening inside web browsers and it's also the case for most mobile phone UIs. It's not the only solution, but it's a well worked one.

Most UIs with non-transparent elements can optimise further (because it's only the top-most opaque object which needs to paint). You'll have to exhaustively run through ALL the nodes and paint them in reverse stacking order.

 

The other solution is to use several drawing layers. You draw each UI elements to one as if opaque and composite the outputs together afterwards. This needs more memory and more GPU power but less CPU work.

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  

  • Announcements

  • Forum Statistics

    • Total Topics
      628300
    • Total Posts
      2981900
  • 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