Sign in to follow this  
Prune

OpenGL HDR multisampling AA looks poor for high contrast edges

Recommended Posts

I'm using 16x8 coverage multisampling (tried regular as well, with same results) in an OpenGL program, with 16 bit floating point textures and FBOs. The AA looks fine for edges that do not form very high contrast against their background. But if, for example, the edge is reflecting an bright area from the HDR environment map, and is against a background that is not very bright itself, the AA looks quite poor, almost as if there wasn't any. I'm guessing this has to do with the fact that tone mapping is done after the multisampling, but obviously that cannot be the other way around, unless I'm missing something... So, what's the best way to improve quality? Here's a screenshot, showing AA working OK except where the edge goes across the brightest part of the reflection:

Share this post


Link to post
Share on other sites
Yes, it's because you're doing tonemapping after MSAA.

I'm not sure about OpenGL, but in Direct3D10 custom multisample resolve allows you to do just that - multisample after you do your tonemapping. The feature should be available on all Direct3D10 compliant hardware - it's just a matter of whether or not OpenGL exposes this functionality.

Share this post


Link to post
Share on other sites
Is there a standard name for this? "custom mutlisample" or "custom multisampling" do not return many results in Google.

I should also note that with HDR textures the analogous problem exists, because the texture resampling is done before tone-mapping, and high contrast image edges make it look as if nearest neighbor was used instead of bilinear/mipmapped interpolation. Is there custom interpolation in Direct3D for textures as well?

I'm guessing that when I add bloom it would hide the poor AA a bit, since the bloom has most effect in exactly such high contrast areas, but that's kind of like trying to sweep the problem under the rug and is not a robust solution.

As a side question, should bloom be computed before or after tone-mappin? My guess is that the correct way would be that it should be before, since if it's done after, then two areas of the same size that are both saturated after tone-mapping, but have different true brightness, would end up having identical bloom amount, which is obviously wrong.

Share this post


Link to post
Share on other sites
Quote:
Original post by Prune
As a side question, should bloom be computed before or after tone-mappin? My guess is that the correct way would be that it should be before, since if it's done after, then two areas of the same size that are both saturated after tone-mapping, but have different true brightness, would end up having identical bloom amount, which is obviously wrong.

The point of tone-mapping is to adapt an HDR image down to LDR. I believe that bloom should be done before tonemapping, while still in HDR space. However, bloom shouldn't contribute to a scene's luminance.

Share this post


Link to post
Share on other sites
Iv had this same exact problem. What i ended up doing was doing the tonemapping not as a post process, but at the end of my main material shaders. This way, the color gets tonemapped down to an acceptable range before actually rendering the sample, allowing the edges to be properly antialiased.

Another advantage to this is that you dont even need a floating point surface since the color is tonemapped anyway (assuming you saturate the tonemapped color). Unless of coarse you also want bloom, then you dont saturate and write out to a floating point surface

Share this post


Link to post
Share on other sites
A common problem. Even some offline renderers have this problem. Actually, multisampling after tonemapping is mathematically incorrect too (since the post-tonemap samples aren't linear anymore). But compared to the jaggies, it's usually more pleasing visually.

I have recently done some experimentation with a special adaptive tonemapper, that takes edge contrast into account. The idea is to detect steep interpolation gradients (as they are created by multisampling a HDR surface with high contrast) and decrease exposure along these edges. It works quite well, but I still get some annoying sparkling artifacts, probably due to lacking precision at the differencing pass.

Doing this isn't even that far fetched, since the human visual system does something similar in the real world.

Share this post


Link to post
Share on other sites
I guess technically it wouldnt be correct, i hadnt actually thought about that until now; Though, I believe that the source engine does their tonemapping the way i described also; so either they have a special way to do transparency or its not noticable enough to tell :p

Actually, i can think of one way around it. WHen you render transparents, dont enable blending, but rather read the backbuffer and "un-tonemap" the color you read, then do your blending in the shader, tonemap the new color, and return that.
A drawback here is that if you want to draw one transparent on another, you have to do some render target changing...

Share this post


Link to post
Share on other sites
Quote:
Original post by coderchris
Iv had this same exact problem. What i ended up doing was doing the tonemapping not as a post process, but at the end of my main material shaders.

With this, you can then only use local tone-mapping operators.

Share this post


Link to post
Share on other sites
Quote:
Original post by Prune
Quote:
Original post by coderchris
Iv had this same exact problem. What i ended up doing was doing the tonemapping not as a post process, but at the end of my main material shaders.

With this, you can then only use local tone-mapping operators.


That's not true, Half Life 2 was doing just that : rendering everything to a LDR target, doing the tonemapping at the end of every shader. Their tone mapping operator was a global one (a simple division by a constant exposure value).

Quote:
If I implement tonemapping in the shaders, wouldn't the alpha-blending be incorrect then since it would be done in a nonlinear color space?


Yes it's partially incorrect to do alpha blending in the tone mapped space : a semi transparent object drawn on top of an overbright object will not maintin the correct brightness, instead the shining object will look dull. But it's a compatibility trade off (something that allowed Half Life 2 to run on any shadermodel 2.0 card). This is true for any post processing effect (motion blur, depth of field, realistic bloom, haloing, fog etc.)

If you rely on high quality multisampling/alphablending you should do the Direct3D10 version, that is you should read the samples individually in a pixel shader after you've finished with the whole scene, tone map them and do the downsampling.

You should note that the problem you're seeing with edge antialiasing is also true for any filtering that happened before your tone mapping operator and that includes anisotropic filtering. An element that people often forget or dismiss totally. Anistropic filtering is designed to work optimally in linear space.

That problem with anisotropic cannot be fixed simply by doing the filter after the tone mapping (because it happens at texture read in a fixed function texture unit). Some level of supersampling might help.

---

There a third way, but I haven't seen implemented anywhere. I planned of doing a tutorial on it someday.. The idea is that you could maintain the true brightness ratio locally but not globally, that way things like anti aliasing that rely on the linearity but only on neighboring pixels could be applied at any stage of the rendering pipeline.

LeGreg

Share this post


Link to post
Share on other sites
Quote:
Original post by LeGreg
There a third way, but I haven't seen implemented anywhere. I planned of doing a tutorial on it someday.. The idea is that you could maintain the true brightness ratio locally but not globally, that way things like anti aliasing that rely on the linearity but only on neighboring pixels could be applied at any stage of the rendering pipeline.

Sounds interesting. Any more details ?

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
      628284
    • Total Posts
      2981831
  • 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