Sign in to follow this  
goowik

OpenGL Rendering possibilities

Recommended Posts

Hi,

I've started learning OpenGL a few days back and love it [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img]
It's been a few months to almost a year I've been creating games in 2D, time to change!

As of now I always created my primitive objects with an immediate rendering coding
For example:
[CODE]
glBegin(GL_TRIANGLES);
glColor3f(1, 0, 0);
glVertex2f(-0.5f, -0.5f);
glColor3f(0, 1, 0);
glVertex2f(0.5f, -0.5f);
glColor3f(0, 0, 1);
glVertex2f(0.5f, 0.5f);
glEnd();
[/CODE]

After reading some articles on performances I found out there are several more rendering "patterns". There is:[list]
[*]Display lists
[*]Vertex arrays
[*]Vertex buffer object
[*]and Immediate
[/list]
Does it come to personal preferences when choosing one of them? Or is there a major difference?

Also let's say you have a cube. How can you cull 3 of the invisible sides and make it change each time you move around it.
Is this coding different per rendering pattern?

Kind regards
Peter Edited by goowik

Share this post


Link to post
Share on other sites
You are using legacy OpenGL. It is fine for testing small simple things, but not good enough for "real" applications. And it is usually not feasible to start with legacy, and then upgrade, because it is done differently.

Have a look at [url="http://www.arcsynthesis.org/gltut/"]Learning Modern 3D Graphics Programming[/url], and you will quickly learn the modern way of doing it.

Unfortunately, most of the tutorials "out there" are done in the old way.

Share this post


Link to post
Share on other sites
@lardpensjo:
Just so I understand better: By Legacy OpenGL you mean the way of writing code? Not the library I'm using?
Thanks a bunch for the link! Guess I have some work to do testing out :)

@mark ds:
okay, I guess I forgot to mention that I'm using [url="http://www.lwjgl.org/index.php"]LWJGL [/url](The Lightweight Java Game Library). But I guess the OpenGL code isn't much different from c++.

Share this post


Link to post
Share on other sites
Specific differences between the 4 items you mentioned.

Immediate mode is fine for rapid prototyping and experimental work. It [i]can[/i] be fine for learning, provided you recognise and accept that it's a suboptimal path that can lead you into bad habits, and that you plan to move away from it as quickly as possible. It's suboptimal for a number of reasons - more calls into the driver means significantly higher function call overhead, and modern drivers are likely to emulate it via a dynamic VBO behind the scenes - not a good idea if the data is not dynamic. It also involves transfer of a lot of data from system memory to the GPU, which again is not good for data that is not dynamic in nature. It's been deprecated from recent GL versions so you need to be aware that you're learning something of very limited future utility.

Display lists provide a mechanism for caching GL commands and data on the driver for subsequent future use. The driver may cache them in GPU memory or in system memory (you have no control over this) and there are a set of highly complex rules for what state gets cached and in what circumstances it happens. In the right cases and with the right hardware it can be the fastest method available, but not all drivers or hardware are equal. Once created you can't modify a display list - you can only execute it or destroy it. If state or data needs to change you're SoL. Display lists are also deprecated so clean interaction with current and future GL functionality may not be guaranteed in all cases - approach with extreme caution in other words.

Vertex arrays allow you to specify a vertex layout and data in system memory in a handful of calls, and transfer it to the GPU very quickly in a single call. This retains the immediate mode overhead of needing to transfer data that may not change every time, but removes the function call overhead. For older code or code that needs to be compatible with older drivers (and note that we're talking [i]much[/i] older here - in the order of 10 years or so) this should be the preferred option. These are also deprecated, but - since VBOs are built on top of vertex arrays - are more likely to work well with modern OpenGL (e.g. instancing works perfectly fine with vertex arrays).

VBOs are the modern OpenGL way of doing everything. They're built on top of vertex arrays so they share the advantage of needing very few calls to specify and draw geometry, and have the added advantage that the data [i]may[/i] be stored in memory that is more optimal for the driver. This suits static data perfectly, but does mean that you need to be slightly more careful about how you operate with VBOs if you're using dynamic data (although do note that using shaders as well means that much data which formerly needed to be dynamic does not necessarily need to be so any more). As a general rule VBOs should be fastest of all on the widest range of hardware, but do note that it's [i]incredibly[/i] easy to write code using VBOs that runs slower than anything else if you're sloppy or careless.

With all that in mind my recommendation is to use vertex arrays for learning, but keep an eye on moving to VBOs. The reason why is that vertex arrays can share a lot of the same coding style as VBOs so you're primed for an easier move, but avoid traps for the unwary that can cause pipeline stalls throughout your program. Vertex arrays have also been available since OpenGL 1.1 so you can be very confident that driver support is ubiquitous. The same applies to VBOs, of course (although it's 1.5 rather than 1.1). So vertex arrays first and - when you get comfortable with them and build up more understanding of how things work in general - switch to VBOs.

Share this post


Link to post
Share on other sites
@mhagain:
Thanks for the detailed explanation. But after searching OpenGL's wiki I found the [url="http://www.opengl.org/wiki/Vertex_Buffer_Object"]Vertex Buffer Object page[/url].


Unfortunatly the following is written:
[quote]Legacy Note: Versions of OpenGL prior to 3.0 allowed the use of client-side data for vertex rendering, but GL 3.0 deprecated this. Core GL 3.1 and greater forbid client-side vertex data, so VBOs are the only means for rendering.[/quote]

And they state offcourse that it is recommended that we do not use any of these functionality in our programs.

So I have a two questions about this:[list=1]
[*]What is the meaning of Legacy? as 'lardpensjo' stated.
[*]What do they mean by client-side data? Isn't everything client sided?
[/list]

Share this post


Link to post
Share on other sites
[quote name='goowik' timestamp='1341341075' post='4955397']
So I have a two questions about this:[list=1]
[*]What is the meaning of Legacy? as 'lardpensjo' stated.
[*]What do they mean by client-side data? Isn't everything client sided?
[/list]
[/quote]
Legacy refers to the old OpenGL API up to version 2.1. Much of OpenGL 2.1 was removed from the API when 3.0 was introduced (there was a combatibility mode for some versions, but that compatiblity mode has been removed as well in 3.3), incluiding things such as display lists and client-side vertex arrays. Legacy refers to the now-deprecated API of version 2.1 and earlier.

Client-side and server-side in this context refers to the application (the client) and the OpenGL implementation/driver (the server). These are typically on the same computer (you run the application on the same computer you have your graphics card on), but that does not have to be the case. Especially on unix-platforms and their windowing systems, you can basically have the application run on one computer and have the display on another computer.

Client-side data in this context means the data is stored in memory managed by the application. For example, when you allocate the memory with malloc or new, or store the data in an std::vector). Server-side data means that the data is stored in memory managed by OpenGL. For example, texture data stored in a texture object with glTexImage or vertex arrays stored in a VBO are both stored in memory managed by OpenGL. They don't have to be physically stored on the graphics card, only that the memory is managed by OpenGL.

Server-side data is the only way to store any data in modern OpenGL. You may have to load your vertex arrays into your own memory before uploading them to your buffer objects of course, but you cannot use the vexrtex arrays to draw something until it has been uploaded into VBOs. Server-side is mandatory for everything involving user data at the moment, not just vertex arrays.

Share this post


Link to post
Share on other sites
If you have the choice, consider the API that is geared for the future of OpenGL. On mobile devices that would be OpenGL ES 2.0. Even if OpenGL 4.2 still supports the legacy api, you should try to avoid it if you can...
That being said, using immediate mode is still ok for quick testing and learning. But for the long run, and production code, avoid legacy API.
This page has some info about OpenGL Core profile: http://www.opengl.org/wiki/Core_And_Compatibility_in_Contexts

Look for glCullFace to find out how you can cull the invisible faces of your cube. glCullFace will always work no matter the rendering API you use.

Share this post


Link to post
Share on other sites
@Brother Bob:
Okay now I get it! So most of the code is backwards compatible till OpenGL 3.0.
Just out of curiosity, client/server side is this applicable to most graphic libraries (such as directX)?

@CodedVentures:
K so that clears most of it. To recap you simply have 2 "packages" (if I may call it this way):[list]
[*]The Core package
[*]The Compatibility (which was introduced in 3.2)
[/list]
Will the core always be the same? As all deprecated methods were removed?


EDIT:
I also was looking for a decent book to buy/rent and came across the "[i][b]OpenGL Superbible[/b][/i]"
But on [url="http://www.amazon.com/OpenGL-SuperBible-Comprehensive-Tutorial-Reference/dp/0321712617"]Amazon[/url] it does seem to have a low score (3.5/5) and the reviews are very various. Edited by goowik

Share this post


Link to post
Share on other sites
[quote name='goowik' timestamp='1341384981' post='4955542']
@Brother Bob:
Okay now I get it! So most of the code is backwards compatible till OpenGL 3.0.
[/quote]
That is correct. The compatibility mode of the modern API lets you extent the backward compatibility of the legacy API to version 3.1 even.

The modern API is mostly backward compatible as well, although there are some changes that makes it not. For example, vertex array objects (VAO) are not required in version 3, but are in version 4. That means that you cannot run a version 3 compatible program on a version 4 context. But that change is trivial; just use VAO in version 3 as well and you will have no problems with version 4.

[quote name='goowik' timestamp='1341384981' post='4955542']
Just out of curiosity, client/server side is this applicable to most graphic libraries (such as directX)?
[/quote]
I have no idea whether Direct3D makes the difference explicit in some way or not. I would, however, guess that pretty much the same requirements on memory management applies to both Direct3D and OpenGL: manual memory management is not possible, you have to let the API handle your resources.

[quote name='goowik' timestamp='1341384981' post='4955542']
@CodedVentures:
K so that clears most of it. To recap you simply have 2 "packages" (if I may call it this way):[list]
[*]The Core package
[*]The Compatibility (which was introduced in 3.2)
[/list]
Will the core always be the same? As all deprecated methods were removed?
[/quote]
The core changes, but (with few exceptions, see for example my comment above on VAO in version 3 and 4) new stuff are only added. What works on an earlier version typically works on a later version as well. Only exception of course is the major change from the legacy API to the modern API.

The compatibility mode was introduced in 3.0 though. From version 3.2 and onwards, compatibility mode is not available. Thus, it is only available for the modern API for versions 3.0 and 3.1.

Share this post


Link to post
Share on other sites
[quote name='goowik' timestamp='1341384981' post='4955542']
I also was looking for a decent book to buy/rent and came across the "OpenGL Superbible"
But on Amazon it does seem to have a low score (3.5/5) and the reviews are very various.
[/quote]
I have that book, and I think the weakness is that it is that the examples are based on a home made support library. The disadvantage of that is for beginners, that do want simple examples where you can see the whole solution on the same page. The advantage is for the intermediate or advanced reader, that no longer cares about the basics but want to learn and understand advanced concepts.

If you have understood the basics, then the book is excellent.

Actually, a member of the forum, [url="http://www.gamedev.net/user/158805-japro/"]japro[/url], recently created basic minimal examples, perfect for beginners to start with. See [url="https://github.com/progschj/OpenGL-Examples"]https://github.com/progschj/OpenGL-Examples[/url].

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
      628294
    • Total Posts
      2981882
  • 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