Jump to content
  • Advertisement
Sign in to follow this  
bkt

OpenGL Designing a Renderer

This topic is 4433 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

I've spent a lot of time thinking about different ways to design a renderer. I've looked at a lot of examples, and have a few books lying around the house as well. But alas, I have a few questions, and I just would like to basically have them clarified. What's better than coming here to ask the questions? I'm still trying to grasp the difference between Fixed Function Pipeline and Programmable Pipeline. I think most of the tutorials I have seen (in books and online) have been examples of programmable pipelines, but I really don't know the difference. I know that programmable pipelines include Shaders, but I am sure that is not the only difference, right? I am also rather sure that the OpenGL tutorials that NeHe has are all Fixed Function? If there are any good books that illstrate the difference I would be glad to know of them! I've been searching Amazon for a few, and it seems this one seems pretty relevant to what I am looking for. What's the most efficient way to design a renderer and have it expandable? I am guessing that something like the following?:
HandleMessage();

Clear();
BeginFrame();
For All->Draw();
EndFrame();

Events();
Input();

Thanks a lot everyone!

Share this post


Link to post
Share on other sites
Advertisement
Ok, a quick explanation would be, a fixed function pipeline has a bunch of fixed functions (wow really?! :-p) that you can configure and then the vert data is pushed through those functions. With a programmable pipeline instead of just pushing it through the fixed hardware functions, you can set programs (shaders) that the verts will be pushed through (i.e.: the program will run on each vert) this is for vertex shaders. Further down the pipeline the pixel/fragment shader will run on all the fragments that were generated for the given frame, again instead of just going through the standard texturing hardware functions, a program is run on each fragment (a pixel/fragment shader).

If you looking to learn Shader programming I'd recommend "The Cg Tutorial", tho this doesn't explain how to architect a renderer or engine to encapsulate the programmable pipeline. Infact it doesn't even deal with the Cg run-time thats left as an exercise for the reader.

With regard to your post about designing a renderer, the way you say is basically how most renderers work, i.e.: they have a list of stuff to draw and they run through it and draw it. You have to supply a renderer with everything its going to need to draw the given primitive, i.e.: vert data, textures, shaders, whatever. Of course there are ways to make the renderer more efficient, for instance, grouping those primitives that make use of the same shader program or materials, so your not constantly binding and unbinding the same shaders to the video card, same goes for material properties, although i wouldn't worry about material sorting until you've got something up and running.

NeHe stuff is all fixed function yes, unless he explicitly mentions using Shader programs which I believe he does around lesson 45 IIRC? As for books, check out:

(the afore mentioned) The Cg Tutorial - Randima Fernando & Mark J. Kilgard
ShaderX - Wolfgang Engel
3D Engine Architecture - David H. Elberly

The first 2 will give you a decent grounding in shader programming, and the last gives you an idea of what it takes to architect a well structured and extendible multi-API renderer.

Once you get a renderer up and running, your probrably going to want to look into some scene management to cut down what your actually sending to the renderer for drawing (no point attempting to draw things you can't see right?) so you'll want to check out scenegraphs, frustum culling, occlusion culling, oct-trees, BSP (althought typically not used much for rendering more for collisions these days), all that stuff.

Hope this helps ;-)

Share this post


Link to post
Share on other sites
Ill try to add my knowlege.

As this is the renderer, it should only render, right?
So all transformations and stuff are already calculated?
If not, you need a parent object to transform the matrix before you draw the child objct (if you got any)...

The next thing is sorting. Objects with the same texture / shader should be drawed in order to reduce texture / shader switching... (might not be an issue if not to heavy graphics).

Who is responsible for deciding if an object is visible? If its behind the camera, the renderer could do this, but if its for example inside a box, or to far away, you should not try to render it (and rely on that the distance cap removes them).

What i heard people do it that the renderer infact is only a smart queue!
When your logic decides that an object should be rendered, it passes the object to a rendering queue, witch you can flush at the end of the frame.

This is great because then your renderer is independant of your scenegraph structure, and objects can be sorted when they are added to the queue.
If you need z sorting (witch is good when doing pixel shaders (draw closest first) or if you want transparency) you can easely modify the order of your rendering whitout affecting any other part of the system. You could also have flags like: IS_SHADOW(draw me last) or IS_EFFECT(draw me even later)

The drawback is that you cant use matrix push and pop directly with this approach (that is if you have "child" objects), so you need to calculate the transformation of the object, and then add the saved transformation matrix with the object to the renderqueue. This might give some overhead if thousands of objects...

So now you have a encapsulated renderer with the simple interface:

-enqueue(object,flag)
-flush()

totaly separated from your logics and scenegraph...
it takes care of order and optimalisation by itselfe, and this is hidden from the rest of the system.

-long post

-anders

Share this post


Link to post
Share on other sites
Its quite common for the algorithm requesting objects to be rendered to be able to trivialy iterate through geometry with common materials .. such as iterating through all the grass blades in the scene.

It would be wasteful to change the problem to something less trivial under the banner of being 'generic'


Some geometry will be part of a "set" .. in such cases, its the SET which should have a render method in order to take advantage of the priori knowledge of common materials.

Other geometry will NOT be part of a "set" in the sense of common materials even though they may be part of a set. For instance, the set of all agents in the world. Each has a dynamic model. It is ONLY these sets here that really should have the whole queue-it-up-and-sort-by-material strategy.

So I believe that the overall design of the rendering system should be capable of both queing up render requests AS WELL AS exposing API specific features that allow the caller to directly leverage batching on its own in those cases where its obvious that a generic queue system is sub-optimal.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Popular Now

  • Advertisement
  • Similar Content

    • By LukasBanana
      Hi all,
       
      I'm trying to generate MIP-maps of a 2D-array texture, but only a limited amount of array layers and MIP-levels.
      For instance, to generate only the first 3 MIP-maps of a single array layer of a large 2D-array.
       
      After experimenting with glBlitFramebuffer to generate the MIP-maps manually but still with some sort of hardware acceleration,
      I ended up with glTextureView which already works with the limited amount of array layers (I can also verify the result in RenderDoc).
      However, glGenerateMipmap (or glGenerateTextureMipmap) always generates the entire MIP-chain for the specified array layer.
       
      Thus, the <numlevels> parameter of glTextureView seems to be ignored in the MIP-map generation process.
      I also tried to use glTexParameteri(..., GL_TEXTURE_MAX_LEVEL, 3), but this has the same result.
      Can anyone explain me how to solve this?
       
      Here is an example code, how I do it:
      void GenerateSubMips( GLuint texID, GLenum texTarget, GLenum internalFormat, GLuint baseMipLevel, GLuint numMipLevels, GLuint baseArrayLayer, GLuint numArrayLayers) { GLuint texViewID = 0; glGenTextures(1, &texViewID); glTextureView( texViewID, texTarget, texID, internalFormat, baseMipLevel, numMipLevels, baseArrayLayer, numArrayLayers ); glGenerateTextureMipmap(texViewID); glDeleteTextures(1, &texViewID); } GenerateSubMips( myTex, GL_TEXTURE_2D_ARRAY, GL_RGBA8, 0, 3, // only the first 3 MIP-maps 4, 1 // only one array layer with index 4 );  
      Thanks and kind regards,
      Lukas
    • By mmmax3d
      Hi everyone,
      I would need some assistance from anyone who has a similar experience
      or a nice idea!
      I have created a skybox (as cube) and now I need to add a floor/ground.
      The skybox is created from cubemap and initially it was infinite.
      Now it is finite with a specific size. The floor is a quad in the middle
      of the skybox, like a horizon.
      I have two problems:
      When moving the skybox upwards or downwards, I need to
      sample from points even above the horizon while sampling
      from the botton at the same time.  I am trying to create a seamless blending of the texture
      at the points of the horizon, when the quad is connected
      to the skybox. However, I get skew effects. Does anybody has done sth similar?
      Is there any good practice?
      Thanks everyone!
    • By mmmax3d
      Hi everyone,
      I would need some assistance from anyone who has a similar experience
      or a nice idea!
      I have created a skybox (as cube) and now I need to add a floor/ground.
      The skybox is created from cubemap and initially it was infinite.
      Now it is finite with a specific size. The floor is a quad in the middle
      of the skybox, like a horizon.
      I have two problems:
      When moving the skybox upwards or downwards, I need to
      sample from points even above the horizon while sampling
      from the botton at the same time.  I am trying to create a seamless blending of the texture
      at the points of the horizon, when the quad is connected
      to the skybox. However, I get skew effects. Does anybody has done sth similar?
      Is there any good practice?
      Thanks everyone!
    • By iArtist93
      I'm trying to implement PBR into my simple OpenGL renderer and trying to use multiple lighting passes, I'm using one pass per light for rendering as follow:
      1- First pass = depth
      2- Second pass = ambient
      3- [3 .. n] for all the lights in the scene.
      I'm using the blending function glBlendFunc(GL_ONE, GL_ONE) for passes [3..n], and i'm doing a Gamma Correction at the end of each fragment shader.
      But i still have a problem with the output image it just looks noisy specially when i'm using texture maps.
      Is there anything wrong with those steps or is there any improvement to this process?
    • By babaliaris
      Hello Everyone!
      I'm learning openGL, and currently i'm making a simple 2D game engine to test what I've learn so far.  In order to not say to much, i made a video in which i'm showing you the behavior of the rendering.
      Video: 
       
      What i was expecting to happen, was the player moving around. When i render only the player, he moves as i would expect. When i add a second Sprite object, instead of the Player, this new sprite object is moving and finally if i add a third Sprite object the third one is moving. And the weird think is that i'm transforming the Vertices of the Player so why the transformation is being applied somewhere else?
       
      Take a look at my code:
      Sprite Class
      (You mostly need to see the Constructor, the Render Method and the Move Method)
      #include "Brain.h" #include <glm/gtc/matrix_transform.hpp> #include <vector> struct Sprite::Implementation { //Position. struct pos pos; //Tag. std::string tag; //Texture. Texture *texture; //Model matrix. glm::mat4 model; //Vertex Array Object. VertexArray *vao; //Vertex Buffer Object. VertexBuffer *vbo; //Layout. VertexBufferLayout *layout; //Index Buffer Object. IndexBuffer *ibo; //Shader. Shader *program; //Brains. std::vector<Brain *> brains; //Deconstructor. ~Implementation(); }; Sprite::Sprite(std::string image_path, std::string tag, float x, float y) { //Create Pointer To Implementaion. m_Impl = new Implementation(); //Set the Position of the Sprite object. m_Impl->pos.x = x; m_Impl->pos.y = y; //Set the tag. m_Impl->tag = tag; //Create The Texture. m_Impl->texture = new Texture(image_path); //Initialize the model Matrix. m_Impl->model = glm::mat4(1.0f); //Get the Width and the Height of the Texture. int width = m_Impl->texture->GetWidth(); int height = m_Impl->texture->GetHeight(); //Create the Verticies. float verticies[] = { //Positions //Texture Coordinates. x, y, 0.0f, 0.0f, x + width, y, 1.0f, 0.0f, x + width, y + height, 1.0f, 1.0f, x, y + height, 0.0f, 1.0f }; //Create the Indicies. unsigned int indicies[] = { 0, 1, 2, 2, 3, 0 }; //Create Vertex Array. m_Impl->vao = new VertexArray(); //Create the Vertex Buffer. m_Impl->vbo = new VertexBuffer((void *)verticies, sizeof(verticies)); //Create The Layout. m_Impl->layout = new VertexBufferLayout(); m_Impl->layout->PushFloat(2); m_Impl->layout->PushFloat(2); m_Impl->vao->AddBuffer(m_Impl->vbo, m_Impl->layout); //Create the Index Buffer. m_Impl->ibo = new IndexBuffer(indicies, 6); //Create the new shader. m_Impl->program = new Shader("Shaders/SpriteShader.shader"); } //Render. void Sprite::Render(Window * window) { //Create the projection Matrix based on the current window width and height. glm::mat4 proj = glm::ortho(0.0f, (float)window->GetWidth(), 0.0f, (float)window->GetHeight(), -1.0f, 1.0f); //Set the MVP Uniform. m_Impl->program->setUniformMat4f("u_MVP", proj * m_Impl->model); //Run All The Brains (Scripts) of this game object (sprite). for (unsigned int i = 0; i < m_Impl->brains.size(); i++) { //Get Current Brain. Brain *brain = m_Impl->brains[i]; //Call the start function only once! if (brain->GetStart()) { brain->SetStart(false); brain->Start(); } //Call the update function every frame. brain->Update(); } //Render. window->GetRenderer()->Draw(m_Impl->vao, m_Impl->ibo, m_Impl->texture, m_Impl->program); } void Sprite::Move(float speed, bool left, bool right, bool up, bool down) { if (left) { m_Impl->pos.x -= speed; m_Impl->model = glm::translate(m_Impl->model, glm::vec3(-speed, 0, 0)); } if (right) { m_Impl->pos.x += speed; m_Impl->model = glm::translate(m_Impl->model, glm::vec3(speed, 0, 0)); } if (up) { m_Impl->pos.y += speed; m_Impl->model = glm::translate(m_Impl->model, glm::vec3(0, speed, 0)); } if (down) { m_Impl->pos.y -= speed; m_Impl->model = glm::translate(m_Impl->model, glm::vec3(0, -speed, 0)); } } void Sprite::AddBrain(Brain * brain) { //Push back the brain object. m_Impl->brains.push_back(brain); } pos *Sprite::GetPos() { return &m_Impl->pos; } std::string Sprite::GetTag() { return m_Impl->tag; } int Sprite::GetWidth() { return m_Impl->texture->GetWidth(); } int Sprite::GetHeight() { return m_Impl->texture->GetHeight(); } Sprite::~Sprite() { delete m_Impl; } //Implementation Deconstructor. Sprite::Implementation::~Implementation() { delete texture; delete vao; delete vbo; delete layout; delete ibo; delete program; }  
      Renderer Class
      #include "Renderer.h" #include "Error.h" Renderer::Renderer() { } Renderer::~Renderer() { } void Renderer::Draw(VertexArray * vao, IndexBuffer * ibo, Texture *texture, Shader * program) { vao->Bind(); ibo->Bind(); program->Bind(); if (texture != NULL) texture->Bind(); GLCall(glDrawElements(GL_TRIANGLES, ibo->GetCount(), GL_UNSIGNED_INT, NULL)); } void Renderer::Clear(float r, float g, float b) { GLCall(glClearColor(r, g, b, 1.0)); GLCall(glClear(GL_COLOR_BUFFER_BIT)); } void Renderer::Update(GLFWwindow *window) { /* Swap front and back buffers */ glfwSwapBuffers(window); /* Poll for and process events */ glfwPollEvents(); }  
      Shader Code
      #shader vertex #version 330 core layout(location = 0) in vec4 aPos; layout(location = 1) in vec2 aTexCoord; out vec2 t_TexCoord; uniform mat4 u_MVP; void main() { gl_Position = u_MVP * aPos; t_TexCoord = aTexCoord; } #shader fragment #version 330 core out vec4 aColor; in vec2 t_TexCoord; uniform sampler2D u_Texture; void main() { aColor = texture(u_Texture, t_TexCoord); } Also i'm pretty sure that every time i'm hitting the up, down, left and right arrows on the keyboard, i'm changing the model Matrix of the Player and not the others.
       
      Window Class:
      #include "Window.h" #include <GL/glew.h> #include <GLFW/glfw3.h> #include "Error.h" #include "Renderer.h" #include "Scene.h" #include "Input.h" //Global Variables. int screen_width, screen_height; //On Window Resize. void OnWindowResize(GLFWwindow *window, int width, int height); //Implementation Structure. struct Window::Implementation { //GLFW Window. GLFWwindow *GLFW_window; //Renderer. Renderer *renderer; //Delta Time. double delta_time; //Frames Per Second. int fps; //Scene. Scene *scnene; //Input. Input *input; //Deconstructor. ~Implementation(); }; //Window Constructor. Window::Window(std::string title, int width, int height) { //Initializing width and height. screen_width = width; screen_height = height; //Create Pointer To Implementation. m_Impl = new Implementation(); //Try initializing GLFW. if (!glfwInit()) { std::cout << "GLFW could not be initialized!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); exit(-1); } //Setting up OpenGL Version 3.3 Core Profile. glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); /* Create a windowed mode window and its OpenGL context */ m_Impl->GLFW_window = glfwCreateWindow(width, height, title.c_str(), NULL, NULL); if (!m_Impl->GLFW_window) { std::cout << "GLFW could not create a window!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); glfwTerminate(); exit(-1); } /* Make the window's context current */ glfwMakeContextCurrent(m_Impl->GLFW_window); //Initialize GLEW. if(glewInit() != GLEW_OK) { std::cout << "GLEW could not be initialized!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); glfwTerminate(); exit(-1); } //Enabling Blending. GLCall(glEnable(GL_BLEND)); GLCall(glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)); //Setting the ViewPort. GLCall(glViewport(0, 0, width, height)); //**********Initializing Implementation**********// m_Impl->renderer = new Renderer(); m_Impl->delta_time = 0.0; m_Impl->fps = 0; m_Impl->input = new Input(this); //**********Initializing Implementation**********// //Set Frame Buffer Size Callback. glfwSetFramebufferSizeCallback(m_Impl->GLFW_window, OnWindowResize); } //Window Deconstructor. Window::~Window() { delete m_Impl; } //Window Main Loop. void Window::MainLoop() { //Time Variables. double start_time = 0, end_time = 0, old_time = 0, total_time = 0; //Frames Counter. int frames = 0; /* Loop until the user closes the window */ while (!glfwWindowShouldClose(m_Impl->GLFW_window)) { old_time = start_time; //Total time of previous frame. start_time = glfwGetTime(); //Current frame start time. //Calculate the Delta Time. m_Impl->delta_time = start_time - old_time; //Get Frames Per Second. if (total_time >= 1) { m_Impl->fps = frames; total_time = 0; frames = 0; } //Clearing The Screen. m_Impl->renderer->Clear(0, 0, 0); //Render The Scene. if (m_Impl->scnene != NULL) m_Impl->scnene->Render(this); //Updating the Screen. m_Impl->renderer->Update(m_Impl->GLFW_window); //Increasing frames counter. frames++; //End Time. end_time = glfwGetTime(); //Total time after the frame completed. total_time += end_time - start_time; } //Terminate GLFW. glfwTerminate(); } //Load Scene. void Window::LoadScene(Scene * scene) { //Set the scene. m_Impl->scnene = scene; } //Get Delta Time. double Window::GetDeltaTime() { return m_Impl->delta_time; } //Get FPS. int Window::GetFPS() { return m_Impl->fps; } //Get Width. int Window::GetWidth() { return screen_width; } //Get Height. int Window::GetHeight() { return screen_height; } //Get Input. Input * Window::GetInput() { return m_Impl->input; } Renderer * Window::GetRenderer() { return m_Impl->renderer; } GLFWwindow * Window::GetGLFWindow() { return m_Impl->GLFW_window; } //Implementation Deconstructor. Window::Implementation::~Implementation() { delete renderer; delete input; } //OnWindowResize void OnWindowResize(GLFWwindow *window, int width, int height) { screen_width = width; screen_height = height; //Updating the ViewPort. GLCall(glViewport(0, 0, width, height)); }  
      Brain Class
      #include "Brain.h" #include "Sprite.h" #include "Window.h" struct Brain::Implementation { //Just A Flag. bool started; //Window Pointer. Window *window; //Sprite Pointer. Sprite *sprite; }; Brain::Brain(Window *window, Sprite *sprite) { //Create Pointer To Implementation. m_Impl = new Implementation(); //Initialize Implementation. m_Impl->started = true; m_Impl->window = window; m_Impl->sprite = sprite; } Brain::~Brain() { //Delete Pointer To Implementation. delete m_Impl; } void Brain::Start() { } void Brain::Update() { } Window * Brain::GetWindow() { return m_Impl->window; } Sprite * Brain::GetSprite() { return m_Impl->sprite; } bool Brain::GetStart() { return m_Impl->started; } void Brain::SetStart(bool value) { m_Impl->started = value; } Script Class (Its a Brain Subclass!!!)
      #include "Script.h" Script::Script(Window *window, Sprite *sprite) : Brain(window, sprite) { } Script::~Script() { } void Script::Start() { std::cout << "Game Started!" << std::endl; } void Script::Update() { Input *input = this->GetWindow()->GetInput(); Sprite *sp = this->GetSprite(); //Move this sprite. this->GetSprite()->Move(200 * this->GetWindow()->GetDeltaTime(), input->GetKeyDown("left"), input->GetKeyDown("right"), input->GetKeyDown("up"), input->GetKeyDown("down")); std::cout << sp->GetTag().c_str() << ".x = " << sp->GetPos()->x << ", " << sp->GetTag().c_str() << ".y = " << sp->GetPos()->y << std::endl; }  
      Main:
      #include "SpaceShooterEngine.h" #include "Script.h" int main() { Window w("title", 600,600); Scene *scene = new Scene(); Sprite *player = new Sprite("Resources/Images/player.png", "Player", 100,100); Sprite *other = new Sprite("Resources/Images/cherno.png", "Other", 400, 100); Sprite *other2 = new Sprite("Resources/Images/cherno.png", "Other", 300, 400); Brain *brain = new Script(&w, player); player->AddBrain(brain); scene->AddSprite(player); scene->AddSprite(other); scene->AddSprite(other2); w.LoadScene(scene); w.MainLoop(); return 0; }  
       
      I literally can't find what is wrong. If you need more code, ask me to post it. I will also attach all the source files.
      Brain.cpp
      Error.cpp
      IndexBuffer.cpp
      Input.cpp
      Renderer.cpp
      Scene.cpp
      Shader.cpp
      Sprite.cpp
      Texture.cpp
      VertexArray.cpp
      VertexBuffer.cpp
      VertexBufferLayout.cpp
      Window.cpp
      Brain.h
      Error.h
      IndexBuffer.h
      Input.h
      Renderer.h
      Scene.h
      Shader.h
      SpaceShooterEngine.h
      Sprite.h
      Texture.h
      VertexArray.h
      VertexBuffer.h
      VertexBufferLayout.h
      Window.h
  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

Participate in the game development conversation and more when you create an account on GameDev.net!

Sign me up!