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detlion1643

OpenGL matrix/coordinates?

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To preface, I am using OpenTK and C#. However, I don't think that deters the issue from being something simple to how I am calling OpenGL methods. I don't understand some of the setup stuff, it's mostly pieced together code from other examples until I found something that worked somewhat.

 

Here is my routine for setting up OpenGL:

public bool Initialize(IntPtr Handle, Size ScreenSize)
        {
            //stuff to set in case of GDI
            handle = Handle;
            screensize = ScreenSize;
            bmp = new System.Drawing.Bitmap (screensize.Width, screensize.Height);

            //setup the initial scales
            if ((screensize.Width != 1000) && (screensize.Height != 600))
            {
                scalewidth = 1000 / screensize.Width;
                scaleheight = 600 / screensize.Height;
            }

            if (OpenTK.Configuration.RunningOnAndroid) 
            {
                //
                return true;
            } 
            else 
            {
                //video card name
                glRenderer = GL.GetString (StringName.Renderer);
                //what version of OpenGL do we have?
                glVersionStr = GL.GetString (StringName.Version);
                if (glVersionStr.Length < 3)
                    return false;

                glVersion = new Version (int.Parse (GLVersionStr [0].ToString ()), int.Parse (GLVersionStr [2].ToString ()));
                //glVersion = new Version (int.Parse (glVersionStr [0].ToString()), int.Parse (glVersionStr [2]).ToString());
                // Set viewport
                if (GLFunctions.Viewport (glVersion))
                    GL.Viewport (0, 0, screensize.Width, screensize.Height);
                else
                    return false; //can't use a viewport, default to GDI

                //we now have successfull OpenGL window/context we can use
                // Set rendering options
                GL.MatrixMode (MatrixMode.Projection);

                    GL.Enable (EnableCap.LineSmooth);
                    GL.Enable (EnableCap.PointSmooth);

                    GL.Hint (HintTarget.LineSmoothHint, HintMode.Nicest);
                    GL.Hint (HintTarget.PointSmoothHint, HintMode.Nicest);
                    GL.Hint (HintTarget.PolygonSmoothHint, HintMode.Nicest);
                    GL.Hint (HintTarget.PerspectiveCorrectionHint, HintMode.Nicest);

                // Shading
                    GL.ShadeModel(ShadingModel.Smooth);

                // 3D options
                GL.CullFace(CullFaceMode.Front);
                GL.Enable(EnableCap.Multisample);
                GL.Enable(EnableCap.CullFace);

                // Enable blending
                GL.Enable(EnableCap.Blend);
                GL.BlendFunc(BlendingFactorSrc.SrcAlpha, BlendingFactorDest.OneMinusSrcAlpha);
 
                //without the next two lines we can't see anything
                ProjectionSet(Vector3d.Zero);
                ModelView_Set(Vector3d.Zero, Vector3d.Zero, Vector3d.Zero, 0, true);

                return true;
            }
        }

        private void ProjectionSet(Vector3d renderLocation)
        {
            // Create a perspective frustrum
            Matrix4d projection = Matrix4d.CreatePerspectiveFieldOfView(MathHelper.DegreesToRadians(45), 1000.0 / 600.0, 1.0, 2000.0);

            if (renderLocation != Vector3d.Zero)
            {
                // Move zero point for rendering to upper left corner
                projection *= Matrix4d.CreateTranslation(-1, 1, 0);

                // Translate rendering point to the specified location
                projection *= Matrix4d.CreateTranslation(_3D_ProjectionSpace_NormalizeVector(new Vector3d(renderLocation.X, renderLocation.Y, 0)));
            }

            // Load matrix
            GL.MatrixMode(MatrixMode.Projection);
            GL.LoadIdentity();
            GL.LoadMatrix(ref projection);
        }
        
        public void ModelView_Set(Vector3d cameraLocation, Vector3d cameraRotation, Vector3d cameraOffset, double zoom, bool activateMatrix)
        {
            // Rotate world to get the correct axes in 3D (X going right, Y going down)
            modelview = Matrix4d.CreateRotationZ(MathHelper.DegreesToRadians(180));

            // Rotate camera
            modelview *= Matrix4d.CreateRotationX(MathHelper.DegreesToRadians(cameraRotation.X));
            modelview *= Matrix4d.CreateRotationY(MathHelper.DegreesToRadians(cameraRotation.Y));
            modelview *= Matrix4d.CreateRotationZ(MathHelper.DegreesToRadians(cameraRotation.Z));

            // Offset camera
            modelview *= Matrix4d.CreateTranslation(cameraOffset);

            // Zoom 
            if (zoom != 0)
                modelview *= Matrix4d.Scale(zoom);

            // Set camera with fixed zoom to make the 1000x600 frame match the 1000x600 pixels
            modelview *= Matrix4d.LookAt(new Vector3d(-cameraLocation.X, -cameraLocation.Y, cameraLocation.Z + (-724)), Vector3d.UnitZ, Vector3d.UnitY);

            // Load matrix
            if (activateMatrix)
                ModelView_Activate();
        }

        /// <summary>
        /// Activates the model view
        /// </summary>
        public void ModelView_Activate()
        {
            GL.MatrixMode(MatrixMode.Modelview);
            GL.LoadIdentity();
            GL.LoadMatrix(ref modelview);
        }

Now, I create a bitmap with the text to be drawn to the screen. Then I create a texture and bind it OpenGL. I then go to display that texture which semi works:

private void DrawImage(Image image, int X, int Y, int Z, int Width, int Height)
        {

            GL.Enable(EnableCap.Texture2D);
            if (image.GenerateTexture)
            {
                if (!LoadTexture (image))
                {
                    GL.Disable (EnableCap.Texture2D);
                    return;
                }
            }

            // Save current matrix
            //GL.PushMatrix();
                      
            //forget the values I passed and use hardcoded for testing
            GL.Color4(1F, 1F, 1F, 1F);
            GL.BindTexture (TextureTarget.Texture2D, image.Texture);
            GL.Begin(PrimitiveType.Quads);
            GL.TexCoord2(0.0f, 0.0f); 
            GL.Vertex3(0, 0, 0); //TOP-LEFT
            GL.TexCoord2(1.0f, 0.0f); 
            GL.Vertex3(1000, 0, 0); //TOP-RIGHT
            GL.TexCoord2(1.0f, 1.0f); 
            GL.Vertex3(1000, 300, 0); //BOTTOM-RIGHT
            GL.TexCoord2(0.0f, 1.0f); 
            GL.Vertex3(0, 300, 0); //BOTTOM-LEFT
            GL.End();

            // Restore matrix
            //GL.PopMatrix();

        }

As you can see, the GL.Vertex3 calls are outside the range of -1 to 1. For some reason this is how I can display the texture. However it shows up in the bottom right quadrant of the screen. Changing the Vertex3's x axis to anything negative (thinking -1 would be left of screen/view) completely hides the texture. Subtle trials like -0.1 don't change the location either.

 

This should be at Top left, 1000 wide, 300 down. I can't seem to figure this out...

[attachment=23844:opengl.png]

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I don't understand some of the setup stuff, it's mostly pieced together code from other examples until I found something that worked somewhat.

Stop here, delete your project, look for tutorials and start over again. This time concentrate on understanding the stuff you are using and why it does/doesn't works this way. tongue.png

 

It is the most safe and eventually quickest way to get into something new. Building your project on something which magically works sometimes, without knowing why it works at all huh.png .. will often end at the point , where you can't figure out a show-stopper (a bug, which ruins your whole project).

 

My first really big project ended this way, it was a pretty cool learning experience, still it hurts a lot if you consider the progress made sad.png .

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I went ahead and stripped everything down. I then followed some examples and tutorials and have some triangles rendering to the screen.

 

I am calling this to Initialize OpenGL:

GL.Viewport (0, 0, screensize.Width, screensize.Height);
                GL.Enable(EnableCap.DepthTest);
                GL.Enable(EnableCap.Texture2D);

                Matrix4 modelview = Matrix4.LookAt(Vector3.Zero, Vector3.UnitZ, Vector3.UnitY);
                GL.MatrixMode(MatrixMode.Modelview);
                GL.LoadMatrix(ref modelview);

I am then testing this by drawing a large triangle, then a small one

//large
            GL.Color4 (System.Drawing.Color.Yellow);
            GL.Begin(PrimitiveType.Triangles);
            GL.Vertex3(-1.0f, -1.0f, 4.0f);
            GL.Vertex3(1.0f, -1.0f, 4.0f);
            GL.Vertex3(0.0f, 1.0f, 4.0f);
            GL.End();

            //small
            GL.Color4 (System.Drawing.Color.Blue);
            GL.Begin(PrimitiveType.Triangles);
            GL.Vertex3(0.5f, -0.5f, 4.0f); //bottom left
            GL.Vertex3(0.0f, 1.0f, 4.0f); //top
            GL.Vertex3(-0.5f, -0.5f, 4.0f); //bottom right
            GL.End();

but only the large one is drawn (the small should be drawn on top of the large). If I move the "small" triangle code above the large, I see both triangles. Is the rendering/drawing order reversed for OpenGL or is it something I did wrong?

 

EDIT: Turns out I was a little hasty with my clicking. This is because of the

GL.Enable(EnableCap.DepthTest);
I thought depth testing was needed in order to use the z-axis for when I need 3d? Edited by detlion1643

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I was merely talking about why the first triangle in code wasn't drawn first, then the second in code drawn on top of the first. Both use the same depth of 4.0.

 

In fact, it seems like the initial -1 -> 1 coordinate system isn't working how I thought it would. Here is code that I trialed and errored to get right:

//negative y = down
            //negative x = right
            //negative z = closer to camera, less than 1 is invisible
            //the following x, y, and z coordinates fill the screen on the initial screensize
            GL.Vertex3( -1.38f, -0.828f, 2.0f);    // bottom right
            GL.Color3 (System.Drawing.Color.Green);
            GL.Vertex3( 1.38f, -0.828f, 2.0f);    // bottom left
            GL.Color3 (System.Drawing.Color.Red);
            GL.Vertex3( 1.38f, 0.828, 2.0f);    // top left
            GL.Color3 (System.Drawing.Color.DarkOrange);
            GL.Vertex3( -1.38f, 0.828f, 2.0f);    // top right
            GL.End ();
I know the depth is 2.0f, but even at 1.0f using -1, 1 for x/y values fill more than the screen (as 0.8 values fill more than the screen, 0.5 fill less than the screen).

 

Here is my resize code:

GL.Viewport(Left, Top, Width, Height);
            //Matrix4 projection = Matrix4.CreatePerspectiveFieldOfView((float)Math.PI / 4, Width / (float)Height, 0.5f, 64.0f);
            Matrix4d projection = Matrix4d.CreatePerspectiveFieldOfView(MathHelper.DegreesToRadians(45), Width / (float)Height, 1.0, 1000.0);
            GL.MatrixMode(MatrixMode.Projection);
            GL.LoadMatrix(ref projection);

 

Should I  be concerned about my starting point. I am going to have to calculate pixel coordinates based on a 1000x600 initial screensize in order to render my controls. For example, a control placed X=0, Y=0, W=500, H=300 would be calculated based on the above starting point. So the left side would be at 1.38f, the right side at 0, the top at 0.828 and the bottom at 0.

 

Doesn't this sound overly complex?

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I skipped over your initial problem. If you are trying to render 2D with openGL  You dont want persepctive (which implies a 3D world) you want orthographic.

 

Matrix4.____Ortho____
Should be a function something like that. Depth will still matter but you can work in 2D. Ortho(0,screenwidth, 0, screenheight)  <-- allows you to call glVertex3f() with 2d pixel coordinates + some z-depth.

 

With Ortho there is no perspective division to warp stuff away from the camera. The z value doesnt effect perspective, the input x,y  will be the output x,y

Edited by dpadam450

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      #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
    • By Cristian Decu
      Hello fellow programmers,
      For a couple of days now i've decided to build my own planet renderer just to see how floating point precision issues
      can be tackled. As you probably imagine, i've quickly faced FPP issues when trying to render absurdly large planets.
       
      I have used the classical quadtree LOD approach;
      I've generated my grids with 33 vertices, (x: -1 to 1, y: -1 to 1, z = 0).
      Each grid is managed by a TerrainNode class that, depending on the side it represents (top, bottom, left right, front, back),
      creates a special rotation-translation matrix that moves and rotates the grid away from the origin so that when i finally
      normalize all the vertices on my vertex shader i can get a perfect sphere.
      T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, 1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(180.0), glm::dvec3(1.0, 0.0, 0.0)); sides[0] = new TerrainNode(1.0, radius, T * R, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_FRONT)); T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, -1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(0.0), glm::dvec3(1.0, 0.0, 0.0)); sides[1] = new TerrainNode(1.0, radius, R * T, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_BACK)); // So on and so forth for the rest of the sides As you can see, for the front side grid, i rotate it 180 degrees to make it face the camera and push it towards the eye;
      the back side is handled almost the same way only that i don't need to rotate it but simply push it away from the eye.
      The same technique is applied for the rest of the faces (obviously, with the proper rotations / translations).
      The matrix that result from the multiplication of R and T (in that particular order) is send to my vertex shader as `r_Grid'.
      // spherify vec3 V = normalize((r_Grid * vec4(r_Vertex, 1.0)).xyz); gl_Position = r_ModelViewProjection * vec4(V, 1.0); The `r_ModelViewProjection' matrix is generated on the CPU in this manner.
      // No the most efficient way, but it works. glm::dmat4 Camera::getMatrix() { // Create the view matrix // Roll, Yaw and Pitch are all quaternions. glm::dmat4 View = glm::toMat4(Roll) * glm::toMat4(Pitch) * glm::toMat4(Yaw); // The model matrix is generated by translating in the oposite direction of the camera. glm::dmat4 Model = glm::translate(glm::dmat4(1.0), -Position); // Projection = glm::perspective(fovY, aspect, zNear, zFar); // zNear = 0.1, zFar = 1.0995116e12 return Projection * View * Model; } I managed to get rid of z-fighting by using a technique called Logarithmic Depth Buffer described in this article; it works amazingly well, no z-fighting at all, at least not visible.
      Each frame i'm rendering each node by sending the generated matrices this way.
      // set the r_ModelViewProjection uniform // Sneak in the mRadiusMatrix which is a matrix that contains the radius of my planet. Shader::setUniform(0, Camera::getInstance()->getMatrix() * mRadiusMatrix); // set the r_Grid matrix uniform i created earlier. Shader::setUniform(1, r_Grid); grid->render(); My planet's radius is around 6400000.0 units, absurdly large, but that's what i really want to achieve;
      Everything works well, the node's split and merge as you'd expect, however whenever i get close to the surface
      of the planet the rounding errors start to kick in giving me that lovely stairs effect.
      I've read that if i could render each grid relative to the camera i could get better precision on the surface, effectively
      getting rid of those rounding errors.
       
      My question is how can i achieve this relative to camera rendering in my scenario here?
      I know that i have to do most of the work on the CPU with double, and that's exactly what i'm doing.
      I only use double on the CPU side where i also do most of the matrix multiplications.
      As you can see from my vertex shader i only do the usual r_ModelViewProjection * (some vertex coords).
       
      Thank you for your suggestions!
       
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