CODEWITHSUNDEEP
c++openglglfw
ronalama
ronalama

Reputation: 39

Why is OpenGL GLFW Rendering shapes not working?

I am trying to get started with openGL and GLFW in c++. My expectation is that the following code will simply render a square on the screen, but I just get a black screen.

The actual setup is working though, because if I add glClearColor(0.1f, 0.4f, 0.8f, 1.0f);, I do indeed get a blue screen. But what is wrong with my use of GL_QUADS?

#include <iostream>

// GLEW
#define GLEW_STATIC
#include <GL/glew.h>

//GLFW
#include <GLFW/glfw3.h>

const GLint WIDTH = 800, HEIGHT = 600;

int main() {
    glfwInit();
    glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint( GLFW_RESIZABLE, GL_TRUE);
    
    GLFWwindow *window = glfwCreateWindow(WIDTH, HEIGHT, "Isosurface Stuffing", nullptr, nullptr);
    
    int screenWidth, screenHeight;
    glfwGetFramebufferSize(window, &screenWidth, &screenHeight);
    
    if (window == nullptr) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        
        return -1;
    }
    
    glfwMakeContextCurrent(window);
    glewExperimental = GL_TRUE;
    
    if (GLEW_OK != glewInit()) {
        std::cout << "Failed to create GLEW" << std::endl;
        
        return -1;
    }
    
    
    while (!glfwWindowShouldClose(window)) {
        
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glLoadIdentity();

        glViewport(0, 0, screenWidth, screenHeight);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(0.0f, screenWidth, 0.0f, screenHeight, 0.0f, 1.0f);
        glMatrixMode (GL_MODELVIEW);
        glLoadIdentity();
        
        
        glfwPollEvents();

        glColor3f(0.5f, 0.5f, 0.5f);
        glBegin(GL_QUADS);

        glVertex2f(100, 100);
        glVertex2f(200, 100);
        glVertex2f(200, 200);
        glVertex2f(100, 200);
        glEnd();

        glfwSwapBuffers(window);
    }
    
    glfwTerminate();
    return 0;
}

Upvotes: 3

Views: 565

Answers (1)

Rabbid76
Rabbid76

Reputation: 211277

You cannot use the legacy fixed-function pipeline instructions (glBegin, glEnd, glVertex2f, glMatrixMode, glLoadIdentity, glOrtho) in a Core profile OpenGL context (GLFW_OPENGL_CORE_PROFILE). You have to use Compatibility profile OpenGL Context:

glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);

If your system does not allow you to create a compatibility profile context (e.g. Mac), you must use either an OpenGL 2.0 context or a modern OpenGL with Shaders and Vertex Array Objects. A nice tutorial for that is LearnOpenGL

Upvotes: 4

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