OpenGL和GLFW：不绘制多边形

Question

I am able to create a window and clear it to the desired color. But not able to draw a square in the lower left hand corner.

#include <iostream>

#define GLEW_STATIC

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

const GLint WIDTH = 720;
const GLint HEIGHT = 480;

int main()
{
    glfwInit();

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); // Attempts to set to opengl 3.3
    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, "Learn OpenGL", nullptr, nullptr);

    int screenWidth, screenHeight;

    glfwGetFramebufferSize(window, &screenWidth, &screenHeight);

    if (nullptr == window)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();

        return EXIT_FAILURE;
    }

    glfwMakeContextCurrent(window);

    glewExperimental = GL_TRUE;

    if (GLEW_OK != glewInit())
    {
        std::cout << "Failed to initialise GLEW" << std::endl;

        return EXIT_FAILURE;
    }

    glViewport(0, 0, screenWidth, screenHeight);

    while (!glfwWindowShouldClose(window))
    {
        glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glColor3f(0.0f, 0.0f, 1.0f);
        glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);

        glBegin(GL_POLYGON);
            glVertex3f(0.0, 0.0, 0.0);
            glVertex3f(0.5, 0.0, 0.0);
            glVertex3f(0.5, 0.5, 0.0);
            glVertex3f(0.0, 0.5, 0.0);

        glEnd();
        glFlush();

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwTerminate();

    return EXIT_SUCCESS;
}

Answer 1

Deprecated fixed-function functionality ( glBegin() et al & the matrix stacks) doesn't work in a Core context ( GLFW_OPENGL_CORE_PROFILE ).

Switch to a Compatibility context:

#include <iostream>

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

const GLint WIDTH = 720;
const GLint HEIGHT = 480;

int main()
{
    glfwInit();

    glfwWindowHint(GLFW_RESIZABLE, GL_TRUE);

    GLFWwindow *window = glfwCreateWindow(WIDTH, HEIGHT, "Learn OpenGL", nullptr, nullptr);

    int screenWidth, screenHeight;

    glfwGetFramebufferSize(window, &screenWidth, &screenHeight);

    if (nullptr == window)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();

        return EXIT_FAILURE;
    }

    glfwMakeContextCurrent(window);

    glewExperimental = GL_TRUE;

    if (GLEW_OK != glewInit())
    {
        std::cout << "Failed to initialise GLEW" << std::endl;

        return EXIT_FAILURE;
    }

    glViewport(0, 0, screenWidth, screenHeight);

    while (!glfwWindowShouldClose(window))
    {
        glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glMatrixMode( GL_PROJECTION );
        glLoadIdentity();
        glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);

        glMatrixMode( GL_MODELVIEW );
        glLoadIdentity();

        glColor3f(0.0f, 0.0f, 1.0f);
        glBegin(GL_POLYGON);
            glVertex3f(0.0, 0.0, 0.0);
            glVertex3f(0.5, 0.0, 0.0);
            glVertex3f(0.5, 0.5, 0.0);
            glVertex3f(0.0, 0.5, 0.0);
        glEnd();

        glfwSwapBuffers(window);

        glfwPollEvents();
    }

    glfwTerminate();

    return EXIT_SUCCESS;
}

Or supply some shaders & use a VAO & VBO to upload your geometry.