OpenGL and GLFW: Not drawing polygon - c++

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.