https://stackoverflow.com/a/50457770

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

void refresh( GLFWwindow* window )
{
    static double prv = glfwGetTime();
    const double cur = glfwGetTime();
    const double dt = ( cur - prv );
    prv = cur;

    int w, h;
    glfwGetFramebufferSize( window, &w, &h );
    glViewport( 0, 0, w, h );

    glClearColor( 0, 0, 0, 1 );
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    const float degPerSec = 45.0f;
    static float angle = 0.0f;
    angle += degPerSec * dt;

    glRotatef( angle, 0, 0, 1 );

    glScalef( 0.5, 0.5, 0.5 );
    glBegin( GL_TRIANGLES );
    glColor3ub( 255, 0, 0 );
    glVertex2f(  0,  1 );
    glColor3ub( 0, 255, 0 );
    glVertex2f( -1, -1 );
    glColor3ub( 0, 0, 255 );
    glVertex2f(  1, -1 );
    glEnd();

    glfwSwapBuffers( window );
}

void resize( GLFWwindow* window, int width, int height )
{
    refresh( window );
}

int main( int argc, char** argv )
{
    glfwInit();
    std::cout << "GLFW version: " << glfwGetVersionString() << std::endl;
    GLFWwindow* window = glfwCreateWindow( 640, 480, "Drag Test", NULL, NULL );
    glfwSetTime( 0.0 );
    glfwMakeContextCurrent( window );
    glewInit();
    glGetError();

    glfwSetWindowSizeCallback( window, resize );
    glfwSetWindowRefreshCallback( window, refresh );
    while( !glfwWindowShouldClose( window ) )
    {
        glfwPollEvents();
        refresh( window );
    }

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