OpenGL tutorial 4

//http://www.youtube.com/user/thecplusplusguy
//Thanks for the typed in code to Tapit85
#include <SDL/SDL.h>
#include <GL/gl.h>
#include <GL/glu.h>
//-lGL -lGLU
//opengl32
//glu32

float angle = 0.0;
const int triangle = 1;

void init()
{
    glClearColor(1.0,0.0,0.0,1.0);  //background color and alpha
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45,640.0/480.0,1.0,500.0);
//  glOrtho(...?);
    glMatrixMode(GL_MODELVIEW);
//  glShadeModel(GL_FLAT);      // no color interpolation
//  glShadeModel(GL_SMOOTH);    // color interpolation (default)
//  glColor3f(0.0,1.0,0.0);
    glNewList(triangle, GL_COMPILE);
        glBegin(GL_TRIANGLES);
            glColor3f(1.0,0.0,0.0);
            glVertex3f(0.0,2.0,0.0);
            glColor3f(0.0,1.0,0.0);
            glVertex3f(-2.0,-2.0,0.0);
            glColor3f(0.0,0.0,1.0);
            glVertex3f(2.0,-2.0,0.0);
        glEnd();
    glEndList();
}

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    glTranslatef(0.0,0.0,-5.0);
    glRotatef(angle,0.0,1.0,0.0);   // angle, x-axis, y-axis, z-axis
    glCallList(triangle);
}

int main(int argc, char** argv)
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface *screen;
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_OPENGL);
//  screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_FULLSCREEN);
    bool running = true;
    const int FPS = 30;
    Uint32 start;
    SDL_Event event;
    init();
    while(running) {
        start = SDL_GetTicks();
        while(SDL_PollEvent(&event)) {
            switch(event.type) {
                case SDL_QUIT:
                    running = false;
                    break;
            }
        }

        display();
        SDL_GL_SwapBuffers();
        angle += 0.5;
        if(1000/FPS > SDL_GetTicks()-start)
            SDL_Delay(1000/FPS-(SDL_GetTicks()-start));
    }
    SDL_Quit();
    return 0;
}