//
// This code was created by Jeff Molofee '99
// (ported to Linux/GLUT by Richard Campbell '99)
//
// If you've found this code useful, please let me know.
//
// Visit me at www.demonews.com/hosted/nehe
// (email Richard Campbell at [email protected])
//
#include <GL/glut.h>    // Header File For The GLUT Library
#include <GL/gl.h>   // Header File For The OpenGL32 Library
#include <GL/glu.h>  // Header File For The GLu32 Library
#include <unistd.h>     // Header File For sleeping.

/* ASCII code for the escape key. */
#define ESCAPE 27

/* The number of our GLUT window */
int window;

/* rotation angle for the triangle. */
float rtri = 0.0f;

/* rotation angle for the quadrilateral. */
float rquad = 0.0f;

/* A general OpenGL initialization function.
   Sets all of the initial parameters. */
void InitGL(int Width, int Height)       // We call this right after our OpenGL
                                         // window is created.
{
  glClearColor(0.0f, 0.0f, 0.0f, 0.0f);  // This Will Clear The Background
                                         // Color To Black
  glClearDepth(1.0);                     // Enables Clearing Of The Depth Buffer
  glDepthFunc(GL_LESS);                  // The Type Of Depth Test To Do
  glEnable(GL_DEPTH_TEST);               // Enables Depth Testing
  glShadeModel(GL_SMOOTH);               // Enables Smooth Color Shading

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();                      // Reset The Projection Matrix

  gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f);
                                    // Calculate The Aspect Ratio Of The Window

  glMatrixMode(GL_MODELVIEW);
}

/* The function called when our window is resized
   (which shouldn't happen, because we're fullscreen) */
void ReSizeGLScene(int Width, int Height)
{
  if (Height==0)         // Prevent A Divide By Zero If The Window Is Too Small
    Height=1;

  glViewport(0, 0, Width, Height);  // Reset The Current Viewport And
                                    // Perspective Transformation
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();

  gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f);
  glMatrixMode(GL_MODELVIEW);
}

/* The main drawing function. */
void DrawGLScene()
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);   // Clear The Screen And
                                                        // The Depth Buffer
  glLoadIdentity();                 // Reset The View

  glTranslatef(-1.5f,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0

  glRotatef(rtri,0.0f,1.0f,0.0f);   // Rotate The Triangle On The Y axis
  // draw a triangle (in smooth coloring mode)
  glBegin(GL_POLYGON);              // start drawing a polygon
  glColor3f(1.0f,0.0f,0.0f);        // Set The Color To Red
  glVertex3f( 0.0f, 1.0f, 0.0f);    // Top
  glColor3f(0.0f,1.0f,0.0f);        // Set The Color To Green
  glVertex3f( 1.0f,-1.0f, 0.0f);    // Bottom Right
  glColor3f(0.0f,0.0f,1.0f);        // Set The Color To Blue
  glVertex3f(-1.0f,-1.0f, 0.0f);    // Bottom Left
  glEnd();                          // we're done with the polygon (smooth
                                    // color interpolation)
  glLoadIdentity();                 // make sure we're no longer rotated.
  glTranslatef(1.5f,0.0f,-6.0f);    // Move Right 3 Units, and back into the
                                    // screen 6.0
  glRotatef(rquad,1.0f,0.0f,0.0f);  // Rotate The Quad On The X axis
  // draw a square (quadrilateral)
  glColor3f(0.5f,0.5f,1.0f);        // set color to a blue shade.
  glBegin(GL_QUADS);                // start drawing a polygon (4 sided)
  glVertex3f(-1.0f, 1.0f, 0.0f);    // Top Left
  glVertex3f( 1.0f, 1.0f, 0.0f);    // Top Right
  glVertex3f( 1.0f,-1.0f, 0.0f);    // Bottom Right
  glVertex3f(-1.0f,-1.0f, 0.0f);    // Bottom Left
  glEnd();                          // done with the polygon

  rtri+=15.0f;               // Increase The Rotation Variable For The Triangle
  rquad-=15.0f;              // Decrease The Rotation Variable For The Quad

  // swap the buffers to display, since double buffering is used.
  glutSwapBuffers();
}

/* The function called whenever a key is pressed. */
void keyPressed(unsigned char key, int x, int y)
{
    /* sleep to avoid thrashing this procedure */
    usleep(100);

    /* If escape is pressed, kill everything. */
    if (key == ESCAPE)
    {
        /* shut down our window */
        glutDestroyWindow(window);

        /* exit the program...normal termination. */
        exit(0);
    }
}

int main(int argc, char **argv)
{
  /* Initialize GLUT state - glut will take any command line arguments
     that pertain to it or X Windows - look at its documentation at
     http://reality.sgi.com/mjk/spec3/spec3.html */
  glutInit(&argc, argv);

  /* Select type of Display mode:
     Double buffer
     RGBA color
     Alpha components supported
     Depth buffer */
  glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH);

  /* get a 640 x 480 window */
  glutInitWindowSize(640, 480);

  /* the window starts at the upper left corner of the screen */
  glutInitWindowPosition(0, 0);

  /* Open a window */
  window = glutCreateWindow("Jeff Molofee's GL Code Tutorial ... NeHe '99");

  /* Register the function to do all our OpenGL drawing. */
  glutDisplayFunc(&DrawGLScene);

  /* Go fullscreen.  This is as soon as possible. */
  glutFullScreen();

  /* Even if there are no events, redraw our gl scene. */
  glutIdleFunc(&DrawGLScene);

  /* Register the function called when our window is resized. */
  glutReshapeFunc(&ReSizeGLScene);

  /* Register the function called when the keyboard is pressed. */
  glutKeyboardFunc(&keyPressed);

  /* Initialize our window. */
  InitGL(640, 480);

  /* Start Event Processing Engine */
  glutMainLoop();

  return 1;
}