#include <GL/glut.h>
#include <math.h>

// Define a constant for the value of PI
#define GL_PI 3.1415f

// Called to draw scene
void RenderScene(void)
{
  // Clear the window with current clearing color
  glClear(GL_COLOR_BUFFER_BIT);
  
  // ...

  // Flush drawing commands
  glutSwapBuffers();
}

// This function does any needed initialization on the rendering
// context. 
void SetupRC()
{
  // Black background
  glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
}

void SpecialKeys(int key, int x, int y)
{
  /*
  if(key == GLUT_KEY_UP)
    ...
  
  if(key == GLUT_KEY_DOWN)
    ...
  
  if(key == GLUT_KEY_LEFT)
    ...
  
  if(key == GLUT_KEY_RIGHT)
    ...
  */

  // Refresh the Window
  glutPostRedisplay();
}

void ChangeSize(int w, int h)
{
  GLfloat nRange = 25.0f;
  
  // Prevent a divide by zero
  if(h == 0)
    h = 1;
  
  // Set Viewport to window dimensions
  glViewport(0, 0, w, h);
  
  // Reset projection matrix stack
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  
  // Establish clipping volume (left, right, bottom, top, near, far)
  if (w <= h) 
    glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange, nRange);
  else 
    glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange, nRange);
  
  // Reset Model view matrix stack
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

int main(int argc, char* argv[])
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
  glutCreateWindow("alap1");
  glutReshapeFunc(ChangeSize);
  glutSpecialFunc(SpecialKeys);
  glutDisplayFunc(RenderScene);
  SetupRC();
  glutMainLoop();
  
  return 0;
}