potential bug openGL

Question

I am attempting to tile an image on the screen using menus. My menu works-tiling in the appropriate way-properly until I move my mouse then the tiling design disappears?

#include <GL/glut.h>    
#include <fstream>      
#include <cstdlib>
#include "TUGL.h"
#include <glui.h>

//Global variables

class GLintPoint
{
  public:
    GLint x;
    GLint y;
};

GLint  numpoints;    
GLintPoint P[10];      


window Win(800,600);
frame Frame;
GLUI *glui;
int mainwindow;

//Function prototypes

void readinpoints();                  
void drawline(GLint from, GLint to);   
void display(void);                   
void init (void);                     
void keyboard(unsigned char key, int x, int y);
void tile1(void);
void tile4(void);
void tile9(void);
void tile16(void);
void myReshape(GLsizei W, GLsizei H);
void define_glui_window();
void choice_selected(int value);
void drawImage(void);
//Main

int main(int argc, char** argv)
{
  glutInit(&argc, argv);
  glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
  glutInitWindowSize (Win.width, Win.height);
  glutInitWindowPosition (100, 100);
  mainwindow = glutCreateWindow ("*star*");

  init();
  define_glui_window();
  glutDisplayFunc(display);
  glutKeyboardFunc(keyboard);  
  glutReshapeFunc(myReshape);
  readinpoints();

  glutMainLoop();
  return 0;
}

//Functions

void init (void)
{
  glClearColor (0.0, 0.0, 0.0, 0.0);    //set background color
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(0.0, 200, 0.0, 249, -1.0, 1.0);

}

void readinpoints()

{
  ifstream infile("polyline.pts");

  numpoints=0;
  infile>>P[numpoints].x>>P[numpoints].y;
  while (!infile.eof())
  {
    numpoints++;
    infile>>P[numpoints].x>>P[numpoints].y;
  }
  numpoints=numpoints-1;
}

void drawline(GLint from, GLint to)

{
  glBegin(GL_LINES);
  {
    glVertex2i(P[from].x, P[from].y);
    glVertex2i(P[to].x, P[to].y);
  }
  glEnd();
}

void drawImage(void);
{
  glClear (GL_COLOR_BUFFER_BIT)
  glColor3f (1.0, 0.0, 1.0);       
  glLineWidth(3);

  drawline(0,1);        
  drawline(1,2);       
  drawline(2,3);        
  drawline(3,4);
  drawline(4,5);
  drawline(5,6);
  drawline(6,7);
  drawline(7,8);
  drawline(8,9);
  drawline(9,0);

  glFlush();

}

void display(void)

{
  glClear (GL_COLOR_BUFFER_BIT);  
  //autoViewPort(Frame, Win); 
  drawImage();            
}

void tile1(void)

{   glClear (GL_COLOR_BUFFER_BIT);
    for(int i=0; i < 1; i++)
      for(int j=0; j < 1; j++)
        {
          //autoViewPort(Frame, Win);
          glViewport(i * 800, j * 600, 800, 600);
          drawImage();
          glFlush();
        }
}
void tile4(void)

{   glClear (GL_COLOR_BUFFER_BIT);
    for(int i=0; i < 2; i++)
      for(int j=0; j < 2; j++)
        {
         // autoViewPort(400, 300);
          glViewport(i * 400, j * 300, 400, 300);
          drawImage();
                  glFlush();
        }
}
void tile9(void)

{
    glClear (GL_COLOR_BUFFER_BIT);
    for(int i=0; i < 3; i++)
      for(int j=0; j < 3; j++)
        {
         // autoViewPort(267, 200);
          glViewport(i * 267, j * 200, 267, 200);
          drawImage();
                  glFlush();
        }
}
void tile16(void)
{
    glClear (GL_COLOR_BUFFER_BIT);
    for(int i=0; i < 4; i++)
      for(int j=0; j < 4; j++)
        {
         // autoViewPort(200, 150);
          glViewport(i * 200, j * 150, 200, 150);
          drawImage();
                  glFlush();
        }
}
void keyboard(unsigned char key, int x, int y)
{
   switch (key) {           
      case 27:     
         exit(0);
         break;
      case 'f': 

    tile4();
    break;
    case 'n': 
    tile9();
    break;
   case 's':
    tile16();
    break;
   case 'o':
    tile1();
    break;
   }
}
void myReshape(GLsizei W, GLsizei H)

{
  Win.set(W,H);
  autoViewPort(Frame, Win);
}

void choice_selected(int value)

{
   switch (value)
   {
     case 1:
       tile1();
       break;
     case 2:
       tile4();
       break;
     case 3:
       tile9();
       break;
     case 4:
       tile16();
       break;
   }
}

void define_glui_window()
{
  glui =  GLUI_Master.create_glui("OPTIONS", 0, 560, 50); 

  GLUI_StaticText *message1 = glui->add_statictext("  BACKGROUND COLOR  ");
  glui->add_button("Tile-1", 1, choice_selected);
  glui->add_button("Tile-4", 2, choice_selected);
  glui->add_button("Tile-9", 3, choice_selected);
  glui->add_button("Tile-16", 4, choice_selected);
  glui->set_main_gfx_window(mainwindow);
  GLUI_Master.sync_live_all();
}

Answer 1

Check for errors with glError() after each OpenGL call. The point which is failing will return an error. Then you can also look up the error code for extra information on what went wrong.