//  This program shows how to open a single window and plot bitmapped text
//  on the screen in Times Roman font. 
#include <string.h>
#include <stdio.h>
#include <stdarg.h>
#include <GL/glut.h>

#define initial_width 400             // Initial Window Width = 400 pixels
#define initial_height 400            // Initial Window Height = 400 pixels

int main_window, sub_window;          // Outer Window and Inner Window ID numbers 
// Draw text on the screen using pre-defined Bitmap character fonts 
// Passed arguments include location in 3-space, pointer to string, pointer to font
void bitmap_output(int x, int y, int z, char *string, void *font)
{  int len, i;
   glRasterPos3f(x, y, 0);            // Locate Raster Position in 3-space
   len = (int) strlen(string);        // Find length of string
   for (i = 0; i < len; i++) {        // Loop through plotting all characters in font style
       glutBitmapCharacter(font, string[i]);
      }
}

// Draw a graph of a simple line.

DrawGraph()
{ float x;
  glBegin(GL_POINTS);                         // Start drawing points
    glColor3f(0.0,0.0,0.0);                   // Set drawing color to black
    for (x=-0.9; x<0.9; x+=0.01)              // Step through x values
     {glVertex3f(x,x,0.0);                    // Put a point at (x,x)
     }
  glEnd();
} 

// Draw a set of labeled axes

DrawAxes()
{  glBegin(GL_LINES);                         // Start Drawing Lines
    glColor3f(1.0, 1.0, 0.0);                 // Set Drawing Color
    glVertex3f(-0.9,0.0, 0.0);                // Starting Point for x-axis
    glVertex3f(0.9, 0.0, 0.0);                // Ending Point
    glVertex3f(0.0, -0.9,0.0);                // Staring Point for y-axiz
    glVertex3f(0.0, 0.9, 0.0);                // Ending Point
  glEnd();
 
// Now label the axes

  glPushMatrix();                             // New frame of reference
    glTranslatef(0.05, 0.85, 0);              // Move to new location
    bitmap_output(0,0,0, "y", GLUT_BITMAP_TIMES_ROMAN_24);
  glPopMatrix();                              // Return to old reference

  glPushMatrix();                             // New frame of reference
    glTranslatef(0.8, -0.1, 0);               // Move to new location
    bitmap_output(0,0,0, "x", GLUT_BITMAP_TIMES_ROMAN_24);
  glPopMatrix();                              // Return to old reference
 
}

//Draw some titles on the screen in available Times Roman fonts

void DrawTitles()
{ glColor3f(0.0, 0.0, 0.0);                   // Set color to Black
  glPushMatrix();                             // New frame of reference
  glTranslatef(-0.9, 0.8, 0);                 // Move to new location
  bitmap_output(0,0,0, "Example #1", GLUT_BITMAP_TIMES_ROMAN_24);
  glPopMatrix();                              // Return to old reference

  glPushMatrix();                             // New frame of reference
  glTranslatef(-0.5, -0.95, 0);               // Move to new location
  bitmap_output(0,0,0, "The above graph is for the linear equation   y = x", 
                GLUT_BITMAP_TIMES_ROMAN_10);
  glPopMatrix();                              // Reurn to old reference
} 
  
// Display window 

void display1(void)
{ 
  glClear(GL_COLOR_BUFFER_BIT);
  DrawAxes();                                 
  DrawGraph();
  DrawTitles();
  glFlush();                                  // Force all drawing
}
void init(void)
{ /* select clearing (background) color   */
   glClearColor(1.0, 0.0, 0.0, 0.0);

/* initialize viewing values */
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
}
                               

int main(int argc, char **argv)
{
  glutInit(&argc, argv);                      // Initialize with any passed arguments to main
  glutInitDisplayMode(GLUT_RGB);              // Initialize RGB mode in OpenGL
  glutInitWindowSize(initial_width, initial_height);  // Initialize window
  main_window = glutCreateWindow("My First Window ");  // Create main window with title
  init();				      // My initialization
  glutDisplayFunc(display1);                  // Pass pointer to inner window display
  glClearColor(1.0, 0.0, 0.0, 1.0);           // Set drawing color to red
  glutMainLoop();                             // Enter main loop - wait for interrupts
  return 0;             /* ANSI C requires main to return int. */
}