/*
 *  darwinView           
 *  Written by Marissa Weichman June-July 2007   
 *  Contact: mweichman@gmail.com        
 *  
 *  See the darwinView Guide for instructions on using this program. 
 *
 *  The program begins running at main(), at the bottom of this file. The function
 *  readjet() reads in the rgb for the color scale, while readnames() fills the array
 *  fns[][][] with the appropriate filenames to read data from. The functions that
 *  do the reading in are readxy(), readxz() and readyz() depending upon which plane
 *  is being viewed (xy, xz and yz, respectively). The functions global() and local()
 *  calculate the global and local maximum and minimum of the data sets. The key()
 *  and specialkey() functions handle keyboard input from the user. Everytime a key
 *  push changes any information, the display() function is called, which redisplays
 *  the plots with the new values. Finally, TimerFunction() is called when the 
 *  autoplay feature is set, and an arrow key is pushed. TimerFunction() calls itself
 *  recursively, and redisplays every 10th of a second as it scrolls through time,
 *  depth levels, etc.       
 */

#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#define WINDOW "image"
#define UP 101
#define DOWN 103
#define RIGHT 102
#define LEFT 100
#define MAX 100 
#define SCALE .06
 
int NX, NY, NZ;

void do_byteswap_f32( float arr[], int nel ), global(), local( int, int, int );
void TimerFunction( int ), stroke( char[], int, int );
void readxy( float[], char[], int), readxz( float[], char[] ), readyz( float[], char[] );
void readnames( char[] ), readjet(), readdepths( char[] );

float data[MAX][MAX*MAX], mxval, mnval, jet[64][3], globalmx=0, globalmn=100;
int glo=0, usr=0, anim=0, endian=1, logscale=0, xz=0, yz=0, nonegs=1, scaledepth=0;
int win[MAX], depths[MAX], ilev=1, howmany, sets, count=0, xmax, ymax, yoffset=0, xoffset=0;
int totaldepth=0, scalecount=0;
char initfns[MAX][MAX], fns[MAX][MAX][MAX];

void menu( int value ){         // called when menu is opened on right click

 switch( value ){
  case 1: usr=glo=0;            // unset glo & usr, sets local max/min
          break;
  case 2: glo=1;                // enables global max/min  
          usr=0;                // unsets usr 
          mxval=globalmx;       // sets max to globalmx
          mnval=globalmn;       // sets min to globalmn
          break;
  case 3: usr=1;                // switch to user-set max/min 
          glo=0;                // unset glo
          printf( "Max = " );  scanf( "%f", &mxval );  // prompt user for new max
          printf( "Min = " );  scanf( "%f", &mnval );  // prompt user for new min
          break;
  case 4: logscale=( logscale+1 )%2;  // toggle log scale
          break;
  case 5: nonegs=( nonegs+1 )%2;      // toggle allowance of negatives 
          break;
  case 6: endian=( endian+1 )%2;      // toggle big/little endian
          break;
 }
 glutPostRedisplay();                 // redisplay with new values
}

void display(){                       // called on glutPostRedisplay
 int i, h, ioff, q; 
 float r, g, b, k, y, j, tmp;
 double num, logmx, logmn;
 char str[MAX]; 


 for( q=0; q<sets; q++ ){             // runs display func for each subwindow
  glutSetWindow( win[q] );            // sets which subwindow to display to
  glClear( GL_COLOR_BUFFER_BIT );     // background to black

  if( xz ) {  xmax=NX;  ymax=NZ;  }   // if in xz view, set y-axis to depth
  else{
   if( yz ){  xmax=NY;  ymax=NZ;  }   // if in yz view, set x-axis to y, y-axis to depth
   else    {  xmax=NX;  ymax=NY;  }   // otherwise, x-axis = x, y-axis = y
  }

  if( glo || usr ){                   // if global or user-set max/min 
   if( xz )                           // if in xz view
    readxz( data[q], fns[q][count] ); // read new xz values w/o calculcating local max/min
   else{
    if( yz )                          // if in yz view
     readyz( data[q], fns[q][count] );// read new yz values w/o calculating local max/min
    else                                         // if in xy view
     readxy( data[q], fns[q][count], ilev );  // read new xy values w/o calculating local max/min
   }
  }
  else                              // if local max/min is set 
   local( q, count, ilev );         // read new array and calculate local max/min

  if( logscale ){                   // if log scale is set
   if( usr ){                       // and values are user-set
    logmx=(double)mxval;            // assume the log has already been taken of max/min
    logmn=(double)mnval;
   }
   else{                            // otherwise
    logmx=log10( mxval );           // take the log of max/min
    logmn=log10( mnval );
   }
  }
 
  if( scaledepth && xz || scaledepth && yz ){ // if scale-depth is set
   ymax=NY;                                   // scale z values to ymax 
   tmp=(float)ymax/totaldepth;                // calculate ratio between z and ymax 
  }

  j=0;                   // counts through y-values
  ioff=0;                // counts through i&j values, because data is 1 dimensional 
  h=0;                   // h counts depth levels if scaledepth is set

  while ( j<ymax ){                   // cycles through y values
   for( i=0; i<xmax; i++ ){           // cycles through x values
    r=g=b=0;                          // set color values to black
    if( data[q][ioff]==0 );           // if data=0, values stay black
    else{
     if( logscale ){                  // if logscale is set
      num=(double)data[q][ioff];
      num=log10( num );               // calculate log of data
      if( num<logmn ) num=0;          // set data less than min to min
      else{
       if( num>logmx ) num=63;        // set data more than max to max
       else
        num=63*( num-logmn )/( logmx-logmn ); // scale all others
      }
     }
     else{                                // if not logscale  
      if( data[q][ioff]<mnval )  num=0;   // set data less than min to min
      else{
       if( data[q][ioff]>mxval )  num=63; // set data more than max to max
       else
        num=63*( data[q][ioff]-mnval )/( mxval-mnval );  // scale all others
      }
     }
     r=jet[(int)num][0];                  // set red value
     g=jet[(int)num][1];                  // set green value
     b=jet[(int)num][2];                  // set blue value  
    }

    glColor3f( r, g, b );                 // put r, g, b into effect
    if( scaledepth && xz || scaledepth && yz )  // if scaledepth is set
     glRectf( i, j, i+1, j+(depths[h]*tmp) );   // draw box appropriate to width of level
    else                                        // otherwise
     glRectf( i, j, i+1, j+1 );                 // draw a square 
    ioff++;                    
   }                                            // leave x loop
   if( scaledepth && xz || scaledepth && yz ){  // if scaledepth is set
    j+=(depths[h]*tmp);                         // scale j by width of current depth level
    h++;                                        // increment h (counts through depth levels)
   }
   else j++;                                    // otherwise, increment j by 1 
  }                                             // leave y loop

  glColor3f( 1, 1, 1 );                         // set color to white
  glRectf( xmax, 0, xmax+1, ymax+1 );           // draw a border right of plot 
  glRectf( 0, ymax, xmax, ymax+1 );             // draw a border on top of plot 

  for( i=0; i<64; i++ ){                        // draw color bar    
   glColor3f( jet[i][0], jet[i][1], jet[i][2]); // sets color
   k=(float)i;                                  // turns i into a float
   y=(float)ymax/64;                            // scales rectangles to fit in ymax
   glRectf( xmax+10, y*k, xmax+20, (k+1)*y );   // draws rectangle 
  } 

  glColor3f( 1, 1, 1 );                         // color to white

  if( logscale )                                            
   sprintf( str, "%.2f", logmx );
  else
   sprintf( str, "%.1e", mxval );               // labels color bar with max val
  stroke( str, xmax+2, ymax-1 );
  
  if( logscale )
   sprintf( str, "%.2f", logmn );
  else
   sprintf( str, "%.1e", mnval );               // labels color bar with min val
  stroke( str, xmax+2, 1 );

  if( xz )                                      // in xz view
   sprintf( str, "N-S slice %d", yoffset+1);    // labels NS slice     
  else{
   if( yz )                                     // in yz view
    sprintf( str, "E-W slice %d", xoffset+1);   // labels EW slice
   else                                         // in xy view
    sprintf( str, "Level %d", ilev );           // labels current level 
  }
  stroke( str, 1, ymax+5 );

  sprintf( str, "Time %d", count+1 );           // labels current time step
  stroke( str, xmax/2, ymax+5 );

  if( glo )                                     // labels how max/min have been set
   sprintf( str, "Global" );                    // if glo is set, display Global
  if( usr ) 
   sprintf( str, "User-set" );                  // if usr is set, display User-set
  if( !usr && !glo ) 
   sprintf( str, "Local" );                     // else display Local 
  stroke( str, xmax+8, ymax+8 );
  
  if( anim ){                                   // tell user if autoplay is on
   sprintf( str, "Autoplay" );
   stroke( str, xmax-35, ymax+8 );
  }

  if( logscale ){
   sprintf( str, "Log Scale" );                 // tell user if log scale is on
   stroke( str, xmax-25, ymax+15); 
  }

  stroke( fns[q][count], 1, ymax+15 );          // labels current file
 
  glutSwapBuffers();                            // double buffering set to animate smoothly
  glFlush(); 
 }
}

void stroke( char str[], int x, int y ){        // called to display text onscreen
 int i;

 glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );  // sets blending mode
 glEnable( GL_BLEND );                                 // enables blending
 glEnable( GL_LINE_SMOOTH );                           // enables smooth lines
 glMatrixMode( GL_MODELVIEW );                         // sets matrix mode 

 glPushMatrix();                                       // push matrix 

 glScalef( SCALE, SCALE, SCALE );                      // scales stroked text 
 glTranslatef( (1/SCALE)*x, (1/SCALE)*y, 0 );          // determines location of text

 for( i=0; i<strlen( str ); i++)                       // stroke each character of str
  glutStrokeCharacter( GLUT_STROKE_ROMAN, str[i] );

 glPopMatrix();                                        // pop matrix
}

void key( unsigned char key, int x, int y ){   // called on key press
 int i, tmp;
 char fn[MAX];
 
 switch(key){
  case 'q':   exit(0);              // close window 
              break;
  case 'r':   count=0;              // reset back to first time    
              ilev=1;               // and first level
              xz=yz=0;              // and xy view 
              break;
  case 'a':   anim=(anim+1)%2;      // toggle autoplay 
              break;
  case 'x':   xz=(xz+1)%2;          // toggle xz/xy view
              yz=0;                 // unset yz view, just in case
              break;
  case 'y':   yz=(yz+1)%2;          // toggle yz/xy view
              xz=0;                 // uset xz view, just in case
              break;
  case 'z':   if( xz || yz ){                   // if xz or yz view is set
               scaledepth=( scaledepth+1 )%2;   // enable depth scaling
               scalecount++;                    
               if( scalecount==1 ){             // read in filename the first time z is pressed
                printf( "Please enter filename containing depth data: " );
                scanf( "%s", fn );
                readdepths( fn );               // read in depth data
               }
              }
              break; 
 } 
 glutPostRedisplay();                           // redisplay with new values
}

void TimerFunction( int value ){    // called when autoplay is set and arrow key is pressed
 int i;

 switch(value){                     // increments in the correct direction
  case DOWN : if( xz && yoffset>0 ) // if down arrow key is pressed  
               yoffset--;           // in xz view, move south
              else{
               if( yz && xoffset<NX-1 )
                xoffset++;          // in yz view, move east
               else 
                if( ilev<NZ && !xz && !yz ) 
                 ilev++;            // in xy view, move down a depth level 
              }
              break;
  case UP   : if( xz && yoffset<NY-1 ) // if up arrow key is ressed
               yoffset++;           // in xz view, move north
              else{
               if( yz && xoffset>0 )
                xoffset--;          // in yz view, move west
               else
                if( ilev>1 && !xz && !yz )    
                 ilev--;            // in xy view, move up a depth level
              }
              break;
  case LEFT : if( count>0 )      
               count--;             // if left arrow is pressed, move back one time step 
              break;
  case RIGHT: if( count<howmany-1 )
               count++;             // if right arrow is pressed, move forward one time step 
              break;
 }
 
 glutPostRedisplay();               // redisplay with new values

 if ( anim )                        // if autoplay is still set
  switch( value ){    
   case DOWN : if( xz && yoffset==0 ) // if furthest south is reached in xz view
                yoffset=NY-1;         // start at the top again
               else{ 
                if( yz && xoffset==NX-1 ) // if furthest east is reached in yz view
                 xoffset=0;               // start in the west again
                else
                 if( ilev==NZ && !xz && !yz )  // if bottom level is reached in xy view
                  ilev=1;                      // start at the surface again
               }
               glutTimerFunc( 100, TimerFunction, value ); // recall timer func
               break;
   case UP   : if( xz && yoffset==NY-1 )  // if furthest north is reached in xz view
                yoffset=0;                // start at the bottom again
               else{
                if( yz && xoffset==0 )    // if furthest west is reached in yz view
                 xoffset=NX-1;            // start in the east again
                else
                 if( ilev==1 && !xz && !yz ) // if top level is reached in xy view
                  ilev=NZ;                   // start at the bottom again 
               }
               glutTimerFunc( 100, TimerFunction, value ); // recall timer func 
               break;
   case LEFT : if( count==0 ) count=howmany-1;             // if first time reached, start at last 
               glutTimerFunc( 100, TimerFunction, value ); // recall timer func 
               break;
   case RIGHT: if( count==howmany-1 ) count=0;             // if last time reached, start at first        
               glutTimerFunc( 100, TimerFunction, value ); // recall timer func 
               break;
  } 
}

void specialkey( int key, int x, int y ){  // called on arrow key press
 int i;

 if( anim )                                // if autoplay is set, call the timer function
  glutTimerFunc( 100, TimerFunction, key); // to scroll automatically

 switch(key){
  case DOWN   :  if( xz && yoffset>0 )     // if you haven't reached the bottom in xz view  
                  yoffset--;               // go down one NS slice
                 else{ 
                  if( yz && xoffset<NY-1 ) // if you haven't reached the edge in yz view
                   xoffset++;              // go east one EW slice
                  else
                   if( ilev<NZ && !xz && !yz ) // if you haven't reached the bottom in xy view
                    ilev++;              // go down one level 
                 } 
                 break;
  case UP     :  if( xz && yoffset<NY-1 )  // if you haven't reached the top in xz view
                  yoffset++;               // go up one NS slice
                 else{
                  if( yz && xoffset>0 )    // if you haven't reached the edge in yz view
                   xoffset--;              // go west one EW slice
                  else
                   if( ilev>1 && !xz && !yz ) // if you haven't reached the top in xy view
                    ilev--;                // go up one level
                 }
                 break;
  case RIGHT  :  if( count<howmany-1 ) // if you haven't reached the last time step
                  count++;             // go forward one time step 
                 break;
  case LEFT   :  if( count>0 )         // if you haven't reached the first time step
                  count--;             // go back one time step
                 break;
 }
 glutPostRedisplay();                  // redisplay with new values      
}

void global(){                         // calculates the max/min for the total data set
 FILE* fp;
 int h, i, j;
 for( h=0; h<sets; h++)                // cycles through each window 
  for( i=0; i<howmany; i++ )           // cycles through each time 
   for( j=0; j<NZ; j++ ){              // cycles through each depth level
    local( h, i, j );                  // calculates local max/min for specific data set 
    if( mxval > globalmx ) globalmx = mxval;   // sets highest value to globalmx
    if( mnval < globalmn ) globalmn = mnval;   // sets lowest value to globalmn
   }
}

void local( int i, int time, int lev ){        // calculates local max/min
 int j;
 
 mxval=0;
 mnval=100;
 if( xz )
  readxz( data[i], fns[i][time]);              // if xz view, reads new array of xz vals
 else{
  if( yz )
   readyz( data[i], fns[i][time]);             // if yz view, reads new array of yz vals 
  else
   readxy( data[i], fns[i][time], lev );    // if xy view, reads new array of xy vals 
 }
 for( j=0; j<xmax*ymax; j++ ){                 // cycles through all values in the array
  if( data[i][j] > mxval ) 
   mxval=data[i][j];                           // set largest val to mxval 
  if( data[i][j] < mnval && data[i][j]!=0 ) 
   mnval=data[i][j];                           // set smallest nonzero val to mnval 
 }
}

void readnames( char filename[] ){             // reads in list of filenames 
 FILE* fp;
 int i=0, j=0;
 
 fp=fopen( filename, "r" );                    // opens list of filenames
 while( !feof(fp) ){                           // reads until the end of the file 
  fscanf( fp, "%s", initfns[i] );              // places filename into an array of strings 
  i++;                                         // counts how many filenames there are  
 } 
 fclose( fp );                                 // close file
 sets=i-1;                                     // saves number of initial filenames 
 
 for(i=0; i<sets; i++){                        // goes through each filename just read in
  fp=fopen( initfns[i], "r" );                 // opens each filename  
  j=0;
  while( !feof(fp) ){                          // reads in filenames from each filename 
   fscanf( fp, "%s", fns[i][j]);               
   j++;
  }
  fclose(fp);                                  // close file
 }
 howmany=j-1;                                  // saves number of time steps  
}

void readdepths( char filename[] ){            // called when the scale depth feature is enabled
 int i;
 FILE* fp;

 fp=fopen( filename, "r" );                    // open depth data file

 for( i=NZ-1; i>=0; i-- ){                     // read in data backwards, starting at the lowest depth
  fscanf( fp, "%d ", &depths[i] );
  totaldepth+=depths[i];                       // calculate total depth
 } 

 fclose( fp );                                 // close file
}

void readjet(){               // read in color scale values
 FILE* fp;
 int i, j; 
  
 fp=fopen( "jet.dat", "r" );  // open file containing values
 for( i=0; i<64; i++ )        // read in 64 sets of rgb values
  for( j=0; j<3; j++ )
   fscanf( fp, "%f", &jet[i][j] );
 fclose( fp );                // close file
}

void readxz( float arr[], char filename[] ){  // reads in xz values
 int i, j;
 float tmp[MAX][MAX];
 FILE* fp;
 
 fp=fopen( filename, "rb" );                         // open data file
 for( i=0; i<NZ; i++ ){                              // run through each depth level
  fseek( fp, (NX*yoffset*4)+(i*NX*NY*4), SEEK_SET ); // seek to correct place in the file 
  fread( &arr[NX*i], sizeof( arr[0] ), NX, fp );     // reads in one row of x-values 
 }
 fclose( fp );                                       // close file

 for( i=0; i<NZ; i++ ) // the array should start at the ocean floor and move upwards
  for( j=0; j<NX; j++) // so it has been read in backwards
   tmp[i][j]=arr[i*NX+j]; // put each row of x-values into a 2d array 

 for( i=0; i<NZ; i++ )  
  for( j=0; j<NX; j++)
   arr[i*NX+j]=tmp[NZ-i-1][j];  // flip the order of the rows, and store in the data array

 if( nonegs ) 
  for( i=0; i<NX*NZ; i++ )                    
   if( arr[i] < 0 ) 
    arr[i] = pow(10, -20);      // sets negative values to 10^-20 

 if( endian )
  do_byteswap_f32( arr, NX*NZ );            // switches endian 
}

void readyz( float arr[], char filename[] ){  // reads in yz values
 int i, j;
 float tmp[MAX][MAX];
 FILE* fp;  
 
 fp=fopen( filename, "rb" );                         // open data file
 for( i=0; i<NY*NZ; i++ ){                           // run through each line in the file
  fseek( fp, (xoffset*4)+(i*NX*4), SEEK_SET );       // seek to the correct place in the file  
  fread( &arr[i], sizeof( arr[0] ), 1, fp );         // reads in one y-value at the correct x
 }
 fclose(fp);                                         // close file

 for( i=0; i<NZ; i++ ) // the array should start at the ocean floor and move upwards
  for( j=0; j<NY; j++) // so it has been read in backwards
   tmp[i][j]=arr[i*NY+j]; // put each row of x-values into a 2d array

 for( i=0; i<NZ; i++ )
  for( j=0; j<NY; j++)
   arr[i*NY+j]=tmp[NZ-i-1][j];  // flip the order of the rows, and store in the data array

 if( nonegs ) 
  for( i=0; i<NY*NZ; i++ )                    
   if( arr[i] < 0 ) 
    arr[i] = pow(10, -20);   // sets negative values to 10^-20 

 if( endian )
  do_byteswap_f32( arr, NY*NZ );            // switches endian 

}

void readxy( float arr[], char filename[], int il ){   // reads in xy values 
 FILE* fp;
 int i;
 
 fp=fopen( filename, "rb" );                 // opens the file containing data
 fseek( fp, (il-1)*NX*NY*4, SEEK_SET );      // seeks to the correct place
 fread( arr, sizeof( arr[0] ), NX*NY, fp );  // reads in data to fill one level 
 fclose( fp );                               // close file

 if( nonegs ) 
  for( i=0; i<NX*NY; i++ )                    
   if( arr[i] < 0 ) 
    arr[i] = pow(10, -20);   // sets negative values to 10^-20 

 if( endian )
  do_byteswap_f32( arr, NX*NY );            // switches endian 
}

void do_byteswap_f32( float arr[], int nel ){ // switches endian

 int i;
 char src[4], trg[4];

 for( i=0; i<nel; i++ ){
  memcpy( src, &(arr[i]), 4 );
  trg[0]=src[3];
  trg[1]=src[2];
  trg[2]=src[1];
  trg[3]=src[0];
  memcpy( &(arr[i]), trg, 4 );
 }
}

void black( ){                   // display func for extra windows
 glClear( GL_COLOR_BUFFER_BIT );
 glutSwapBuffers();
 glFlush();
}


int main( int argc, char *argv[] ){
 int i, setsx, setsy, tmpx, tmpy, winx, winy, parent;
 char str[MAX], filename[MAX];
 FILE* fp;

 printf("Hello 1\n");
 if( strcmp(argv[1], "binary") == 0 )       // if data files are binary open binconfig 
  fp=fopen( ".darwinview/binconfig", "r" );
 else
  if( strcmp(argv[1],"netcdf") == 0 )       // if data files are netcdf open ncconfig
   fp=fopen( ".darwinview/ncconfig", "r" );
 printf("Hello 2\n");

 fscanf( fp, "%dx%d ", &winx, &winy );      // read in screen resolution
 printf("Hello 3\n");
 winy-=60;  winx-=20;                       // adjust resolution so edges won't get cut off             
 fscanf( fp, "%d %d %d ", &NX, &NY, &NZ );  // read in dimensions of data
 fscanf( fp, "%dx%d ", &setsx, &setsy );    // read in dimensions of subwindows
 fscanf( fp, "%s", filename );              // read in name of file containing data filenames 

 fclose( fp );                              // close file

 xmax=NX; ymax=NY;                          // default to xy 
 printf("Hello 4\n");

 readjet();                                 // stores color values
 printf("Hello 5\n");
 readnames( filename );                     // gets list of filenames to read from
 printf("Hello 6\n");
 global();                                  // calculates max and min for all data
 printf("Hello 7\n");

 glutInit( &argc, argv );                 
 glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE );   // set rgb mode and double buffering
 glutInitWindowSize( winx, winy );                // parent window will cover screen
 glutInitWindowPosition( 10, 10 );                // set location of parent window
 parent=glutCreateWindow( WINDOW );               // create parent window

 glClearColor( 0, 0, 0, 0 );                      // set clear color to black
 gluOrtho2D( 0, winx , winy, 0 );                 // set (0,0) as top left corner 
 glutDisplayFunc( display );                      // declares display func
 glutKeyboardFunc( key );                         // called on key press
 glutSpecialFunc( specialkey );                   // called on special key press (arrow keys)
 

 for( i=0; i<setsx*setsy; i++ ){                  // for each subwindow 
  tmpx = (i%setsx)*(winx/setsx);                  // x coordinate of top left corner of subwindow
  tmpy = (i/setsx)*(winy/setsy);                  // y coordinate of top left corner of subwindow 

  win[i]=glutCreateSubWindow( parent, tmpx, tmpy, winx/setsx, winy/setsy ); // creates subwindow
  gluOrtho2D( 0, NX+35, 0, NY+25 );               // sets how data is mapped to subwindow
  glutKeyboardFunc( key );                        // called on key press
  glutSpecialFunc( specialkey );                  // called on special key press (arrow keys)
  if( i >= sets )                                 // if there are more subwindows than data sets 
   glutDisplayFunc( black );                      // color those windows black 
  else                                            // otherwise 
   glutDisplayFunc( display );                    // sets display func for subwindow
  

  glutCreateMenu( menu );                                // adds a menu
   glutAddMenuEntry( "Local Color Scale", 1 );           // adds a menu entry 
   glutAddMenuEntry( "Global Color Scale", 2 );          // adds a menu entry 
   glutAddMenuEntry( "User-Set Color Scale", 3 );        // adds a menu entry 
   glutAddMenuEntry( "Log Scale (on/off)", 4 );          // adds a menu entry 
   glutAddMenuEntry( "Allow Negatives (on/off)", 5 );    // adds a menu entry
   glutAddMenuEntry( "Switch Endian (big/little) ", 6);  // adds a menu entry
  glutAttachMenu( GLUT_RIGHT_BUTTON );                   // menu called on right click
 }

 glutMainLoop();                                  // begin processing events
 return 0;
}