I'm just starting to play with opengl so i used my friend's program written in C and "translated" it to perl (i read here that it works)... And for some reason it doesn't work... it makes a window, but no lines are drawn (the program is supposed to draw 2 lines for every 2 mouseclicks (start and end point for one line))... where could be the problem? P.S. friend said his program (in C) works when he runs it here is the code...

#!/usr/bin/perl -w

use strict;
use OpenGL qw/ :all /;
#use Math::Trig;

my (@Lx, @Ly, $Ix);

#my $window; 
my ($sub_width,$sub_height) = (800,600);

#*************************************************
#    Glavni program.
#*************************************************

    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize($sub_width,$sub_height);
    glutInitWindowPosition(200,400);
    glutInit();
    
    #$window = glutCreateWindow("Glut OpenGL Linija");
    glutCreateWindow("Glut OpenGL Linija");
    glutReshapeFunc(\&myReshape);
    
    
    glutDisplayFunc(\&myDisplay);
    
    
    glutMouseFunc(\&myMouse);
    glutKeyboardFunc(\&myKeyboard);
    
    
    print "Lijevom tipkom misa zadaj tocke - algoritam Bresenham-a\n";
    print "Tipke r, g, b, k mijenjaju boju.\n";
    
    glutMainLoop();


#*******************************************
#    Osvjezavanje prikaza. (nakon preklapanja prozora) 
#*******************************************

sub myDisplay{
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glFlush();
}

#*******************************************
#    Promjena velicine prozora.
#*******************************************

sub myReshape{
    
    my ($width, $height) = @_;
    $sub_width = $width;
    $sub_height = $height;
    
    $Ix = 0;
    glViewport(0, 0, $sub_width, $sub_height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, $sub_width, 0, $sub_height);
    glClearColor( 1.0, 1.0, 1.0, 0.0 );
    glClear( GL_COLOR_BUFFER_BIT );
    glPointSize(1.0);
    glColor3f(0.0, 0.0, 0.0);
}

#**********************************************
#    Crtaj moju liniju.
#**********************************************

sub crtajLinijuKut0{
    
    my ($pocetniX, $pocetniY, $zavrsniX, $zavrsniY) = @_;
    print "Usao u KUT 0 !\n";
    my $x = $pocetniX<$zavrsniX ? $pocetniX : $zavrsniX;
    my $y = $pocetniY;
    
    my $deltaX = $zavrsniX - $pocetniX;
    
    glBegin(GL_POINTS);
    for (0..abs($deltaX)){
        glVertex2i($x, $y);        
        $x++;
    }
    glEnd();
}
sub crtajLinijuKut90{
    
    my ($pocetniX, $pocetniY, $zavrsniX, $zavrsniY) = @_;
    print "Usao u KUT 90 !\n";
    my $x = $pocetniX;                                  
    my $y = $pocetniY<$zavrsniY ? $pocetniY : $zavrsniY;
    
    my $deltaY = $zavrsniY - $pocetniY;
    
    glBegin(GL_POINTS);
    for (0..abs($deltaY)){
        glVertex2i($x, $y);        
        $y++;
    }
    glEnd();
}

sub crtajLinijuKutDo45{
    
    my ($pocetniX, $pocetniY, $zavrsniX, $zavrsniY) = @_;
    print "Usao u KUT DO 45 !\n";
    my $x = $pocetniX;                                  
    my $y = $pocetniY;
    my $incX = 1;
    my $incY = 1;
    my $deltaX = $zavrsniX - $pocetniX;
    my $deltaY = $zavrsniY - $pocetniY;
    my $nagibPravca = abs($deltaY/$deltaX);
    
    if (($deltaX < 0)){
        $incX = -1;
    }
    
    if ($deltaY < 0){
        $incY = -1;
        $nagibPravca = -$nagibPravca;
    }
    
    my $pogreska = 0;
    
    glBegin(GL_POINTS);
    for (0..abs($deltaX)){
        glVertex2i($x, $y);
        if ( abs($pogreska + $nagibPravca) < 0.5 ) {
            $pogreska += $nagibPravca;
        }else{
            $y += $incY;
            $pogreska += $nagibPravca - $incY;
        }
        $x += $incX;
    }
    glEnd();
}

sub crtajLinijuKutDo90{
    
    my ($pocetniX, $pocetniY, $zavrsniX, $zavrsniY) = @_;
    print "Usao u KUT DO 90 !\n";
    my $x = $pocetniX;                                  
    my $y = $pocetniY;
    my $incX = 1;
    my $incY = 1;
    my $deltaY = $zavrsniX - $pocetniX;
    my $deltaX = $zavrsniY - $pocetniY;
    my $nagibPravca = $deltaY/$deltaX;
    
    if ($deltaX < 0){
        $incY = -1;
        $nagibPravca = -$nagibPravca;
    }
    
    if ($deltaY < 0){
        $incX = -1;
    }
    
    my $pogreska = 0;
    
    glBegin(GL_POINTS);
    for (0..abs($deltaX)){
        glVertex2i($x, $y);
        if (abs($pogreska + $nagibPravca) < 0.5){
            $pogreska += $nagibPravca;
        }else{
            $x += $incX;
            $pogreska += $nagibPravca - $incX;
        }
        $y += $incY;
    }
    glEnd();
}



sub myLine{    
    
    my ($pocetniX, $pocetniY, $zavrsniX, $zavrsniY) = @_;
    my $deltaX = abs($zavrsniX - $pocetniX);
    my $deltaY = abs($zavrsniY - $pocetniY);
    
    my $nagibPravca=abs($deltaY/$deltaX);
    
    #*****************************
    #    NACRTAJ OBICNU LINIJU
    #*****************************
    glColor3f(1., 0, 0);
    glBegin(GL_LINES);
    {
        glVertex2i($pocetniX, $pocetniY + 25);
        glVertex2i($zavrsniX, $zavrsniY + 25);
    }
    glEnd();
    glColor3f(0, 0, 0);
    
    
    #*****************************
    #    BRESENHAMOV POSTUPAK
    #****************************
    
    if ($deltaX == 0){
        &crtajLinijuKut0($pocetniX, $pocetniY, $zavrsniX, $zavrsniY);
    }elsif ($deltaY == 0){
        &crtajLinijuKut90($pocetniX, $pocetniY, $zavrsniX, $zavrsniY);
    }elsif ($nagibPravca < 1){
        &crtajLinijuKutDo45($pocetniX, $pocetniY, $zavrsniX, $zavrsniY
+);
    }elsif ($nagibPravca > 1){
        &crtajLinijuKutDo90($pocetniX, $pocetniY, $zavrsniX, $zavrsniY
+);
    }
}

#*********************************************
#    Mis.
#*********************************************

sub myMouse{
    
    my ($button, $state, $x, $y) = @_;
    #    Lijeva tipka - crta pocetnu tocku ili liniju.
    if ($button == GLUT_LEFT_BUTTON and $state == GLUT_DOWN){
        #    Pamti krajnju tocke linije.
        $Lx[$Ix] = $x;
        $Ly[$Ix] = $sub_height - $y;
        $Ix = ($Ix+1)%2;
        
        printf("Koordinate tocke %d: %d %d \n", $Ix+1, $x, $y);
        #    Crta prvu tocku ili liniju do druge tocke.
        if ($Ix == 0) {&myLine($Lx[0], $Ly[0], $Lx[1], $Ly[1]);}
        #else            glVertex2i(x, sub_height-y);
        
        
        
        glFlush();
    }
    
    #    Desna tipka - brise canvas. 
    elsif ($button == GLUT_RIGHT_BUTTON and $state == GLUT_DOWN)
    {
        &myReshape($sub_width, $sub_height);
    }
}


#****************************************************
#    Tastatura tipke - r, g, b, k - mijenjaju boju.
#****************************************************

sub myKeyboard{
    my ($theKey, $mouseX, $mouseY) = @_;
    $theKey eq 'r' and glColor3f(1,0,0);
    $theKey eq 'g' and glColor3f(0,1,0);
    $theKey eq 'b' and glColor3f(0,0,1);
    $theKey eq 'k' and glColor3f(0,0,0);
    print "tipka $theKey\n";
    glRecti($sub_width-15, $sub_height-15, $sub_width, $sub_height);
    glFlush();
}
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