perl-opengl-直线绘制

#!/usr/bin/perl -w
use strict;
use warnings;
use OpenGL qw/ :all /;
use OpenGL::Config;   

glutInit();
glutInitDisplayMode(GLUT_RGB|GLUT_SINGLE);
glutInitWindowPosition(100,100);
glutInitWindowSize(400,400);
glutCreateWindow("my  OpenGL program");
glClearColor(0,0,0,255);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
gluOrtho2D(-100,100,-100,100);
glutDisplayFunc(\&mydis);
glutMainLoop();
return 0;

sub mydis()
{
  my $x0=-100;
  my $y0=-85;  
  my $xend=93;
  my $yend=26;
  my $dx=abs($xend-$x0);
  my $dy=abs($yend-$y0);
  my $p=2*$dy-$dx;
  my $twoDy=2*$dy;
  my $twoDyMinusDx=2*($dy-$dx);
  my $x;
  my $y;
  glPointSize(1);
  glColor3f(255,0,255);  
  if ($x0>$xend)
  {
     $x=$xend;
	 $y=$yend;
	 $xend=$x0;
  }
  else
  {
     $x=$x0;
	 $y=$y0;
  }
  glBegin(GL_POINTS);
  glVertex2f($x,$y);	
  glEnd();  
  glFlush(); 
  for (;$x<$xend;$x++)
  {
    if ($p<0)
	{
	   $p+=$twoDy;
	}
	else
	{
	   $y++;
	   $p+=$twoDyMinusDx;
	}
    glBegin(GL_POINTS);
    glVertex2f($x,$y);	
    glEnd();  	
  }
  glFlush();
  glColor3f(0,255,0);
  glBegin(GL_LINES);
  glVertex2f(-100,0);
  glVertex2f(100,0); 
  glEnd();
  glBegin(GL_LINES);
  glVertex2f(0,-100);
  glVertex2f(0,100); 
  glEnd();  
  glFlush();
}