perl-opengl椭圆算法

孤独海岸线

#!/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 $xcenter=5;
my $ycenter=2;
my $Rx=16;
my $Ry=69;
my $Rx2=$Rx*$Rx;
my $Ry2=$Ry*$Ry;  
my $twoRx2=2*$Rx2;
my $twoRy2=2*$Ry2;
my $p;
my $x=0;
my $y=$Ry;
my $px=0;
my $py=$twoRx2*$y;
glPointSize(1);
glColor3f(255,0,255);  
&showpoints($xcenter,$ycenter,$x,$y);
$p=round($Ry2-($Rx2*$Ry)+(0.25*$Rx2));
for (;$px<$py;$x++)
{
$px+=$twoRy2;
if ($p<0)
{
$p+=$Ry2+$px;
}
else
{
$y--;
$py-=$twoRx2;
$p+=$Ry2+$px-$py;
}
&showpoints($xcenter,$ycenter,$x,$y);
}
$p=round($Ry2*(($x+0.5)**2)+$Rx2*(($y-1)**2)-$Rx2*$Ry2);
for (;$y>0;$y--)
{
$py-=$twoRx2;
if ($p>0)
{
$p+=$Rx2-$py;
}
else
{
$x++;
$px+=$twoRy2;
$p+=$Rx2-$py+$px;
}
&showpoints($xcenter,$ycenter,$x,$y);
}
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();
}
sub showpoints()
{
my ($xcenter,$ycenter,$x,$y)=@_;
glBegin(GL_POINTS);
glVertex2f($xcenter+$x,$ycenter+$y);
glVertex2f($xcenter-$x,$ycenter+$y);
glVertex2f($xcenter+$x,$ycenter-$y);
glVertex2f($xcenter-$x,$ycenter-$y);
glEnd();
}
sub round()
{
return  int($_[0]+0.5);
}