#!/usr/local/bin/perl
#
# teapotgif.pl : make an animated gif image of a rotating teapot
# (c) 2013 jl_morel@bribes.org - http://http://bribes.org/perl
use strict;
use warnings;
use OpenGL qw/ :all /;
use OpenGL::Image;
use Image::Magick;

my $animatedgifname = "teapot.gif";
my $animatedgif     = Image::Magick->new();

my @light0_position    = ( 2.0,  8.0,  2.0,  0.0 );
my @light_diffuse      = ( 1.0,  1.0,  1.0,  1.0 );
my @light_ambient      = ( 0.15, 0.15, 0.15, 0.15 );
my @mat_amb_diff_color = ( 0.4,  0.2,  0.8,  1.0 );

#------ Initialization routine

sub init {
  glClearColor( 1, 1, 1, 1 );    # White background
  glShadeModel(GL_SMOOTH);       # Smooth shading
  glEnable(GL_DEPTH_TEST);       # Enable hidden surface removal
  glEnable(GL_MULTISAMPLE);      # Enable multisample antialiasing
  glEnable(GL_LIGHTING);         # Enable lighting
  glEnable(GL_LIGHT0);
  glLightfv_p( GL_LIGHT0, GL_POSITION, @light0_position );
  glLightfv_p( GL_LIGHT0, GL_DIFFUSE,  @light_diffuse );
  glLightfv_p( GL_LIGHT0, GL_AMBIENT,  @light_ambient );
  glMaterialfv_p( GL_FRONT, GL_AMBIENT_AND_DIFFUSE, @mat_amb_diff_color );
  glEnable(GL_CLIP_PLANE0);      # One clip plane needed
}

#------ Draw the teapot

my $size = 3.5;                  # teapot size
my $spin = 0;                    # rotation angle

sub display {
  glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

  glLoadIdentity();
  gluLookAt( 2.0, 4.0, 10.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0 );
  glPushMatrix();
  glRotatef( $spin, 0.0, 1.0, 0.0 );

  # The plane equation is 0x+0y+1z=0 with normal vector (0,0,1)
  glClipPlane_p( GL_CLIP_PLANE0, 0, 0, 1, 0 );
  glutSolidTeapot($size);

  # Same plane but with normal vector (0,0,-1)
  glClipPlane_p( GL_CLIP_PLANE0, 0, 0, -1, 0 );
  glutWireTeapot($size);

  glPopMatrix();
  glutSwapBuffers();
}

#------ GLUT Callback called when the window is resized

sub reshape {
  my ( $w, $h ) = @_;
  glViewport( 0, 0, $w, $h );
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluPerspective( 45.0, $h ? $w / $h : 0, 1.0, 20.0 );
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

#------ Routine for rotating the teapot

my $WaitUntil = 0;

sub spinDisplay {
  my $TimeNow = glutGet(GLUT_ELAPSED_TIME);
  if ( $TimeNow >= $WaitUntil ) {
    $spin += 1.0;
    if ( $spin > 360 ) {

      # 10/100ths of a second between images, loop indefinitely
      $animatedgif->Set( delay => 10, loop => 0 );
      $animatedgif->Write($animatedgifname);
      unlink "tmp.gif";
      exit;
    }
    if ( $spin % 5 == 0 ) {    # One capture every 5 degree
      IMCapture("tmp.gif");    # Save as gif image
      $animatedgif->Read("tmp.gif");
    }
    glutPostRedisplay();
    $WaitUntil = $TimeNow + 1000 / 25;    # 25 frames/s
  }
}

#------ Main

glutInit();
glutInitDisplayMode(
  GLUT_DOUBLE                             # Double buffering
    | GLUT_RGB                            # RGB color mode
    | GLUT_DEPTH                          # Hidden surface removal
    | GLUT_MULTISAMPLE                    # Multisample antialiasing
);
glutInitWindowSize( 420, 240 );
glutCreateWindow("Teapot");
init();
glutDisplayFunc( \&display );
glutReshapeFunc( \&reshape );
glutIdleFunc( \&spinDisplay );
glutMainLoop();

#------ Image capture function with ImageMagick
# Usage: IMCapture( $imgname [, $x, $y, $width, $height ] );
# $imgname is the image name with extension (.gif, .jpeg, .png ...)
# The optional part [ $x, $y, $width, $height ] defines  the dimensions
# of the rectangle to capture.
# If not supplied, the dimensions of the current window are used.

sub IMCapture {
  my $file = shift;
  my ( $x, $y, $width, $height ) = @_ == 4 ? @_ : glGetIntegerv_p(GL_VIEWPORT);
  my $img = new OpenGL::Image(
    engine => 'Magick',
    width  => $width,
    height => $height
  );
  my ( $def_fmt, $def_type ) = $img->Get( 'gl_format', 'gl_type' );
  glFinish();
  glReadPixels_c( $x, $y, $width, $height, $def_fmt, $def_type, $img->Ptr() );
  $img->Save($file);
}