#!/usr/bin/perl -w
# Generate PNG files that shows the input text being rotated 90
# degrees clockwise.

use strict;
use File::Temp;

use constant PI => atan2(0, -1);
use constant FRAMES => 20;
use constant PAGE_OFFSET_X => 306;
use constant PAGE_OFFSET_Y => 396;
use constant CANVAS_WIDTH => 400;
use constant FONT_SCALE_FACTOR => 1.2;

use constant CROP_X => 275;
use constant CROP_Y => 650;
use constant CROP_S => 2000;
use constant RESIZE_WIDTH => 800;

# Load input
if( $#ARGV != 1 )
{
   die "$0 <input> <output_prefix>\n";
}
my ($input_text, $output_prefix) = @ARGV;

open my $infile, "<$input_text" or die $!;
my @lines = <$infile>;
close $infile;
my $width = 0;
foreach (@lines)
{
   chomp;
   $width = length($_) if $width < length($_);
}
my $height = scalar @lines;

# Compute offsets
my $cx = $width / 2;
my $cy = $height / 2;
my $long_edge = $width > $height ? $width : $height;
my $spacing = CANVAS_WIDTH / $long_edge;

# Generate frames
my $ps_file = tmpnam();
for(my $frame = 0; $frame < FRAMES; $frame++)
{
   # Page header
   my $scale = $spacing * FONT_SCALE_FACTOR;
   my $ps = '%!PS' .
            "\n/Courier-Bold findfont $scale scalefont setfont\n";

   # Compute angle, using a cubic to make the rotation accelerate
   # at the beginning and decelerate at the end.
   #
   # f(x) = -2x^3 + 3x^2
   # f'(x) = -6x^2 + 6x
   #  -> f(0) = 0
   #  -> f(1) = 1
   #  -> f'(0) = 0
   #  -> f'(1) = 0
   my $ax = $frame / FRAMES;
   my $ay = -2 * ($ax * $ax * $ax) + 3 * ($ax * $ax);
   my $angle = $ay * -PI / 2;

   # Transpose and draw each character.
   #
   # Note that PostScript renders each character at their bottom left
   # corners, but we really want to render them at the center so that
   # the rotated characters will be aligned between animation segments.
   # This is achieved by adjusting the character offsets with
   # "$spacing/2" before the rotation is done so that we rotate from
   # the center, minus another "$spacing/2" after rotation so that we
   # render characters at their centers.
   for(my $y = 0; $y < $height; $y++)
   {
      my $dy = ($cy - $y) * $spacing - $spacing / 2;
      for(my $x = 0; $x < $width; $x++)
      {
         # No need to render spaces
         next if $x >= length($lines[$y]);
         my $c = substr($lines[$y], $x, 1);
         next if $c eq " ";

         # Escape special characters for PostScript
         if( $c =~ /[()\\]/ )
         {
            $c = '\\' . $c;
         }

         my $dx = ($x - $cx) * $spacing + $spacing / 2;

         my $px = cos($angle) * $dx - sin($angle) * $dy + PAGE_OFFSET_X -
                  $spacing / 2;
         my $py = sin($angle) * $dx + cos($angle) * $dy + PAGE_OFFSET_Y +
                  $spacing / 2;
         $ps .= "$px $py moveto ($c) show\n";
      }
   }

   # Page footer
   $ps .= "showpage\nquit\n";

   # Write PostScript file
   open my $outfile, ">$ps_file" or die $!;
   print $outfile $ps;
   close $outfile;

   # Convert PostScript to PPM
   my $cmd = "gs -q -dBATCH -dNOPAUSE -sDEVICE=ppmraw " .
             "-r300x300 -dTextAlphaBits=4 -dGraphicsAlphaBits=4 " .
             "-sOutputFile=${output_prefix}_tmp.ppm $ps_file";
   system $cmd;

   # Crop and resize output
   $cmd = sprintf 'pamcut -left %d -top %d -width %d -height %d ' .
                  '%s_tmp.ppm ' .
                  ' | pnminvert ' .
                  ' | pamscale -xsize %d ' .
                  ' | pnmtopng -compression 9 > %s%04d.png',
                  CROP_X, CROP_Y, CROP_S, CROP_S,
                  $output_prefix,
                  RESIZE_WIDTH,
                  $output_prefix,
                  $frame;
   system $cmd;
}
unlink "${output_prefix}_tmp.ppm";
unlink $ps_file;