#! /usr/bin/perl

if(@ARGV != 4) {
    print STDERR "Usage:  $0  STEMNAME  FOVY  TILEXSIZExTILEYSIZE  NXxNY
Records the partiview view as a series of images,
chopped into NXxNY tiles of TILEXSIZExTILEYSIZE pixels each,
with overall Y-axis field of view FOVY,
as a series of images named STEMNAME.XX.YY.ppm
for 00 <= XX <= NX-1, 00 <= YY <= NY-1.  YY=00 at top.

Sorry you have to specify the angular field of view FOVY,
which this script can't determine on its own;
use partiview's \"fovy\" command to discover the current setting.

Also prints to stderr some advice you might use to rejoin the
tiled pieces into a whole, using pnmcat from the netpbm package.
";
    exit(1);
}

$stemfmt = $ARGV[0];
if($stemfmt !~ /\%.*\%/) {
    $stemfmt .= "." unless $stemfmt =~ m'/$';
    $stemfmt .= "%02d.%02d.ppm";
}

$fovy = $ARGV[1];

($xpix, $ypix) = ($ARGV[2] =~ m'(\d+)\D*(\d*)$');
$ypix = $xpix if $ypix eq "";

($xtiles, $ytiles) = ($ARGV[3] =~ m'(\d+)\D*(\d*)$');
$ytiles = $xtiles if $ytiles eq "";

unless($xpix > 10 && $ypix > 10) {
    print STDERR "$0: Expected reasonable tile size (XSIZExYSIZE or SIZE in pixels), not $ARGV[2]\n";
    exit(1);
}

unless($xtiles > 0 && $ytiles > 0) {
    print STDERR "$0: Expected reasonable tile count (NXxNY or N), not $ARGV[3]\n";
    exit(1);
}


sub say {
    $| = 1;

    print join("\n", @_), "\n";
}

sub tandeg {
    my($deg) = @_;
    my($rad) = $deg / 57.29579;
    sin($rad) / cos($rad);
}

sub atandeg {
    57.29579 * atan2( $_[0], 1 );
}

&say("eval winsize ${xpix}x${ypix}");
&say("eval update");
&say("eval async sleep 1");

# Assuming square pixels, compute tan-half-fov in each direction.

$thfovy = &tandeg( $fovy / 2 );
$thfovx = (($xpix*$xtiles) / ($ypix*$ytiles)) * $thfovy;

sub xwindow {	# 0 .. xtiles => -$thfovx .. $thfovx
   my($tileno) = @_;
   &atandeg( $thfovx * (($tileno/$xtiles)*2 - 1) );
}

sub ywindow {	# 0 .. xtiles => -$thfovx .. $thfovx
   my($tileno) = @_;
   &atandeg( $thfovy * (($tileno/$ytiles)*2 - 1) );
}

# Loop over tiles
    
for($yy = 0; $yy < $ytiles; $yy++) {
    for($xx = 0; $xx < $xtiles; $xx++) {
	&say( sprintf("eval subcam tiler  0 90 0  %.5g %.5g  %.5g %.5g",
		-&xwindow($xx),		  &xwindow($xx+1),
		-&ywindow($ytiles-$yy-1), &ywindow($ytiles-$yy) ),
	     "eval update" );

	&say( sprintf("eval snapshot $stemfmt", $xx, $yy),
	     "eval update" );
    }
}
&say("eval subcam off");


($justystem = $stemfmt) =~ s/\%.*/\%02d.ppm/;
($resultfile = $stemfmt) =~ s/\%.*/all.ppm/;

print STDERR "\n# Now to assemble these, you could use:\n";
@ytemps = ();
for($yy = 0; $yy < $ytiles; $yy++) {
    print STDERR "pnmcat -lr";
    for($xx = 0; $xx < $xtiles; $xx++) {
	printf STDERR " $stemfmt", $xx, $yy;
    }
    $ytemp = sprintf($justystem, $yy);
    printf STDERR " > $ytemp\n";
    push(@ytemps, $ytemp);
}
print STDERR join(" ", "pnmcat -tb", @ytemps), " > $resultfile\n";
print STDERR join(" ", "rm", @ytemps), "\n";
print STDERR "\n";