#!/usr/bin/perl -w

# http://www.hewgill.com/galilean-thermometer/index.html
# This program creates a figure for use in the above page.
# Requires:
#   GD.pm - http://stein.cshl.org/WWW/software/GD/GD.html
#   libgd - http://www.boutell.com/gd/

use GD;

$img = new GD::Image(260, 360) or die;
$white = $img->colorAllocate(255,255,255);
$black = $img->colorAllocate(0,0,0);
$blue  = $img->colorAllocate(0,0,128);
$green = $img->colorAllocate(0,128,0);
$orange= $img->colorAllocate(224,128,0);
$red   = $img->colorAllocate(192,0,0);

$img->interlaced('true');

$hatch = new GD::Image(5,5);
$hatch->transparent($hatch->colorAllocate(255,255,255));
$hatch->line(0,4,4,0,$hatch->colorAllocate(0,0,0));
$img->setTile($hatch);

$vessel = new GD::Polygon;
$vessel->addPt(0,0);
$vessel->addPt(0,320);
$vessel->addPt(100,320);
$vessel->addPt(100,0);
$vessel->addPt(90,0);
$vessel->addPt(90,310);
$vessel->addPt(10,310);
$vessel->addPt(10,0);

$bulb = new GD::Polygon;
$bulb->addPt(15,30);
$bulb->addPt(30,30);
$bulb->addPt(30,0);
$bulb->addPt(0,0);
$bulb->addPt(0,30);
$bulb->addPt(15,30);
$bulb->addPt(15,32);
$bulb->addPt(25,32);
$bulb->addPt(25,43);
$bulb->addPt(5,43);
$bulb->addPt(5,32);
$bulb->addPt(15,32);

sub deg {
  my ($x,$y,$c) = @_;
  $img->setPixel($x+1,$y,$c);
  $img->setPixel($x+2,$y,$c);
  $img->setPixel($x+3,$y+1,$c);
  $img->setPixel($x+3,$y+2,$c);
  $img->setPixel($x+2,$y+3,$c);
  $img->setPixel($x+1,$y+3,$c);
  $img->setPixel($x,$y+2,$c);
  $img->setPixel($x,$y+1,$c);
}

sub bulb {
  my ($x,$y,$f,$t,$c) = @_;
  $bulb->offset($x,$y);
  $img->polygon($bulb,$black);
  $img->filledRectangle($x+1,$y+$f,$x+29,$y+29,$c);
  $img->string(gdSmallFont,$x+8,$y+31,$t,$black);
  deg($x+20,$y+34,$black);
  $bulb->offset(-$x,-$y);
}

$vessel->offset(10,30);
  $img->filledPolygon($vessel,gdTiled);
  $img->polygon($vessel,$black);
  $vessel->offset(-10,-30);

$img->line(20,40,100,40,$black);
$img->string(gdSmallFont,50,10,"76 F",$black);
deg(63,13,$black);

bulb(45,40,17,"80",$blue);
bulb(45,105,16,"76",$green);
bulb(45,205,15,"72",$orange);
bulb(45,250,14,"68",$red);
bulb(45,295,13,"64",$blue);

$vessel->offset(150,30);
  $img->filledPolygon($vessel,gdTiled);
  $img->polygon($vessel,$black);
  $vessel->offset(-150,-30);

$img->line(160,40,240,40,$black);
$img->string(gdSmallFont,190,10,"70 F",$black);
deg(203,13,$black);

bulb(185,40,17,"80",$blue);
bulb(185,85,16,"76",$green);
bulb(185,130,15,"72",$orange);
bulb(185,250,14,"68",$red);
bulb(185,295,13,"64",$blue);

$fn = $0;
$fn =~ s/pl$/png/;
open(F, ">$fn") or die;
binmode F;
print F $img->png;
close(F);