Animating build progress on a Minecraft server

My Minecraft server is seeing some use again, and I decided to build a life size model of the Philadelphia Museum of Art. I also thought it would be cool to have an animated gif of the build progress as things go.

Configuring Overviewer

We use Minecraft Overviewer to generate Google-maps style views of our world for the web. I created a config file limiting the render area to the coordinates around the building

worlds["Main"] = "/minecraft/Minecraft/world"

renders["normalrender"] = {
        "world": "Main",
        "title": "Overworld",
        "dimension": "overworld",
        "crop" : (200, -90, 420, 70),
}
outputdir="/minecraft/renders/museum"

Compositing the tiles
I found a script for making composites from google map data, originally written for use with Overviewer, but it was pretty far out of date and written for a different version of python than what I’ve got installed. I used it as a jumping off point for writing my own composite script.

#!/usr/bin/env python

import Image, ImageChops

import os, fnmatch
import os.path
import re

import sys

CHUNK_SIZE = 384

def trim(im):
    bg = Image.new(im.mode, im.size, im.getpixel((0,0)))
    diff = ImageChops.difference(im, bg)
    diff = ImageChops.add(diff, diff, 2.0, -100)
    bbox = diff.getbbox()
    if bbox:
        return im.crop(bbox)

def find_files(directory, pattern):
    regex = re.compile(pattern)
    for root, dirs, files in os.walk(directory):
        for basename in files:
            if regex.match(basename):
                filename = os.path.join(root, basename)
                yield filename

def getAllFiles(srcdir):
  return find_files(srcdir,  "[0-9]+.png")

def getCoordinates(f):
  return map(lambda x: int(x), re.findall(r'[0-9-]+', f))

def getX(c):
  return {
    0: 0,
    1: 1,
    2: 0,
    3: 1,
  }[c]

def getY(c):
  return {
    0:0,
    1:0,
    2:1,
    3:1,
  }[c]

if len(sys.argv) != 4:
  print "Usage:", sys.argv[0], "<source directory (Dir)> <output file> <zoom level>"
  sys.exit(1)

sourceDirectory = sys.argv[1]
zoomLevel = int(sys.argv[3])
outputName = sys.argv[2]

width = (2**zoomLevel)  * CHUNK_SIZE
height = (2**zoomLevel)  * CHUNK_SIZE
print "Width:", width, "Height:", height

output = Image.new("RGBA", (width, height))

for f in getAllFiles(sourceDirectory):
  coords = getCoordinates(f)
  if len(coords) == zoomLevel:
    chunk = Image.open(os.path.join(sourceDirectory, f))
    #print chunk
    xbin = ""
    ybin = ""
    for c in coords:
      xbin = xbin + str(getX(c))
      ybin = ybin + str(getY(c))
    y = int(ybin,2)
    x = int(xbin,2)
    output.paste(chunk, (x*CHUNK_SIZE, y*CHUNK_SIZE))

print "Map merged, saving..."

output = trim(output)

if outputName[-3:] == "jpg" or outputName[-4:] == "jpeg":
  output.save(outputName, quality=100)
else:
  try:
    output.save(outputName, quality=85, progressive=True, optimize=True)
  except:
    print "Error saving with progressive=True and optimize=True, trying normally..."
    output.save(outputName, quality=85)

print "Done!"

This generates a daily snapshot and puts it in a web-accessible folder. I can then make a gif of all the images in that folder with ImageMagick’s convert utility
convert -delay 80 -loop 0 *jpg animated.gif

Checking for modifications
Originally I ran the script once daily on a cron, but later decided to run the world generator every half hour and only generate an image if there’s something new to see.

#!/bin/bash

rendersecs=$(expr `date +%s` - `stat -c %Y /minecraft/renders/museum/normalrender/3/`)
snapsecs=$(expr `date +%s` - `stat -c %Y /minecraft/renders/museum/last-snapshot`)
if [ "$rendersecs" -lt "$snapsecs" ]; then
  echo "Render was modified $rendersecs secs ago. Last snapshot $snapsecs secondds ago. Updating snapshot."
  /minecraft/renders/merge.py /minecraft/renders/museum /var/www/html/museum/$(date +\%Y-\%m-\%d-\%H\%M).jpg 3
  touch -m /minecraft/renders/museum/last-snapshot
  convert -delay 40 -loop 0 /var/www/html/museum/*jpg /var/www/html/museum/animated.gif
fi

Setting up cron tasks
I put two new jobs in my crontab file: one to generate the terrain and one to run my shell script. I give Overviewer a bit of a head start in case it has a lot of work to do.

*/30 *  * * *  overviewer.py --conifg=/minecraft/overviewer-museum.conf
10,40 *  * * *  /minecraft/update-museum.sh