Living Code

There is a lot of interesting stuff happening in Javascript land these days, even to the point of other languages targetting the browser as a runtime, but running on top of Javascript. You can run Scheme right in the browser, and by now everyone has probably heard of Objective-J (open-source coming soon), an Objective-C-like language used by 280 North to create their 280 Slides web application, inspired by Apple's Keynote.

Since my last post about Processing, John Resig managed to port most of Processing to Javascript, so it is easier than ever to get started. Now instead of having to download the Java-based runtime, you can create Processing animations in your browser, within the limitations that it only targets very recent, beta browsers (Firefox 3, Opera 9.5, WebKit nightlies, no version of IE) and that not all of Processing is supported (no 3D, for instance, and my example from the earlier post does not run). Still, it is interesting and a lot of fun to play with. My seven-year-old son is fascinated with computer programming and looking to move beyond Scratch, so as part of that I stuck all the basic examples from Mr. Resig's site into one page, with a menu to select them, and a button to run them. And I made them editable. You can write entirely new code too, of course, but the examples can help for getting started. I hope folks enjoy it.

Processing Playground

Of course, what my kids really want is a version of Scratch that we can extend to add some more features of our own. Scratch has been open-sourced, so we could possibly extend it, but it is built on Squeak Smalltalk, and I've never been very good at Smalltalk. Instead, I am porting it to Javascript. It is still in the early stages, but I'm making steady progress in my hour or so I have to code each evening, and my kids are eager to use it, so they keep me motivated and focussed.

Just for fun, and because I'm trying out two things:

1. Using Ecto for posting again
2. Blogging more often

Here are my results from the latest craze:

$ history|awk '{a[$2]++} END{for(i in a){printf "%5d\t%s\n",a[i],i}}'|sort -rn|head
139 ls
87 cd
54 python
43 /usr/bin/python
38 less
21 vim
16 clear
12 mate
11 rm
10 ssh

The first python is the one I built from source so I can include it in applications packaged with py2app, the second is the built-in python for Leopard. Both are version 2.5. The mate program is used to open files in TextMate from the command line.

Just a reminder for Pythonistas in the Vancouver area: The Vancouver Python and Zope user group (VanPyZ) is tomorrow (Tuesday, April 1). Paul Prescod will be talking about metaprogramming in Python. Details and directions are on the VanPyZ site. And, as usual, we'll be heading out to the pub afterwards for more discussion.

Hope to see you there!

The latest version, 1.8, of PyGame can save PNGs directly from a Surface: pygame.Image.save(mySurface, 'myimagefile.png'). But what if you want to support an older version of PyGame, such as the one available for the N800 or the XO? Well, assuming you have access to the Python Image Library, you can use that:

import Image # from PIL
import pygame

def pygame_to_pil_img(pg_surface):
    imgstr = pygame.image.tostring(pg_surface, 'RGB')
    return Image.fromstring('RGB', pg_surface.get_size(), imgstr)

def pil_to_pygame_img(pil_img):
    imgstr = pil_img.tostring()
    return pygame.image.fromstring(imgstr, pil_img.size, 'RGB')

Once you have a PyGame Image, you can save it to PNG easily: myImage.save('myfilename.png')

I've found myself looking for this code snippet more than once, now I can Google for it more readily, and maybe someone else will find it helpful too.

The other day, Thomas Guest talked about drawing chessboards, and ended with a challenge. I wanted to answer a different challenge, however. What if, instead of drawing on a rectangular grid, we wanted to draw on a hexagonal grid? The following is my slapdash answer. For real-world use I'd make nice classes and pass more parameters to the methods, but to demonstrate the math I'm just going to use global constants and functions.

Like Thomas' article, I will show solutions using several different tools, in this case Apple's Core Graphics, PyGame, Python Imaging Library (PIL), and SVG. All of these solutions will use the same constants and math:

# Constants used by each solution

from math import sin, cos, pi, sqrt
THETA = pi / 3.0 # Angle from one point to the next
HEXES_HIGH = 8 # How many rows of hexes
HEXES_WIDE = 5 # How many hexes in a row
RADIUS = 30 # Size of a hex
HALF_RADIUS = RADIUS / 2.0
HALF_HEX_HEIGHT = sqrt(RADIUS ** 2 - HALF_RADIUS ** 2)
IMAGE_WIDTH = int(RADIUS * (HEXES_WIDE * 3 + .5))
IMAGE_HEIGHT = int(HALF_HEX_HEIGHT * (HEXES_HIGH + 1))

# Functions (generators) used by each solution

def hex_points(x,y):
    '''Given x and y of the origin, return the six points around the origin of RADIUS distance'''
    for i in range(6):
        yield cos(THETA * i) * RADIUS + x, sin(THETA * i) * RADIUS + y

def hex_centres():
    for x in range(HEXES_WIDE):
        for y in range(HEXES_HIGH):
            yield (x * 3 + 1) * RADIUS + RADIUS * 1.5 * (y % 2), (y + 1) * HALF_HEX_HEIGHT

Now, given the above, what does the code look like to draw the hexes? Because each library handles colours slightly differently, we will need a generator for colours (and we will need more than just black and white as the chessboard used, because each hex borders on six others). I haven't given a lot of thought to optimal colouring schemes: each colour generator simply produces red, yellow, blue, and green in a cycle. Here is the image produced by the Core Graphics solution, followed by the code:

def quartz_colours():
    while True:
        yield 1,0,0,1 # red
        yield 1,1,0,1 # yellow
        yield 0,0,1,1 # blue
        yield 0,1,0,1 # green

def quartz_hex():
    '''Requires a Mac with OS 10.4 or better and the Developer Tools installed'''
    import CoreGraphics as cg
    colours = quartz_colours()
    cs = cg.CGColorSpaceCreateDeviceRGB()
    c = cg.CGBitmapContextCreateWithColor(IMAGE_WIDTH, IMAGE_HEIGHT, cs, (0,0,0,.2))
    c.saveGState()
    c.setRGBStrokeColor(0,0,0,0)
    c.setLineWidth(0)
    for x,y in hex_centres():
        c.beginPath()
        c.setRGBFillColor(*colours.next())
        points = list(hex_points(x,y))
        c.moveToPoint(*points[-1])
        [c.addLineToPoint(*pt) for pt in points]
        c.drawPath(cg.kCGPathFill)
    c.restoreGState()
    c.writeToFile("quartz_hexes.png", cg.kCGImageFormatPNG)

Now for some cross-platform examples. Here is the image generated by PyGame, followed by that code:

def pygame_colours():
    while True:
        yield 255, 0, 0 # red
        yield 255, 255, 0 # yellow
        yield 0, 0, 255 # blue
        yield 0, 255, 0 # green

def pygame_hex():
    '''Requires PyGame 1.8 or better to save as PNG'''
    import pygame
    pygame.init()
    screen = pygame.display.set_mode((IMAGE_WIDTH, IMAGE_HEIGHT))
    colours = pygame_colours()
    for x,y in hex_centres():
        pygame.draw.polygon(screen, colours.next(), list(hex_points(x,y)))
    pygame.image.save(screen, 'pygame_hexes.png')

When you run the PyGame script, it will actually pop up a window very briefly, draw into the window, save the result, and close the window. I also didn't get the PyGame script to add transparency for the background, although I think it could be added fairly easily. Now, for the web, here is a solution in SVG, with the image captured by screenshot in Safari, followed by the Python code, and the resulting SVG code:

def svg_colours():
    while True:
        yield 'rgb(255, 0, 0)'
        yield 'rgb(255, 255, 0)'
        yield 'rgb(0, 0, 255)'
        yield 'rgb(0, 255, 0)'

def svg_hex():
    out = open('svg_hexes.svg', 'w')
    print >> out, '''<?xml version="1.0" standalone="no"?>
    <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
    <svg width="%spx" height="%spx" version="1.1" xmlns="http://www.w3.org/2000/svg">''' % (IMAGE_WIDTH, IMAGE_HEIGHT)
    colours = svg_colours()
    for pt in hex_centres():
        print >> out, '<polygon fill="%s" stroke-width="0" points="%s" />' % (colours.next(),  ' '.join(["%s,%s" % (x,y) for (x,y) in hex_points(*pt)]))
    print >> out, '</svg>'
    out.close()

And here is the SVG created by the above script: SVG Hexes

Finally, one library which overlaps with the ones used by the Chessboard example: Python Imaging Library.

pil_colours = pygame_colours  # same format works, so we'll re-use it

def pil_hex():
    import Image, ImageDraw
    image = Image.new("RGBA", (IMAGE_WIDTH,IMAGE_HEIGHT), (0,0,0,0))
    colours = pil_colours()
    draw = ImageDraw.Draw(image)
    for x,y in hex_centres():
        draw.polygon(list(hex_points(x,y)), fill=colours.next())
    image.save('pil_hexes.png', 'PNG')

That's it for my examples. Thomas ended with a challenge for displaying chess, and for describing the position. To describe the position, I would use a standard chess notation, such as described here. For my challenge, what other formats would be useful to create hex maps in? POVRay? Flash? Any other examples out there?