Sample 2

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#	This program generates a rainbow spectrum,
#	and also plots the individual components.

import piddle
import math

def makeCanvas():
	"Create a Canvas object."
	import piddleQD
	return piddleQD.QDCanvas()
	
def plot(f,canvas,offset=0):
	for i in range(0,100):
		x = float(i)/100
		canvas.drawLine(i*3+offset,250, i*3+offset,250-100*f(x))

def showColors(colors):
	global canvas
	try:
		canvas.clear()
	except:
		canvas = makeCanvas()

	# draw a black background for the spectrum
	canvas.drawRect( 0,0,300,100, edgeColor=piddle.black, fillColor=piddle.black )

	# draw the spectrum
	for i in range(len(colors)):
		canvas.drawLine(i,20,i,80, colors[i])

	# plot the components of the spectrum
	canvas.defaultLineColor = piddle.red
	plot(redfunc, canvas)

	canvas.defaultLineColor = piddle.blue
	plot(bluefunc, canvas, 1)

	canvas.defaultLineColor = piddle.green
	plot(greenfunc, canvas, 2)

	# update the canvas
	canvas.flush()

def bluefunc(x):
	return 1.0 / (1.0 + math.exp(-10*(x-0.6)))


def redfunc(x):
	return 1.0 / (1.0 + math.exp(10*(x-0.5)))

	return out

def greenfunc(x):
	return 1 - pow(redfunc(x+0.2),2) - bluefunc(x-0.3)

def genColors(n=100):
	out = [None]*n;
	for i in range(n):
		x = float(i)/n
		out[i] = piddle.Color(redfunc(x), greenfunc(x), bluefunc(x));
	return out

showColors(genColors(300))