merge pixmap handling from sampler, material.h and ccdemos's image module to new Pixmap class
add check for PNG library, allow writing PNG file from a Pixmap
simplify demos using new methods from Sampler and Pixmap
from math import *def dot(a,b): sum = 0 for i in range(min(len(a),len(b))): sum += a[i]*b[i] return sumdef cross(a,b): return ( a[1]*b[2] - a[2]*b[1], a[2]*b[0] - a[0]*b[2], a[0]*b[1] - a[1]*b[0] )def unit(a): m = mag(a) return (a[0]/m, a[1]/m, a[2]/m)def mag(a): return sqrt(mag2(a))def mag2(a): return a[0]*a[0] + a[1]*a[1] + a[2]*a[2]