X-mas tree

for http://codegolf.stackexchange.com/questions/15860/

HTML

<canvas id=c width=200 height=300 style="display:none"></canvas>
<div id=config></div>

JavaScript

////////////////////////////////////////////////////////////////////////////////
var TAU = 2*Math.PI,
    deg = TAU/360,
    
    TRUNK_VIEW      = {lineWidth:3, strokeStyle: "brown", zIndex: 1},
    BRANCH_VIEW     = {lineWidth:1, strokeStyle: "green", zIndex: 2},
    TRUNK_SPACING   = 1.5,
    TRUNK_BIAS_STR  = -0.5,
    TRUNK_SLOPE     = 0.25,
    BRANCH_LEN      = 1,
    BRANCH_P        = 0.01,
    MIN_SLOPE       = -5*deg,
    MAX_SLOPE       = 20*deg,
    INIT_SLOPE      = 10*deg,
    MAX_D_SLOPE     =  5*deg,
    DIR_KEEP_BIAS   = 10,
    GROWTH_MSPF     = 10, //ms per frame
    GROWTH_TPF      = 10, //ticks per frame
    ROTATE_MSPF     = 10,
    ROTATE_RPF      = 1*deg; //radians per frame

var configurables = [
//    {key: "TRUNK_SPACING", name: "Branch spacing", widget: "number",
//     description: "Distance between main branches on the trunk, in pixels"},
    {key: "TRUNK_BIAS_STR", name: "Branch distribution", widget: "number",
     description: "Angular distribution between nearby branches. High values tend towards one-sided trees, highly negative values tend towards planar trees. Zero means that branches grow in independent directions."},
    {key: "TRUNK_SLOPE", name: "Trunk slope", widget: "number",
     description: "Amount of horizontal movement of the trunk while growing"},
    {key: "BRANCH_P", name: "Branch frequency", widget: "number",
     description: "Branch frequency - if =1/100, a single twig will branch off approximately once per 100 px"},
    {key: "MIN_SLOPE", name: "Minimum slope", widget: "number", scale: deg,
     description: "Minimum slope of a branch, in degrees"},
    {key: "MAX_SLOPE", name: "Maximum slope", widget: "number", scale: deg,
     description: "Maximum slope of a branch, in degrees"},
    {key: "INIT_SLOPE", name: "Initial slope", widget: "number", scale: deg,
     description: "Angle at which branches leave the trunk"},
    {key: "DIR_KEEP_BIAS", name: "Directional inertia", widget: "number",
     description:...