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branching.js
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branching.js
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var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
//Lets resize the canvas to occupy the full page
var W = window.innerWidth;
var H = window.innerHeight;
canvas.width = W;
canvas.height = H;
var makeBranch = function(mouseCoords){
//Some variables
var length, divergence, reduction, line_width, start_points = [];
init();
function init() {
//let's draw the trunk of the tree
//let's randomise the variables
//length of the trunk - 100-150
length = 200 + Math.round(Math.random()*50);
//angle at which branches will diverge - 10-60
divergence = 10 + Math.round(Math.random()*170);
//Every branch will be 0.75times of the previous one - 0.5-0.75
//with 2 decimal points
reduction = Math.round(54 + Math.random()*20)/100;
//width of the branch/trunk
line_width = Math.round(Math.random() * 10);
//This is the end point of the trunk, from where branches will diverge
var first_start_points = make_trunk();
var trunk = {x: mouseCoords.x, y: mouseCoords.y, angle: 90};
branches(first_start_points);
}
function make_trunk() {
var trunk = {x: mouseCoords.x, y: mouseCoords.y, angle: 90};
//It becomes the start point for branches
var start_points = []; //empty the start points on every init();
start_points.push(trunk);
return start_points;
}
//Lets draw the branches now
function branches(start_points) {
//reducing line_width and length
length = length * reduction;
line_width = line_width - Math.round(Math.random() * 10);
ctx.lineWidth = line_width;
var new_start_points = [];
ctx.beginPath();
for(var i = 0; i < start_points.length; i++)
{
var sp = start_points[i];
//2 branches will come out of every start point. Hence there will be
//2 end points. There is a difference in the divergence.
var ep1 = get_endpoint(sp.x, sp.y, sp.angle+divergence, length);
var ep2 = get_endpoint(sp.x, sp.y, sp.angle-divergence, length);
//drawing the branches now
ctx.moveTo(sp.x, sp.y);
ctx.lineTo(ep1.x, ep1.y);
ctx.moveTo(sp.x, sp.y);
ctx.lineTo(ep2.x, ep2.y);
//Time to make this function recursive to draw more branches
ep1.angle = sp.angle+divergence;
ep2.angle = sp.angle-divergence;
new_start_points.push(ep1);
new_start_points.push(ep2);
}
// randomize color
var rgb = hsv_to_rgb(Math.random(), Math.random(), 0.95);
ctx.strokeStyle = "rgb(" + rgb.r + ", " + rgb.g + ", " + rgb.b + ")";
ctx.stroke();
//recursive call - only if length is more than 2.
//Else it will fall in an long loop
if (length > 2) {
window.setTimeout(function() {branches(new_start_points)}, 50);
}
}
function get_endpoint(x, y, a, length) {
//This function will calculate the end points based on simple vectors
//http://physics.about.com/od/mathematics/a/VectorMath.htm
//You can read about basic vectors from this link
var epx = x + length * Math.cos(a*Math.PI/180);
var epy = y + length * Math.sin(a*Math.PI/180);
return {x: epx, y: epy};
}
};
canvas.addEventListener("mousedown", function(clickEvent) {
var mouseCoords = relMouseCoords(clickEvent, canvas);
makeBranch(mouseCoords);
});
var clearButton = document.getElementById("clear");
clearButton.addEventListener("click", function() {
ctx.fillStyle = "white";
ctx.fillRect(0, 0, W, H);
});
var relMouseCoords = function(clickEvent, el){
var totalOffsetX = 0;
var totalOffsetY = 0;
var canvasX = 0;
var canvasY = 0;
do{
totalOffsetX += el.offsetLeft;
totalOffsetY += el.offsetTop;
}
while(el = el.offsetParent)
canvasX = clickEvent.pageX - totalOffsetX;
canvasY = clickEvent.pageY - totalOffsetY;
return {x:canvasX, y:canvasY}
}
var hsv_to_rgb = function(h, s, v) {
var h_i = parseInt(h*6);
var f = h*6 - h_i;
var p = v * (1 - s);
var q = v * (1 - f*s);
var t = v * (1 - (1 - f) * s);
var r;
var g;
var b;
if (h_i==0) {
r = v;
g = t;
b = p;
}
if (h_i==1) {
r = q;
g = v;
b = p;
}
if (h_i == 2) {
r = p;
g = v;
b = t;
}
if (h_i == 3) {
r = p;
g = q;
b = v;
}
if (h_i == 4) {
r = t;
g = p;
b = v;
}
if (h_i == 5) {
r = v;
g = p;
b = q;
}
return {r: parseInt(r * 256), g: parseInt(g * 256), b: parseInt(b * 256)};
};