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fractal trees app js available as gist
/*The following vars are used for different parameters of generated tree and can searched easily:
mainBranch = the main generated branch
subBranches = the sub branches that are generated "infinitely"
travel = "distance" the branches will travel
branchWidth = Width of the stroke generated branches - keep in mind they
get exponentially thinner and thinner as recursion continues
startX, StartY, endX, endY = Defines path starting and ending values
length = length of each new tree relative to window size
angle = angle of path of each new tree
I annotated the code so you can follow along!
void function () {
//Declare variables travel, branchWidth, canvas, and the canvas context
var travel = 100 , branchWidth = 10
//Draw canvas and set 2D context
var canvas = document.getElementById('mycanvas')
var ctx = canvas.getContext('2d')
//set width and height of canvas to fill screen
canvas.width = window.innerWidth
canvas.height = window.innerHeight
var fractalTree = function () {
/* accesses clearRect() method of Canvas's 2d API with starting point (0,0) and size set to window.innerWidth
and .innerHeight
ctx.clearRect(0, 0, window.innerWidth, window.innerHeight)
//Defines placement of tree relative to window, also
drawTree(ctx, (window.innerWidth/2), (window.innerHeight/1), 40, -Math.PI/2, travel+10, branchWidth)
//Define drawTree var as function that has following variables as parameters
var drawTree = function (ctx, startX, startY, length, angle, travel, branchWidth) {
var rand = Math.random, dept,
newLength, newAngle,
mainBranch = 3,
endX, endY, maxAngle = Math.PI /2;
//Creates new canvas path
//Sets new trees to defined x and y coordinates - placed in center
ctx.moveTo(startX, startY)
//defines x and y end values by start values
endX = startX + length * Math.cos(angle)
endY = startY + length * Math.sin(angle)
//uses lineCap canvas property to round the lines
ctx.lineCap = 'round'
ctx.lineWidth = branchWidth
ctx.lineTo(endX, endY)
//sets white color for generated tree and branches
ctx.strokeStyle = 'white'
newTravel = travel
if (!newTravel) return
subBranches = mainBranch -1
/*This is where the recursion really occurs!
Each new child branch is 7/10 the size of its parent branch,
so they are generated infinitely until they "fizzle out". */
branchWidth *= .7
for (var i = 0; i < subBranches; i++) {
/*set new angles defined by a formula
that is based on the max angle multiplied by a random value.
The value can't be negative because the branches will turn in onto themselves!
newAngle = angle + rand()*maxAngle - maxAngle*.5
newLength = length * (.7 + rand()*.5)
/*uses setTimeout method with input as the drawTree function that draws tree
and its parameters. Expression is evaluated after 60 ms.
setTimeout(function () {
drawTree(ctx, endX, endY, newLength, newAngle, newTravel, branchWidth);
}, 60)
/*adds event listener that detects whether DOM has loaded, runs fractalTree regardless if content has loaded
so it triggers more quickly */
}, false);
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