thallada.github.io/js/magic.js

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window.onload = function () {
/* Get the height and width of full document. To avoid browser
* incompatibility issues, choose the maximum of all height/width values.
*
* Method from http://stackoverflow.com/a/1147768 */
function getDocumentDimensions() {
var body = document.body,
html = document.documentElement;
var height = Math.max(body.scrollHeight, body.offsetHeight,
html.clientHeight, html.scrollHeight,
html.offsetHeight);
var width = Math.max(body.scrollWidth, body.offsetWidth,
html.clientWidth, html.scrollWidth,
html.offsetWidth);
return {"height": height, "width": width};
}
/* Specifies what will be added to the red, green, and blue values of the
* color at each interval. */
function pickGradient() {
var directions = [-1, 0, 1];
var magnitudes = [1, 2, 3];
return {"r": directions[Math.floor(Math.random() * 3)] *
magnitudes[Math.floor(Math.random() * 3)],
"g": directions[Math.floor(Math.random() * 3)] *
magnitudes[Math.floor(Math.random() * 3)],
"b": directions[Math.floor(Math.random() * 3)] *
magnitudes[Math.floor(Math.random() * 3)]};
}
/* Alters the given color by the given gradient and returns both.
If the red, green, or blue value of the color is at 0 or 255 and the
gradient for that value is not zero, then the gradient for that value
will change signs. */
function nextColor(color, gradient) {
var values = ["r", "g", "b"];
// Check if color at end of range and reverse gradient direction if so
for (var i = 0; i < 3; i++) {
var colorValue = color[values[i]];
var gradientValue = gradient[values[i]];
if ((colorValue === 255 && gradientValue > 0) ||
(colorValue === 0 && gradientValue < 0)) {
gradient[values[i]] = gradientValue * -1;
}
}
// Modify the color according to the gradient
for (i = 0; i < 3; i++) {
color[values[i]] = color[values[i]] + gradient[values[i]];
}
return {"color": color, "gradient": gradient};
}
/* Choose a random RGB color to begin the color gradient with */
function pickRandomColor() {
return {"r": Math.floor(Math.random() * (255 + 1)),
"g": Math.floor(Math.random() * (255 + 1)),
"b": Math.floor(Math.random() * (255 + 1))};
}
/* Most of this funtion is provided by Maissan Inc. in their tutorial:
http://www.maissan.net/articles/simulating-vines */
function drawTendrils(context, x, y, interations, sort, prune, prune_to) {
// Set stroke colour
context.lineWidth = 0.5;
var color = pickRandomColor();
context.strokeStyle = "rgb(" + color.r + "," + color.g + "," + color.b + ")";
// Create initial branch
var branches = [];
branches.push({
points:new Array({x:x, y:y}, {x:x, y:y}, {x:x, y:y}, {x:x, y:y}),
angle:(Math.random() * 360),
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});
// Start drawing splines at t=0
var t = 0;
// Drawing interval
var interval = setInterval(function() {
var gradient = pickGradient();
// Set stroke color
var newColor = nextColor(color, gradient);
color = newColor.color;
gradient = newColor.gradient;
context.strokeStyle = "rgb(" + color.r + "," + color.g + "," + color.b + ")";
// Draw branches
for (var i in branches) {
// Draw spline segment
var ax = (-branches[i].points[0].x + 3*branches[i].points[1].x - 3*branches[i].points[2].x + branches[i].points[3].x) / 6;
var ay = (-branches[i].points[0].y + 3*branches[i].points[1].y - 3*branches[i].points[2].y + branches[i].points[3].y) / 6;
var bx = (branches[i].points[0].x - 2*branches[i].points[1].x + branches[i].points[2].x) / 2;
var by = (branches[i].points[0].y - 2*branches[i].points[1].y + branches[i].points[2].y) / 2;
var cx = (-branches[i].points[0].x + branches[i].points[2].x) / 2;
var cy = (-branches[i].points[0].y + branches[i].points[2].y) / 2;
var dx = (branches[i].points[0].x + 4*branches[i].points[1].x + branches[i].points[2].x) / 6;
var dy = (branches[i].points[0].y + 4*branches[i].points[1].y + branches[i].points[2].y) / 6;
context.beginPath();
context.moveTo(
ax*Math.pow(t, 3) + bx*Math.pow(t, 2) + cx*t + dx,
ay*Math.pow(t, 3) + by*Math.pow(t, 2) + cy*t + dy
);
context.lineTo(
ax*Math.pow(t+0.2, 3) + bx*Math.pow(t+0.2, 2) + cx*(t+0.2) + dx,
ay*Math.pow(t+0.2, 3) + by*Math.pow(t+0.2, 2) + cy*(t+0.2) + dy
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);
context.stroke();
context.closePath();
}
// Advance t
t += 0.2;
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// When finished drawing splines, create a new set of branches
if (t >= 1) {
// Create array to store next iteration of branchces
var new_branches = [];
// Iterate over each branch
for (var j in branches) {
// Replace with 2 new branches
for (var k = 0; k < 2; k++) {
// Generate random deviation from previous angle
var angle = branches[j].angle - (Math.random() * 180 - 90);
// Generate random length
var length = Math.random() * 15 + 4;
// Calculate new point
var x2 = branches[j].points[3].x + Math.sin(Math.PI * angle / 180) * length;
var y2 = branches[j].points[3].y - Math.cos(Math.PI * angle / 180) * length;
// Add to new branch array
new_branches.push({
points:new Array(
branches[j].points[1],
branches[j].points[2],
branches[j].points[3],
{x:x2, y:y2}
),
angle:angle,
});
}
}
// If over 10 branches, prune the branches
if (prune) {
if (sort) {
while (new_branches.length > 20) new_branches.pop();
} else {
while (new_branches.length > prune_to) {
new_branches.splice(Math.floor(Math.random() * new_branches.length), 1);
}
}
}
// Replace old branch array with new
branches = new_branches;
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// Restart drawing splines at t=0
t = 0;
}
// Count interations
interations--;
if (interations < 0) clearInterval(interval);
}, 32);
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// Return interval
return interval;
}
function canvasClickHandler(event) {
var x = event.pageX;
var y = event.pageY;
var duration = Math.floor(Math.random() * (600 - 50 + 1)) + 50;
var canvas = document.getElementById("magic");
var context = canvas.getContext("2d");
var interval = drawTendrils(context, x, y, duration, false, true, 15);
}
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function draw() {
var interval_time = 2000;
var metaInterval;
function cast() {
console.log(interval_time);
clearInterval(metaInterval);
// Go slower once started
if (interval_time === 2000) {
interval_time = 4000;
} else if (interval_time > 20000) {
return; // stop drawing
} else {
interval_time = interval_time * 1.1;
}
// resize canvas if document size changed
dimensions = getDocumentDimensions();
if ((dimensions.height !== canvas.height) ||
(dimensions.width !== canvas.width)) {
canvas.height = dimensions.height;
canvas.width = dimensions.width;
}
// Find random position
var x = Math.floor(Math.random() * (canvas.width + 1));
var y = Math.floor(Math.random() * (canvas.height + 1));
var duration = Math.floor(Math.random() * (600 - 50 + 1)) + 50;
var interval = drawTendrils(context, x, y, duration, false, true, 15);
metaInterval = setInterval(cast, interval_time);
}
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// Initialize canvas
console.log("draw");
var canvas = document.getElementById("magic");
var dimensions = getDocumentDimensions();
console.log(dimensions.height);
console.log(dimensions.width);
canvas.height = dimensions.height;
canvas.width = dimensions.width;
// Check for canvas support, bind click event, and get context
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if (canvas.getContext){
canvas.addEventListener("click", canvasClickHandler);
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var context = canvas.getContext("2d");
// Cast magic spells
metaInterval = setInterval(cast, interval_time);
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}
}
draw();
};