281 lines
10 KiB
JavaScript
281 lines
10 KiB
JavaScript
window.onload = function () {
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// Array to hold all active spells being drawn
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var spells = [];
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// When on, wait a certain amount of time before casting (for initial
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// load-up)
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var counting = true;
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// How fast to draw the spells
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var step = 0.2;
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// Limit of branches per spell at any time
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var prune_to = 20;
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// Save this query here now that the page is loaded
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var canvas = document.getElementById("magic");
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/* Get the height and width of full document. To avoid browser
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* incompatibility issues, choose the maximum of all height/width values.
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*
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* Method from http://stackoverflow.com/a/1147768 */
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function getDocumentDimensions() {
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var body = document.body,
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html = document.documentElement;
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var height = Math.max(body.scrollHeight, body.offsetHeight,
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html.clientHeight, html.scrollHeight,
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html.offsetHeight);
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var width = Math.max(body.scrollWidth, body.offsetWidth,
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html.clientWidth, html.scrollWidth,
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html.offsetWidth);
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return {"height": height, "width": width};
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}
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/* Specifies what will be added to the red, green, and blue values of the
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* color at each interval. */
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function pickGradient() {
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var directions = [-1, 0, 1];
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var magnitudes = [1, 2, 3];
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return {"r": directions[Math.floor(Math.random() * 3)] *
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magnitudes[Math.floor(Math.random() * 3)],
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"g": directions[Math.floor(Math.random() * 3)] *
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magnitudes[Math.floor(Math.random() * 3)],
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"b": directions[Math.floor(Math.random() * 3)] *
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magnitudes[Math.floor(Math.random() * 3)]};
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}
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/* Alters the given color by the given gradient and returns both.
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If the red, green, or blue value of the color is at 0 or 255 and the
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gradient for that value is not zero, then the gradient for that value
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will change signs.
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Unused for now. It turns out that changing the canvas stroke color is a
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costly operation and slows things down a lot. */
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function nextColor(color, gradient) {
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var values = ["r", "g", "b"];
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// Check if color at end of range and reverse gradient direction if so
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for (var i = 0; i < 3; i++) {
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var colorValue = color[values[i]];
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var gradientValue = gradient[values[i]];
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if ((colorValue === 255 && gradientValue > 0) ||
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(colorValue === 0 && gradientValue < 0)) {
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gradient[values[i]] = gradientValue * -1;
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}
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}
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// Modify the color according to the gradient
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for (i = 0; i < 3; i++) {
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color[values[i]] = color[values[i]] + gradient[values[i]];
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}
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return {"color": color, "gradient": gradient};
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}
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/* Choose a random RGB color to begin the color gradient with */
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function pickRandomColor() {
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return {"r": Math.floor(Math.random() * (255 + 1)),
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"g": Math.floor(Math.random() * (255 + 1)),
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"b": Math.floor(Math.random() * (255 + 1))};
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}
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function drawSplineSegment(branch, context) {
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var ax = (-branch.points[0].x + 3*branch.points[1].x - 3*branch.points[2].x + branch.points[3].x) / 6;
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var ay = (-branch.points[0].y + 3*branch.points[1].y - 3*branch.points[2].y + branch.points[3].y) / 6;
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var bx = (branch.points[0].x - 2*branch.points[1].x + branch.points[2].x) / 2;
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var by = (branch.points[0].y - 2*branch.points[1].y + branch.points[2].y) / 2;
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var cx = (-branch.points[0].x + branch.points[2].x) / 2;
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var cy = (-branch.points[0].y + branch.points[2].y) / 2;
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var dx = (branch.points[0].x + 4*branch.points[1].x + branch.points[2].x) / 6;
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var dy = (branch.points[0].y + 4*branch.points[1].y + branch.points[2].y) / 6;
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context.moveTo(
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ax*Math.pow(branch.t, 3) + bx*Math.pow(branch.t, 2) + cx*branch.t + dx,
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ay*Math.pow(branch.t, 3) + by*Math.pow(branch.t, 2) + cy*branch.t + dy
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);
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context.lineTo(
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ax*Math.pow(branch.t+step, 3) + bx*Math.pow(branch.t+step, 2) + cx*(branch.t+step) + dx,
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ay*Math.pow(branch.t+step, 3) + by*Math.pow(branch.t+step, 2) + cy*(branch.t+step) + dy
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);
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branch.t += step;
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}
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function splitBranch(branch) {
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var newBranches = [];
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// Replace with 2 new branches
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for (var k = 0; k < 2; k++) {
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// Generate random deviation from previous angle
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var angle = branch.angle - (Math.random() * 180 - 90);
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// Generate random length
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var length = Math.random() * 15 + 4;
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// Calculate new point
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var x2 = branch.points[3].x + Math.sin(Math.PI * angle / 180) * length;
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var y2 = branch.points[3].y - Math.cos(Math.PI * angle / 180) * length;
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// Add to new branch array
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newBranches.push({
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points:new Array(
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branch.points[1],
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branch.points[2],
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branch.points[3],
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{x:x2, y:y2}
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),
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angle:angle,
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t:0,
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});
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}
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return newBranches;
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}
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function cast(x, y, angle, chain) {
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// Find random position if not defined
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if (x === undefined) {
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x = Math.floor(Math.random() * (canvas.width + 1));
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}
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if (y === undefined) {
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y = Math.floor(Math.random() * (canvas.height + 1));
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}
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if (angle === undefined) {
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angle = Math.random() * 360;
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}
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var color = pickRandomColor();
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var colorString = "rgb(" + color.r + "," + color.g + "," + color.b + ")";
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// Create new spell (branch)
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spells.push({
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branches:new Array({
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points:new Array({x:x, y:y}, {x:x, y:y}, {x:x, y:y}, {x:x, y:y}),
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angle:angle,
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t:0,
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}),
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color:colorString,
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duration:Math.floor(Math.random() * (600 - 50 + 1)) + 50,
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chain:chain,
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});
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}
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/* Most of this funtion is provided by Maissan Inc. in their tutorial:
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http://www.maissan.net/articles/simulating-vines */
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function drawSpells(context, sort, prune, chain) {
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var AnimationFrame = window.AnimationFrame;
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AnimationFrame.shim();
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var animationFrame = new AnimationFrame(30),
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timeCounter = 0,
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waitTime = 50,
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color,
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gradient;
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context.lineWidth = 0.5;
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function animate(time) {
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// resize canvas if document size changed
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dimensions = getDocumentDimensions();
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if ((dimensions.height !== canvas.height) ||
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(dimensions.width !== canvas.width)) {
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canvas.height = dimensions.height;
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canvas.width = dimensions.width;
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}
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// if enough time has passed, cast another spell to draw
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if (timeCounter >= waitTime && counting) {
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cast(5, 5, 270, chain); // start position
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counting = false;
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}
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// Draw branches
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for (var i in spells) {
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context.beginPath();
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context.strokeStyle = spells[i].color;
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if (spells[i].duration > 0) {
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for (var j in spells[i].branches) {
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drawSplineSegment(spells[i].branches[j], context);
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// When finished drawing splines, create a new set of branches
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if (spells[i].branches[j].t >= 1) {
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var newBranches = splitBranch(spells[i].branches[j]);
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// Replace old branch with two new branches
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spells[i].branches.splice(j, 1);
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spells[i].branches = spells[i].branches.concat(newBranches);
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}
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}
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// If over 10 branches, prune the branches
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if (prune) {
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if (sort) {
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while (spells[i].branches.length > prune_to) {
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spells[i].branches.pop();
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}
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} else {
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while (spells[i].branches.length > prune_to) {
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spells[i].branches.splice(
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Math.floor(Math.random() * spells[i].branches.length),
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1);
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}
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}
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}
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context.stroke();
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context.closePath();
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spells[i].duration--;
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} else {
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// cast a new spell at random position
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if (spells[i].chain) {
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cast(undefined, undefined, undefined, true);
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}
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spells.splice(i, 1); // spell is done now
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}
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}
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if (counting) {
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timeCounter++;
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}
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frameId = animationFrame.request(animate);
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}
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// Drawing interval
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var frameId = animationFrame.request(animate);
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return frameId;
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}
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function canvasClickHandler(event) {
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var x = event.pageX;
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var y = event.pageY;
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cast(x, y, undefined, false);
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}
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function draw() {
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var interval_time = 2000;
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// Initialize canvas
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var dimensions = getDocumentDimensions();
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canvas.height = dimensions.height;
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canvas.width = dimensions.width;
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// Check for canvas support, bind click event, and get context
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if (canvas.getContext){
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canvas.addEventListener("click", canvasClickHandler);
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var context = canvas.getContext("2d");
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// Cast magic spells
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var frameId = drawSpells(context, false, true, true);
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}
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}
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draw();
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};
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