coreid coreid - 1 month ago 17
jQuery Question

Create external Javascript file and call it on html5 canvas

I'm using D3.js library to create example animation in simple html5 canvas.
But I won't use

<script>
inside html code. I need to create a file and put it there. So, how may I call it in Html code?

This is my html file:

<!DOCTYPE html>
<html>

<head>
<meta charset="utf-8">
<link rel="stylesheet" type="text/css" href="css/estilo.css">
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="js/delaunayanimation.js"></script>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
</head>
<body>
<section>
<canvas id="canvas">
//how to call javascript here?
</canvas>
</section>
</body>
</html>


And this is my script that I created as external (its name is delaunayanimation.js):

var width = 960,
height = 500,
τ = 2 * Math.PI,
gravity = .05;

var sample = poissonDiscSampler(width, height, 30),
nodes = [{x: 0, y: 0}],
s;

while (s = sample()) nodes.push(s);

var force = d3.layout.force()
.size([width, height])
.nodes(nodes.slice())
.gravity(0)
.charge(function(d, i) { return i ? -30 : -3000; })
.on("tick", ticked)
.start();

var voronoi = d3.geom.voronoi()
.x(function(d) { return d.x; })
.y(function(d) { return d.y; });

var root = nodes.shift();

root.fixed = true;

var links = voronoi.links(nodes);

var canvas = d3.select("#canvas").append("canvas")
.attr("width", width)
.attr("height", height)
.on("ontouchstart" in document ? "touchmove" : "mousemove", moved);

var context = canvas.node().getContext("2d");

function moved() {
var p1 = d3.mouse(this);
root.px = p1[0];
root.py = p1[1];
force.resume();
}

function ticked() {
force.resume();

for (var i = 0, n = nodes.length; i < n; ++i) {
var node = nodes[i];
node.y += (node.cy - node.y) * gravity;
node.x += (node.cx - node.x) * gravity;
}

context.clearRect(0, 0, width, height);

context.beginPath();
for (var i = 0, n = links.length; i < n; ++i) {
var link = links[i];
context.moveTo(link.source.x, link.source.y);
context.lineTo(link.target.x, link.target.y);
}
context.lineWidth = 1;
context.strokeStyle = "#bbb";
context.stroke();

context.beginPath();
for (var i = 0, n = nodes.length; i < n; ++i) {
var node = nodes[i];
context.moveTo(node.x, node.y);
context.arc(node.x, node.y, 2, 0, τ);
}
context.lineWidth = 3;
context.strokeStyle = "#fff";
context.stroke();
context.fillStyle = "#000";
context.fill();
}

// Based on https://www.jasondavies.com/poisson-disc/
function poissonDiscSampler(width, height, radius) {
var k = 30, // maximum number of samples before rejection
radius2 = radius * radius,
R = 3 * radius2,
cellSize = radius * Math.SQRT1_2,
gridWidth = Math.ceil(width / cellSize),
gridHeight = Math.ceil(height / cellSize),
grid = new Array(gridWidth * gridHeight),
queue = [],
queueSize = 0,
sampleSize = 0;

return function() {
if (!sampleSize) return sample(Math.random() * width, Math.random() * height);

// Pick a random existing sample and remove it from the queue.
while (queueSize) {
var i = Math.random() * queueSize | 0,
s = queue[i];

// Make a new candidate between [radius, 2 * radius] from the existing sample.
for (var j = 0; j < k; ++j) {
var a = 2 * Math.PI * Math.random(),
r = Math.sqrt(Math.random() * R + radius2),
x = s.x + r * Math.cos(a),
y = s.y + r * Math.sin(a);

// Reject candidates that are outside the allowed extent,
// or closer than 2 * radius to any existing sample.
if (0 <= x && x < width && 0 <= y && y < height && far(x, y)) return sample(x, y);
}

queue[i] = queue[--queueSize];
queue.length = queueSize;
}
};

function far(x, y) {
var i = x / cellSize | 0,
j = y / cellSize | 0,
i0 = Math.max(i - 2, 0),
j0 = Math.max(j - 2, 0),
i1 = Math.min(i + 3, gridWidth),
j1 = Math.min(j + 3, gridHeight);

for (j = j0; j < j1; ++j) {
var o = j * gridWidth;
for (i = i0; i < i1; ++i) {
if (s = grid[o + i]) {
var s,
dx = s.x - x,
dy = s.y - y;
if (dx * dx + dy * dy < radius2) return false;
}
}
}

return true;
}

function sample(x, y) {
var s = {x: x, y: y, cx: x, cy: y};
queue.push(s);
grid[gridWidth * (y / cellSize | 0) + (x / cellSize | 0)] = s;
++sampleSize;
++queueSize;
return s;
}
}

Answer

Your problem is that you're trying to append a <canvas> inside a <canvas>, which is pointless. This line:

var canvas = d3.select("#canvas").append("canvas")

looks for an element with ID "canvas" and append a <canvas> inside it. But in your HTML, that element is a canvas:

<section>
    <canvas id="canvas">
    </canvas>
</section>

If you just change this to a <div>, for instance:

<section>
    <div id="canvas">
    </div>
</section>

your code will work. Here is a working fiddle to show you (the only thing I did was the above mentioned change): https://jsfiddle.net/vcg1pk9v/1/

Also, have Spencer's answer in mind: the code that manipulates that div has to come after that div is created (in JSFiddle, the code will run after automatically). A good practice is putting it (or calling it, if external) just before closing the <body>. That being said, your question has actually two problems; Spencer dealt with one of them, I dealt with the other.

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