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<html>
<head>
<title>Angular Gradient Test</title>
<script type="text/javascript" src="graphics.js"></script>
<script type="text/javascript" src="math.js"></script>
<script type="text/javascript">
function draw() {
var canvas = document.getElementById("canvas");
var halfWidth = canvas.width / 2;
var halfHeight = canvas.height / 2;
var gradientCenter = new Point(halfWidth, halfHeight);
var colors = [ [1, 0, 0, 1], // red
[0, 1, 0, 1], // green
[0, 0, 1, 1] // blue
];
var angularGradient = function(point) {
// figure out angle
var dir = point.sub(gradientCenter);
var angle = Math.atan2(dir.y, dir.x);
// wrap around as positive
if (dir.y < 0 ) {
angle += 2 * Math.PI;
}
// map to [0, 1] range
angle /= (2 * Math.PI);
// figure out which segments to interpolate
var angleRatio = angle * colors.length;
var index = Math.floor(angleRatio);
var leftColor = index == 0? colors[colors.length - 1]:
colors[index - 1];
var rightColor = colors[index];
// figure out interpolation factor
var lerpFac = angleRatio % 1;
return lerp(leftColor, rightColor, lerpFac);
}
process(canvas, angularGradient);
}
</script>
</head>
<body onload="draw()">
<canvas id="canvas" width="300" height="300"></canvas>
</body>
</html>
function process(canvas, func) {
function setPixel(imageData, x, y, rgba) {
var index = (x + y * imageData.width) * 4;
for (var i = 0; i < 4; i++) {
imageData.data[index + i] = rgba[i] * 255;
}
}
var ctx = canvas.getContext("2d");
var imageData = ctx.createImageData(canvas.width,
canvas.height);
for (var y = 0; y < canvas.height; y++) {
for (var x = 0; x < canvas.width; x++) {
var result = func(new Point(x, y));
setPixel(imageData, x, y, result);
}
}
ctx.putImageData(imageData, 0, 0);
}
function lerp(a, b, fac) {
var ret = [];
if(a == b) {
return a;
}
for (var i = 0; i < Math.min(a.length, b.length); i++) {
ret[i] = a[i] * (1 - fac) + b[i] * fac;
}
return ret;
}
function project(target, initial, current) {
var delta = initial.sub(target);
if( (delta.x == 0) && (delta.y == 0) ) {
return target;
}
var t = current.sub(target).mul(delta).div(delta.toDistSquared());
return delta.mul(t.x + t.y).add(target);
}
function dot(a, b) {
return a.x * b.x + a.y * b.y;
}
function Circle(location, radius) {
this.init(location, radius);
}
Circle.prototype = {
init: function(location, radius) {
this.location = location? new Point(location[0], location[1]): new Point();
this.radius = radius? radius: 1;
},
contains: function(p) {
return p.sub(this.location).toDist() <= this.radius;
},
intersect: function(p1, p2) {
// http://local.wasp.uwa.edu.au/~pbourke/geometry/sphereline/
var dp = p2.sub(p1);
var a = dp.toDistSquared();
var b = 2 * (dp.x * (p1.x - this.location.x) +
dp.y * (p1.y - this.location.y));
var c = this.location.toDistSquared() + p1.toDistSquared() - 2 *
(this.location.x * p1.x + this.location.y * p1.y) -
this.radius * this.radius;
var bb4ac = b * b - 4 * a * c;
var epsilon = 0.0001;
if (Math.abs(a) < epsilon || bb4ac < 0) {
return [];
}
if (bb4ac == 0) {
return [p2.sub(p1).mul(-b / (2 * a)).add(p1)];
}
var mu1 = (-b + Math.sqrt(bb4ac)) / (2 * a);
var mu2 = (-b - Math.sqrt(bb4ac)) / (2 * a);
return [p2.sub(p1).mul(mu1).add(p1), p2.sub(p1).mul(mu2).add(p1)]
}
}
function Point(x, y) {
this.init(x, y);
}
Point.prototype = {
init: function(x, y) {
this.x = x? x: 0;
this.y = y? y: 0;
},
add: function(other) {
return this._operationTemplate(other, function(a, b) {return a + b});
},
sub: function(other) {
return this._operationTemplate(other, function(a, b) {return a - b});
},
mul: function(other) {
return this._operationTemplate(other, function(a, b) {return a * b});
},
div: function(other) {
return this._operationTemplate(other, function(a, b) {return a / b});
},
ceil: function() {
return this._operationTemplate(null, function(a) {return Math.ceil(a)});
},
floor: function() {
return this._operationTemplate(null, function(a) {return Math.floor(a)});
},
round: function() {
return this._operationTemplate(null, function(a) {return Math.round(a)});
},
_operationTemplate: function(other, op) {
if(isNumber(other)) {
return new Point(op(this.x, other), op(this.y, other));
}
if(other == null) {
return new Point(op(this.x), op(this.y));
}
return new Point(op(this.x, other.x), op(this.y, other.y));
},
toDist: function() {
return Math.sqrt(this.toDistSquared());
},
toDistSquared: function() {
return this.x * this.x + this.y * this.y;
},
normalize: function() {
return this.div(this.toDist());
},
invert: function() {
return new Point(-this.x, -this.y);
},
closest: function(points) {
return this._findTemplate(points,
function() {
return Number.MAX_VALUE;
},
function(dist, recordDist) {
return dist < recordDist;
}
);
},
farthest: function(points) {
return this._findTemplate(points,
function() {
return 0;
},
function(dist, recordDist) {
return dist > recordDist;
}
);
},
_findTemplate: function(points, init, compare) {
var record = init();
var recordPoint = points[0];
for (var i = 1; i < points.length; i++) {
var point = points[i];
var dist = this.sub(point).toDist();
if (compare(dist, record)) {
record = dist;
recordPoint = point;
}
}
return recordPoint;
}
}
function isNumber(n) {
return !isNaN(parseFloat(n)) && isFinite(n);
}
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