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@bebraw
Created Jul 30, 2010
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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 = [];
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);
}
<html>
<head>
<title>Radial 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(x, y) {
var canvas = document.getElementById("canvas");
var halfWidth = canvas.width / 2;
var halfHeight = canvas.height / 2;
var gradientCenterX = x != undefined? x: halfWidth;
var gradientCenterY = y != undefined? y: halfHeight;
var outerCircle = new Circle([halfWidth, halfHeight],
halfWidth);
outerCircle.color = [0.5, 0.5, 1, 0.5]; // semi-opaque light blue
var innerCircle = new Circle([gradientCenterX,
gradientCenterY], 5);
innerCircle.color = [0, 0, 0.2, 1]; // opaque dark blue
var radialGradient = function(point) {
var lerpFac = 1;
if (!outerCircle.contains(point)) {
lerpFac = 1;
}
else if (innerCircle.contains(point)) {
lerpFac = 0;
}
else {
var outerIntersections = outerCircle.intersect(point,
innerCircle.location);
var innerIntersections = innerCircle.intersect(point,
innerCircle.location);
var closestInner = point.closest(innerIntersections);
var farthestOuter = closestInner.farthest(outerIntersections);
var innerOuterDist = closestInner.sub(farthestOuter).
toDist();
var innerPointDist = closestInner.sub(point).toDist();
lerpFac = innerPointDist / innerOuterDist;
}
return lerp(innerCircle.color, outerCircle.color, lerpFac);
}
process(canvas, radialGradient);
}
function move(event) {
draw(event.x - event.srcElement.offsetLeft,
event.y - event.srcElement.offsetTop);
}
</script>
</head>
<body onload="draw()">
<canvas onmousemove="move(event)" id="canvas" width="100" height="100"></canvas>
</body>
</html>
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