blob: 71533cb63237d9f786a901e0e657b6af3dc6860e [file] [log] [blame]
/*
Geometry library - based on work by Mike Bostock.
*/
(function() {
if (typeof geo == 'undefined') {
geo = {};
}
var tolerance = 1e-10;
function eq(a, b) {
return (Math.abs(a - b) < tolerance);
}
function gt(a, b) {
return (a - b > -tolerance);
}
function lt(a, b) {
return gt(b, a);
}
geo.eq = eq;
geo.gt = gt;
geo.lt = lt;
geo.LineSegment = function(x1, y1, x2, y2) {
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
// Ax + By = C
this.a = y2 - y1;
this.b = x1 - x2;
this.c = x1 * this.a + y1 * this.b;
if (eq(this.a, 0) && eq(this.b, 0)) {
throw new Error(
'Cannot construct a LineSegment with two equal endpoints.');
}
};
geo.LineSegment.prototype.intersect = function(that) {
var d = (this.x1 - this.x2) * (that.y1 - that.y2) -
(this.y1 - this.y2) * (that.x1 - that.x2);
if (eq(d, 0)) {
// The two lines are parallel or very close.
return {
x : NaN,
y : NaN
};
}
var t1 = this.x1 * this.y2 - this.y1 * this.x2,
t2 = that.x1 * that.y2 - that.y1 * that.x2,
x = (t1 * (that.x1 - that.x2) - t2 * (this.x1 - this.x2)) / d,
y = (t1 * (that.y1 - that.y2) - t2 * (this.y1 - this.y2)) / d,
in1 = (gt(x, Math.min(this.x1, this.x2)) && lt(x, Math.max(this.x1, this.x2)) &&
gt(y, Math.min(this.y1, this.y2)) && lt(y, Math.max(this.y1, this.y2))),
in2 = (gt(x, Math.min(that.x1, that.x2)) && lt(x, Math.max(that.x1, that.x2)) &&
gt(y, Math.min(that.y1, that.y2)) && lt(y, Math.max(that.y1, that.y2)));
return {
x : x,
y : y,
in1 : in1,
in2 : in2
};
};
geo.LineSegment.prototype.x = function(y) {
// x = (C - By) / a;
if (this.a) {
return (this.c - this.b * y) / this.a;
} else {
// a == 0 -> horizontal line
return NaN;
}
};
geo.LineSegment.prototype.y = function(x) {
// y = (C - Ax) / b;
if (this.b) {
return (this.c - this.a * x) / this.b;
} else {
// b == 0 -> vertical line
return NaN;
}
};
geo.LineSegment.prototype.length = function() {
return Math.sqrt(
(this.y2 - this.y1) * (this.y2 - this.y1) +
(this.x2 - this.x1) * (this.x2 - this.x1));
};
geo.LineSegment.prototype.offset = function(x, y) {
return new geo.LineSegment(
this.x1 + x, this.y1 + y,
this.x2 + x, this.y2 + y);
};
})();