A small library of vector math functions used by some of my Roll20 scripts

VectorMath.js

/** Returns an array representing a 2D vector from pt1 to pt2. */
var vec = function(pt1, pt2) {
    return [pt2[0]-pt1[0], pt2[1]-pt1[1]];
}


/** Returns the length of an array representing a vector. */
var vecLength = function(vector) {
    var length = 0;
    for(var i=0; i < vector.length; i++) {
        length += vector[i]*vector[i];
    }
    return Math.sqrt(length);
}


/** Returns an array representing the cross product of two 3D vectors. */
var vecCrossProduct = function(v1, v2) {
    var x = v1[1]*v2[2] - v1[2]*v2[1];
    var y = v1[2]*v2[0] - v1[0]*v2[2];
    var z = v1[0]*v2[1] - v1[1]*v2[0];
    return [x, y, z];
}


/** Returns the cross product of two vectors. */
var vecDotProduct = function(v1, v2) {
    var result = 0;
    for(var i = 0; i < v1.length; i++) {
        result += v1[i]*v2[i];
    }
    return result;
}


/** Computes the distance from a point to an infinitely stretching line. */
var ptLineDist = function(pt, linePt1, linePt2) {
    var a = vec(linePt1, linePt2);
    var b = vec(linePt1, pt);
    
    var lenA = vecLength(a);
    var lenAxB = vecLength(vecCrossProduct(a, b));
    
    if(lenA == 0) {
        return NaN;
    }
    else {
        return lenAxB/lenA;
    }
}


/** Computes the distance from a point to a line segment. */
var ptSegDist = function(pt, linePt1, linePt2) {
    var a = vec(linePt1, linePt2);
    var b = vec(linePt1, pt);
    a[2] = 0;
    b[2] = 0;
    
//    log(a);
//    log(b);
    
    var aDotb = vecDotProduct(a,b);
//    log("aDotb = " + aDotb);
    
    // Is pt behind linePt1?
    if(aDotb < 0) {
    //    log("pt before");
        return vecLength(vec(pt, linePt1));
    }
    
    // Is pt after linePt2?
    else if(aDotb > vecDotProduct(a,a)) {
    //    log("pt after");
        return vecLength(vec(pt, linePt2));
    }
    
    // Pt must be between linePt1 and linePt2.
    else {
    //    log("pt between");
        var lenA = vecLength(a);
        var AxB = vecCrossProduct(a,b);
        var lenAxB = vecLength(AxB);
        
    //    log("lenA = " + lenA);
    //    log("AxB = " + AxB);
    //    log("lenAxB = " + lenAxB);
        
        return Math.abs(lenAxB/lenA);
    }
}