Proof of concept for a triad UI component

triad-concept.js

var p = {
    x: 186,
    y: 120,
    w: 6
};

var triad = {

    first: {
        x: 292,
        y: 207
    },

    second: {
        x: 102,
        y: 205
    },

    third: {
        x: 198,
        y: 50
    }
};

var checkIfInside = function(p, p1, p2, p3) {
    //var p1 = triad.first, p2 = triad.second, p3 = triad.third;

    //Can be calculated only once:
    var denom = (p1.y - p3.y) * (p1.x - p3.x) + (p3.x - p2.x) * (p1.y - p3.y);

    //These will be continously calculated
    var pResults = {
        x: (p.x - p3.x),
        y: (p.y - p3.y)
    };

    //The rest of these can be cached if the triangle never moves
    var a = ((p2.y - p3.y) * pResults.x + (p3.x - p2.x) * pResults.y) / denom;
    var b = ((p3.y - p1.y) * pResults.x + (p1.x - p3.x) * pResults.y) / denom;
    var c = 1.0 - a - b;

    //Test whether or not a, b and c are between 0 and 1 inclusive.
    var aNormalized = (0 <= a && a <= 1);
    var bNormalized = (0 <= b && b <= 1);
    var cNormalized = (0 <= c && c <= 1);

    if(aNormalized && bNormalized && cNormalized)
    {
        return { x : a, y : b, z : c };
    }
    else
    {
        return null;
    }
};

line(triad.first.x, triad.first.y, triad.second.x, triad.second.y);
line(triad.second.x, triad.second.y, triad.third.x, triad.third.y);
line(triad.third.x, triad.third.y, triad.first.x, triad.first.y);

ellipse(p.x, p.y, p.w, p.w);

mouseDragged = function() {
    
    background(255, 255, 255);
    
    p.x = mouseX;
    p.y = mouseY;
    
    line(triad.first.x, triad.first.y, triad.second.x, triad.second.y);
    line(triad.second.x, triad.second.y, triad.third.x, triad.third.y);
    line(triad.third.x, triad.third.y, triad.first.x, triad.first.y);
    
    ellipse(p.x, p.y, p.w, p.w);

    var insideData = checkIfInside(p, triad.first, triad.second, triad.third);
    if (insideData !== null)
    {
        println("inside " + insideData.x + ", " + insideData.y + ", " + insideData.z);
    }
    else
    {
        println("outside");
    }
};