source code: qh.js

function getRandomPoints(numPoint, xMax, yMax) {
    var points = new Array();
    var phase = Math.random() * Math.PI * 2;
    for (var i = 0; i < numPoint/2; i++) {
        var r =  Math.random()*xMax/4;
        var theta = Math.random() * 1.5 * Math.PI + phase;
        points.push( [ xMax /4 + r * Math.cos(theta), yMax/2 + 2 * r * Math.sin(theta) ] )
    }
    var phase = Math.random() * Math.PI * 2;
    for (var i = 0; i < numPoint/2; i++) {
        var r =  Math.random()*xMax/4;
        var theta = Math.random() * 1.5 * Math.PI + phase;
        points.push( [ xMax /4 * 3 +  r * Math.cos(theta), yMax/2 +  r * Math.sin(theta) ] )
    }
    return points
}

function getDistant(cpt, bl) {
    Vy = bl[1][0] - bl[0][0];
    Vx = bl[0][1] - bl[1][1];
    return (Vx * (cpt[0] - bl[0][0]) + Vy * (cpt[1] -bl[0][1]))
}

function findMostDistantPointFromBaseLine(baseLine, points) {
    var maxD = 0;
    var maxPt = new Array();
    var newPoints = new Array();
    for (var idx in points) {
        var pt = points[idx];
        var d = getDistant(pt, baseLine);

        if ( d > 0) {
            newPoints.push(pt);
        } else {
            continue;
        }

        if ( d > maxD ) {
            maxD = d;
            maxPt = pt;
        }

    }
    return {'maxPoint':maxPt, 'newPoints':newPoints}
}

var allBaseLines = new Array();
function buildConvexHull(baseLine, points) {

    //plotBaseLine(baseLine,'rgb(180,180,180)');
    allBaseLines.push(baseLine)
    var convexHullBaseLines = new Array();
    var t = findMostDistantPointFromBaseLine(baseLine, points);
    if (t.maxPoint.length) {
        convexHullBaseLines = convexHullBaseLines.concat( buildConvexHull( [baseLine[0],t.maxPoint], t.newPoints) );
        convexHullBaseLines = convexHullBaseLines.concat( buildConvexHull( [t.maxPoint,baseLine[1]], t.newPoints) );
        return convexHullBaseLines;
    } else {
        return [baseLine];
    }
}

function getConvexHull(points) {
    //find first baseline
    var maxX, minX;
    var maxPt, minPt;
    for (var idx in points) {
        var pt = points[idx];
        if (pt[0] > maxX || !maxX) {
            maxPt = pt;
            maxX = pt[0];
        }
        if (pt[0] < minX || !minX) {
            minPt = pt;
            minX = pt[0];
        }
    }
    var ch = [].concat(buildConvexHull([minPt, maxPt], points),
                       buildConvexHull([maxPt, minPt], points))
    return ch;
}

function plotBaseLine(baseLine,color) {
    var ctx = document.getElementById('qh_demo').getContext('2d');
    var pt1 = baseLine[0]
    var pt2 = baseLine[1];
    ctx.save()
    ctx.strokeStyle = color;
    ctx.beginPath();
    ctx.moveTo(pt1[0],pt1[1]);
    ctx.lineTo(pt2[0],pt2[1]);
    ctx.stroke();
    ctx.restore();
}

var pts;

function qhPlotPoints() {
    ctx = document.getElementById('qh_demo').getContext('2d');
    ctx.clearRect(0,0,200,200);
    ctx.fillStyle = 'rgb(0,0,0)';
    pts = getRandomPoints(250,200,200);
    for (var idx in pts) {
        var pt = pts[idx];
        ctx.fillRect(pt[0],pt[1],2,2);
    }
}

function qhPlotConvexHull() {
    var ch = getConvexHull(pts);
    var eBL = allBaseLines[0];
    function plotIntermediateBL() {
        var l = allBaseLines.shift();
        if (l) {
            plotBaseLine(l, 'rgb(180,180,180)');
            setTimeout(plotIntermediateBL, 250);
        } else {
            for (var idx in ch) {
                var baseLine = ch[idx];
                plotBaseLine(baseLine, 'rgb(255,0,0)');
            }
            plotBaseLine(eBL,'rgb(0,255,0)');
        }
    }
    plotIntermediateBL();
}


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