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Filename : tracer.js
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/**
 * http://www.codeproject.com/Tips/407172/Connected-Component-Labeling-and-Vectorization
 */
var Tracer = {
    searchDirections: [[0, 1], [1, 1], [1, 0], [1, -1], [0, -1], [-1, -1], [-1, 0], [-1, 1]],
    create: function(imageWrapper, labelWrapper) {
        var imageData = imageWrapper.data,
            labelData = labelWrapper.data,
            searchDirections = this.searchDirections,
            width = imageWrapper.size.x,
            pos;

        function trace(current, color, label, edgelabel) {
            var i,
                y,
                x;

            for ( i = 0; i < 7; i++) {
                y = current.cy + searchDirections[current.dir][0];
                x = current.cx + searchDirections[current.dir][1];
                pos = y * width + x;
                if ((imageData[pos] === color) && ((labelData[pos] === 0) || (labelData[pos] === label))) {
                    labelData[pos] = label;
                    current.cy = y;
                    current.cx = x;
                    return true;
                } else {
                    if (labelData[pos] === 0) {
                        labelData[pos] = edgelabel;
                    }
                    current.dir = (current.dir + 1) % 8;
                }
            }
            return false;
        }

        function vertex2D(x, y, dir) {
            return {
                dir: dir,
                x: x,
                y: y,
                next: null,
                prev: null
            };
        }

        function contourTracing(sy, sx, label, color, edgelabel) {
            var Fv = null,
                Cv,
                P,
                ldir,
                current = {
                    cx: sx,
                    cy: sy,
                    dir: 0
                };

            if (trace(current, color, label, edgelabel)) {
                Fv = vertex2D(sx, sy, current.dir);
                Cv = Fv;
                ldir = current.dir;
                P = vertex2D(current.cx, current.cy, 0);
                P.prev = Cv;
                Cv.next = P;
                P.next = null;
                Cv = P;
                do {
                    current.dir = (current.dir + 6) % 8;
                    trace(current, color, label, edgelabel);
                    if (ldir !== current.dir) {
                        Cv.dir = current.dir;
                        P = vertex2D(current.cx, current.cy, 0);
                        P.prev = Cv;
                        Cv.next = P;
                        P.next = null;
                        Cv = P;
                    } else {
                        Cv.dir = ldir;
                        Cv.x = current.cx;
                        Cv.y = current.cy;
                    }
                    ldir = current.dir;
                } while (current.cx !== sx || current.cy !== sy);
                Fv.prev = Cv.prev;
                Cv.prev.next = Fv;
            }
            return Fv;
        }

        return {
            trace: function(current, color, label, edgelabel) {
                return trace(current, color, label, edgelabel);
            },
            contourTracing: function(sy, sx, label, color, edgelabel) {
                return contourTracing(sy, sx, label, color, edgelabel);
            }
        };
    }
};

export default (Tracer);