react-native-svg/lib/BoundingBox.js

// from https://github.com/gabelerner/canvg/blob/860e418aca67b9a41e858a223d74d375793ec364/canvg.js#L449

class BoundingBox{
    constructor(x1, y1, x2, y2) {
        this.x1 = NaN;
        this.y1 = NaN;
        this.x2 = NaN;
        this.y2 = NaN;

        this.addPoint(x1, y1);
        this.addPoint(x2, y2);
    }

    width = () => this.x2 - this.x1;

    height = () => this.y2 - this.y1;

    addPoint = (x, y) => {
        if (x != null) {
            if (isNaN(this.x1) || isNaN(this.x2)) {
                this.x1 = x;
                this.x2 = x;
            }
            if (x < this.x1) this.x1 = x;
            if (x > this.x2) this.x2 = x;
        }

        if (y != null) {
            if (isNaN(this.y1) || isNaN(this.y2)) {
                this.y1 = y;
                this.y2 = y;
            }
            if (y < this.y1) this.y1 = y;
            if (y > this.y2) this.y2 = y;
        }
    };

    addX = x => this.addPoint(x, null);

    addY = y => this.addPoint(null, y);

    addQuadraticCurve = (p0x, p0y, p1x, p1y, p2x, p2y) => {
        let cp1x = p0x + 2 / 3 * (p1x - p0x); // CP1 = QP0 + 2/3 *(QP1-QP0)
        let cp1y = p0y + 2 / 3 * (p1y - p0y); // CP1 = QP0 + 2/3 *(QP1-QP0)
        let cp2x = cp1x + 1 / 3 * (p2x - p0x); // CP2 = CP1 + 1/3 *(QP2-QP0)
        let cp2y = cp1y + 1 / 3 * (p2y - p0y); // CP2 = CP1 + 1/3 *(QP2-QP0)
        this.addBezierCurve(p0x, p0y, cp1x, cp2x, cp1y, cp2y, p2x, p2y);
    };

    addBezierCurve = (p0x, p0y, p1x, p1y, p2x, p2y, p3x, p3y) => {
        // from http://blog.hackers-cafe.net/2009/06/how-to-calculate-bezier-curves-bounding.html
        var p0 = [p0x, p0y],
            p1 = [p1x, p1y],
            p2 = [p2x, p2y],
            p3 = [p3x, p3y];

        this.addPoint(p0[0], p0[1]);
        this.addPoint(p3[0], p3[1]);

        [0, 1].forEach(i => {
            let f = t => {
                return Math.pow(1 - t, 3) * p0[i]
                    + 3 * Math.pow(1 - t, 2) * t * p1[i]
                    + 3 * (1 - t) * Math.pow(t, 2) * p2[i]
                    + Math.pow(t, 3) * p3[i];
            };

            let b = 6 * p0[i] - 12 * p1[i] + 6 * p2[i];
            let a = -3 * p0[i] + 9 * p1[i] - 9 * p2[i] + 3 * p3[i];
            let c = 3 * p1[i] - 3 * p0[i];

            if (a == 0) {
                if (b != 0) {
                    let t = -c / b;
                    if (0 < t && t < 1) {
                        if (i == 0) this.addX(f(t));
                        if (i == 1) this.addY(f(t));
                    }
                }
                return;
            }

            let b2ac = Math.pow(b, 2) - 4 * c * a;
            if (b2ac < 0) {
                return;
            }
            let t1 = (-b + Math.sqrt(b2ac)) / (2 * a);
            if (0 < t1 && t1 < 1) {
                i == 0 && this.addX(f(t1));
                i == 1 && this.addY(f(t1));
            }
            let t2 = (-b - Math.sqrt(b2ac)) / (2 * a);
            if (0 < t2 && t2 < 1) {
                i == 0 && this.addX(f(t2));
                i == 1 && this.addY(f(t2));
            }
        });
    };
}

export default BoundingBox;