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Edit File: bbox.js

// The Bounding Box object

function derive(v0, v1, v2, v3, t) {
    return Math.pow(1 - t, 3) * v0 +
        3 * Math.pow(1 - t, 2) * t * v1 +
        3 * (1 - t) * Math.pow(t, 2) * v2 +
        Math.pow(t, 3) * v3;
}
/**
 * A bounding box is an enclosing box that describes the smallest measure within which all the points lie.
 * It is used to calculate the bounding box of a glyph or text path.
 *
 * On initialization, x1/y1/x2/y2 will be NaN. Check if the bounding box is empty using `isEmpty()`.
 *
 * @exports opentype.BoundingBox
 * @class
 * @constructor
 */
function BoundingBox() {
    this.x1 = Number.NaN;
    this.y1 = Number.NaN;
    this.x2 = Number.NaN;
    this.y2 = Number.NaN;
}

/**
 * Returns true if the bounding box is empty, that is, no points have been added to the box yet.
 */
BoundingBox.prototype.isEmpty = function() {
    return isNaN(this.x1) || isNaN(this.y1) || isNaN(this.x2) || isNaN(this.y2);
};

/**
 * Add the point to the bounding box.
 * The x1/y1/x2/y2 coordinates of the bounding box will now encompass the given point.
 * @param {number} x - The X coordinate of the point.
 * @param {number} y - The Y coordinate of the point.
 */
BoundingBox.prototype.addPoint = function(x, y) {
    if (typeof x === 'number') {
        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 (typeof y === 'number') {
        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;
        }
    }
};

/**
 * Add a X coordinate to the bounding box.
 * This extends the bounding box to include the X coordinate.
 * This function is used internally inside of addBezier.
 * @param {number} x - The X coordinate of the point.
 */
BoundingBox.prototype.addX = function(x) {
    this.addPoint(x, null);
};

/**
 * Add a Y coordinate to the bounding box.
 * This extends the bounding box to include the Y coordinate.
 * This function is used internally inside of addBezier.
 * @param {number} y - The Y coordinate of the point.
 */
BoundingBox.prototype.addY = function(y) {
    this.addPoint(null, y);
};

/**
 * Add a Bézier curve to the bounding box.
 * This extends the bounding box to include the entire Bézier.
 * @param {number} x0 - The starting X coordinate.
 * @param {number} y0 - The starting Y coordinate.
 * @param {number} x1 - The X coordinate of the first control point.
 * @param {number} y1 - The Y coordinate of the first control point.
 * @param {number} x2 - The X coordinate of the second control point.
 * @param {number} y2 - The Y coordinate of the second control point.
 * @param {number} x - The ending X coordinate.
 * @param {number} y - The ending Y coordinate.
 */
BoundingBox.prototype.addBezier = function(x0, y0, x1, y1, x2, y2, x, y) {
    // This code is based on http://nishiohirokazu.blogspot.com/2009/06/how-to-calculate-bezier-curves-bounding.html
    // and https://github.com/icons8/svg-path-bounding-box

const p0 = [x0, y0];
    const p1 = [x1, y1];
    const p2 = [x2, y2];
    const p3 = [x, y];

this.addPoint(x0, y0);
    this.addPoint(x, y);

for (let i = 0; i <= 1; i++) {
        const b = 6 * p0[i] - 12 * p1[i] + 6 * p2[i];
        const a = -3 * p0[i] + 9 * p1[i] - 9 * p2[i] + 3 * p3[i];
        const c = 3 * p1[i] - 3 * p0[i];

if (a === 0) {
            if (b === 0) continue;
            const t = -c / b;
            if (0 < t && t < 1) {
                if (i === 0) this.addX(derive(p0[i], p1[i], p2[i], p3[i], t));
                if (i === 1) this.addY(derive(p0[i], p1[i], p2[i], p3[i], t));
            }
            continue;
        }

const b2ac = Math.pow(b, 2) - 4 * c * a;
        if (b2ac < 0) continue;
        const t1 = (-b + Math.sqrt(b2ac)) / (2 * a);
        if (0 < t1 && t1 < 1) {
            if (i === 0) this.addX(derive(p0[i], p1[i], p2[i], p3[i], t1));
            if (i === 1) this.addY(derive(p0[i], p1[i], p2[i], p3[i], t1));
        }
        const t2 = (-b - Math.sqrt(b2ac)) / (2 * a);
        if (0 < t2 && t2 < 1) {
            if (i === 0) this.addX(derive(p0[i], p1[i], p2[i], p3[i], t2));
            if (i === 1) this.addY(derive(p0[i], p1[i], p2[i], p3[i], t2));
        }
    }
};

/**
 * Add a quadratic curve to the bounding box.
 * This extends the bounding box to include the entire quadratic curve.
 * @param {number} x0 - The starting X coordinate.
 * @param {number} y0 - The starting Y coordinate.
 * @param {number} x1 - The X coordinate of the control point.
 * @param {number} y1 - The Y coordinate of the control point.
 * @param {number} x - The ending X coordinate.
 * @param {number} y - The ending Y coordinate.
 */
BoundingBox.prototype.addQuad = function(x0, y0, x1, y1, x, y) {
    const cp1x = x0 + 2 / 3 * (x1 - x0);
    const cp1y = y0 + 2 / 3 * (y1 - y0);
    const cp2x = cp1x + 1 / 3 * (x - x0);
    const cp2y = cp1y + 1 / 3 * (y - y0);
    this.addBezier(x0, y0, cp1x, cp1y, cp2x, cp2y, x, y);
};

export default BoundingBox;