Function projectPointToArc

src/label/labelGuideHelper.ts:86–151

(
    cx: number, cy: number, r: number, startAngle: number, endAngle: number, anticlockwise: boolean,
    x: number, y: number, out: number[]
)

function projectPointToArc(
    cx: number, cy: number, r: number, startAngle: number, endAngle: number, anticlockwise: boolean,
    x: number, y: number, out: number[]
): number {
    x -= cx;
    y -= cy;
    const d = Math.sqrt(x * x + y * y);
    x /= d;
    y /= d;

    // Intersect point.
    const ox = x * r + cx;
    const oy = y * r + cy;

    if (Math.abs(startAngle - endAngle) % PI2 < 1e-4) {
        // Is a circle
        out[0] = ox;
        out[1] = oy;
        return d - r;
    }

    if (anticlockwise) {
        const tmp = startAngle;
        startAngle = normalizeRadian(endAngle);
        endAngle = normalizeRadian(tmp);
    }
    else {
        startAngle = normalizeRadian(startAngle);
        endAngle = normalizeRadian(endAngle);
    }
    if (startAngle > endAngle) {
        endAngle += PI2;
    }

    let angle = Math.atan2(y, x);
    if (angle < 0) {
        angle += PI2;
    }
    if ((angle >= startAngle && angle <= endAngle)
        || (angle + PI2 >= startAngle && angle + PI2 <= endAngle)) {
        // Project point is on the arc.
        out[0] = ox;
        out[1] = oy;
        return d - r;
    }

    const x1 = r * Math.cos(startAngle) + cx;
    const y1 = r * Math.sin(startAngle) + cy;

    const x2 = r * Math.cos(endAngle) + cx;
    const y2 = r * Math.sin(endAngle) + cy;

    const d1 = (x1 - x) * (x1 - x) + (y1 - y) * (y1 - y);
    const d2 = (x2 - x) * (x2 - x) + (y2 - y) * (y2 - y);

    if (d1 < d2) {
        out[0] = x1;
        out[1] = y1;