Function limitTurnAngle

src/label/labelGuideHelper.ts:411–461

(linePoints: number[][], minTurnAngle: number)

 * @param minTurnAngle Radian of minimum turn angle. 0 - 180
 */
export function limitTurnAngle(linePoints: number[][], minTurnAngle: number) {
    if (!(minTurnAngle <= 180 && minTurnAngle > 0)) {
        return;
    }
    minTurnAngle = minTurnAngle / 180 * Math.PI;
    // The line points can be
    //      /pt1----pt2 (label)
    //     /
    // pt0/
    pt0.fromArray(linePoints[0]);
    pt1.fromArray(linePoints[1]);
    pt2.fromArray(linePoints[2]);

    Point.sub(dir, pt0, pt1);
    Point.sub(dir2, pt2, pt1);

    const len1 = dir.len();
    const len2 = dir2.len();
    if (len1 < 1e-3 || len2 < 1e-3) {
        return;
    }

    dir.scale(1 / len1);
    dir2.scale(1 / len2);

    const angleCos = dir.dot(dir2);
    const minTurnAngleCos = Math.cos(minTurnAngle);
    if (minTurnAngleCos < angleCos) {    // Smaller than minTurnAngle
        // Calculate project point of pt0 on pt1-pt2
        const d = projectPointToLine(pt1.x, pt1.y, pt2.x, pt2.y, pt0.x, pt0.y, tmpArr, false);
        tmpProjPoint.fromArray(tmpArr);
        // Calculate new projected length with limited minTurnAngle and get the new connect point
        tmpProjPoint.scaleAndAdd(dir2, d / Math.tan(Math.PI - minTurnAngle));
        // Limit the new calculated connect point between pt1 and pt2.
        const t = pt2.x !== pt1.x
            ? (tmpProjPoint.x - pt1.x) / (pt2.x - pt1.x)
            : (tmpProjPoint.y - pt1.y) / (pt2.y - pt1.y);
        if (isNaN(t)) {
            return;
        }

        if (t < 0) {
            Point.copy(tmpProjPoint, pt1);
        }
        else if (t > 1) {
            Point.copy(tmpProjPoint, pt2);
        }

        tmpProjPoint.toArray(linePoints[1]);
    }
}

/**
 * Limit the angle of line and the surface