Control cell boost direction

epstein.js

boostCell(cell) {
    const d = cell.boost.d / 9 * this.handle.stepMult;
    if (cell.owner !== null) {
        let dx = cell.owner.router.mouseX - cell.x;
        let dy = cell.owner.router.mouseY - cell.y;
        let d0 = Math.sqrt(dx * dx + dy * dy);
        if (d0 < 1) {
            dx = 1;
            dy = 0;
        } else {
            dx /= d0;
            dy /= d0;
        }
        cell.boost.dx = dx;
        cell.boost.dy = dy;
    }
    cell.x += cell.boost.dx * d;
    cell.y += cell.boost.dy * d;
    this.bounceCell(cell, true);
    this.updateCell(cell);
    if ((cell.boost.d -= d) >= 1) return true;
    this.setCellAsNotBoosting(cell);
    return false;
}