Region of scr_fire_cannon

#region // create shell object and initialize its direction and theta
shell = instance_create(shell_x,
                        shell_y,
                        shell_object);

with (shell) {

    // assign bullet owner to ensure it doesn't hit self
    owner = other.owner;

    // give bullet its direction
    image_angle = other.image_angle;
    direction = image_angle;

    // for calculating travel distances, get origin and target x, y, z locations
    origin_y = y;
    origin_x = x;
    origin_z = other.z;

    target_x = other.desired_point[0];
    target_y = other.desired_point[1];
    target_z = other.desired_point[2];

    // set target distance
    target_distance = point_distance(x, y, other.desired_point[0], other.desired_point[1]);

    // make sure distance isn't greater than maximum
    if (target_distance > other.maximum_range) target_distance = other.maximum_range;

    show_debug_message("Target distance: " + string(target_distance));

    // shells total velocity in all axises
    shell_velocity = other.shell_velocity;

    // use for testing purposes, delete when formulas work
    target_z = 40;

    // convert velocity from pixels per tick to pixels per second
    var v = shell_velocity * room_speed; // convert speed per tick to speed per second

    // v to the power of 2
    var v_2 = power(v, 2);

    // v to the power of 4
    var v_4 = power(v, 4);

    // gravity
    var g = 9.8 * 10;

    // displacement to target in vertical and horizontal
    var dis_h = target_distance;
    var dis_v = (target_z - origin_z);
    var dis_h_2 = power(dis_h, 2);

    // calculate potential angles, one will be high, one will be low
    var theta_0 = radtodeg(arctan(  (v_2 - sqrt(v_4 - g * ( g * dis_h_2 + 2 * dis_v * v_2)) ) / (g * dis_h)   ));
    var theta_1 = radtodeg(arctan(  (v_2 + sqrt(v_4 - g * ( g * dis_h_2 + 2 * dis_v * v_2)) ) / (g * dis_h)   ));

    // set to angle closest to 0
    if (abs(theta_1) < abs(theta_0)) theta = theta_1;
    else theta = theta_0;

    show_debug_message("Theta is: " + string(theta) + " based on a theta_0 of: " + string(theta_0) +
        " and theta_1 of: " + string(theta_1));

    // horizontal velocity, x and y axis
    velocity_h = shell_velocity * radtodeg(cos(degtorad(theta)));

    // vertical velocity, z axis
    velocity_v = shell_velocity * radtodeg(sin(degtorad(theta)));
}

#endregion