Oolite Bulletins

Posted: **Wed Dec 17, 2008 7:54 am**

For my q-bomb OXP I would like defunct q-bombs to just sit there. But I can't make it.

When I eject a q-bomb it gets a certain velocity, inherited from my own ship. If I stand still, its backwards velocity is biggest. I I fly forward, the bomb's velocity is smaller.

However, while moving away from me, it officially has a speed of 0.

> player.ship.target.speed
0

is what the console says, despite of the bomb's high velocity.

Now I've got a problem. How do I stop something which for scripting purposes has a speed of 0, while in reality it moves fast? setSpeedTo: 0 doesn't work (speed is already 0), same for setSpeedFactorTo: 0. Also performHold brought me no luck.

Oh, and I already changed its thrust from 0 to positive values. First I tried 10, then 50, then 1000. To no avail.

What else can I do to make it stop? How does it work for escape pods? Doesn't their inherited injection speed drop to 0 after a while and is replaced by their engines' speed?

Posted: **Wed Dec 17, 2008 9:37 am**

Unfortunately, there’s a distinction between engine-controlled speed and physics-controlled velocity. Ships generally compensate for non-zero velocity by thrusting in the opposite direction, which is what you’re seeing with the escape pods. Q-bombs have zero thrust, though, so they just drift. There’s currently no way to give just some q-bombs non-zero thrust unless you can use separate shipdata entries.

Posted: **Wed Dec 17, 2008 9:41 am**

As far as I remember from the code, a ship can have two kinds of "speeds". The speed that is defined in shipdata and scripting. That is always in flying direction. Than there is a "velocity". This is actually a vector that contains a ships actual speed and direction. e.g. when missiles are launched they have a forward speed but also a velocity downwards. This velocity is the actual movement. Speed is internally transferred into velocity (Is makes sense as speed is not just a number but a vector with direction)

From the code of ejecting a bomb:

Code: Select all

	double  eject_speed = -800.0;
	vel = vector_multiply_scalar(v_forward, [self flightSpeed] + eject_speed);
	eject_speed *= 0.5 * (randf() - 0.5);   //  -0.25x .. +0.25x
	vel = vector_add(vel, vector_multiply_scalar(v_up, eject_speed));
	eject_speed *= 0.5 * (randf() - 0.5);   //  -0.0625x .. +0.0625x
	vel = vector_add(vel, vector_multiply_scalar(v_right, eject_speed));

Its a little bit cryptic, but the names probably already give a rough idea of what happens.

But to your speed reduction: A ship needs trust to reduce its speed. With a trust of zero it still will remain its speed even when max speed is zero. In my experience a trust around the 15 gives a nice slowdown until max speed is reached. AI commands are not needed as the system always will try to slow down the stuff to max speed.

Your method should work. I don't see anything in the code that is overruling a previous trust setting.

Posted: **Wed Dec 17, 2008 10:24 am**

@ Ahruman: Currently I opted for giving all q-bombs thrust via shipdata-overrides.plist.

But it doesn't work even with a thrust of 1000, inferred upon the q-bomb this way.

Question: In timebombAI I just set the speed to 0 if the bomb is defused. Then I inserted a pauseAI:, because I thought there is perhaps some time needed to let it come into effect. So it looks like this:

Code: Select all

    "CHECK_FOR_MASS" = {
        DEFUSE = ("setSpeedTo: 0.0", "pauseAI: 5.0"); 
        DETONATE = (becomeEnergyBlast); 
        ENTER = ("sendScriptMessage: checkForPlanetProximity"); 
        UPDATE = (becomeUncontrolledThargon); 
    };

Now to my question: Do I perhaps need some perform... method as well, to make the setSpeedTo: effective?

Posted: **Wed Dec 17, 2008 3:34 pm**

performStop maybe in AI? becomeUncontrolledThargon should also work. My minesweepers tell any nasty ordinance they find to becomeUncontrolledThargon by way of a scipt action and in playtesting Cascade Missiles just stop and spin when they are turned into uncontrolled Thargons.

Posted: **Thu Dec 18, 2008 6:38 am**

Sorry to Ahruman and Eric! Everything's working perfect, the only buggy factor was, ahem..., me.

For some reason that I don't recall the shipdata-overrides or shipdata I wrote into was not from the OXP version in my AddOns, but from a development version stored elsewhere. So all my changes of cargo_type and thrust simply weren't incorporated in the game. Oops!

When I finally realized this and opened the correct file(s), everything worked like a charm.

After some tests qnd playing with different values I did not go for substituting the defused qbomb with a clone, but gave it a thrust of 15. This will bring it to a halt in a sufficient amount of time (and no setSpeedTo: or the like are even needed). Warning: This means that the qbomb will slowly decelerate from the moment it is dumped, so it will explode a little closer to the dumper. However, with a thrust of 15 the difference is not very big.

Oolite Bulletins

how to stop something that has speed 0?

how to stop something that has speed 0?