Hold-fire railguns not firing at target when railguns moving

Equalizer

There appears to be an issue that when hold-fire railguns are moving they can fail to fire when they are lined up with their target.

This is most obvious with ships that are supposed to spin.

Consider the following ship, when it is spinning the and the railguns are on hold fire they should fire at their given target as they rotate past it. However, once the ship is rotating at a moderate speed the railguns will often not fire.
image https://i.imgur.com/REGnmzE.png

Note: By running the railguns on auto fire it is clear that shots are moving fast enough to not impact the surround armor when spinning.

I assume this issues is caused by some form of target alignment check is too infrequent to detect the alignment.

mleise

Not sure if my spinner just turns faster than the <=90°/s the railguns need to reload. 🤔
In any case game physics are clocked. As far as I understand it there are big updates at 30 Hz and small ones at 120 Hz. If something spins sufficiently fast then yes, it might skip over a good alignment from one update to the next.
So if this is the reason, a fix could be to add a collision test of an invisible point at the target and an invisible line in front of the railgun. The physics engine would then tell the game that a collision occurred in the last time delta and the railgun would start to fire. Why this still isn't optimal:

The information is always delayed by up to the frequency of collision checks.
The railgun takes time to fire, so by the time the shot leaves the launcher, the target is way out of aim.
The rotation adds sideward momentum to the shot that makes it veer off target even more.

Lafiel

Physics simulation runs at 30 MHz max.

mleise

Lafiel On second read … I strongly doubt that it does 30,000 physics updates per millisecond.

Equalizer

mleise Walt previously mention that each weapon performs a raycast targeting check once per second.

Since this is quite slow it is not difficult for the alignment to be missed.

Walt

I'm pretty sure this is due to the fact that the physics simulation only runs at 30 ticks per second. So if a ship is spinning fast enough, then the railgun might simply never line up with its target.

Equalizer

Walt Any possibility to widen the target region with movement speed so that it can't be skipped over?

Walt

Equalizer Any possibility to widen the target region with movement speed so that it can't be skipped over?

That's a possibility. The result would be that the railgun shoots but hits something near its target instead of its actual target.

mleise

Walt Seems legit from a lore perspective. There is an additional problem with the timing of the shot that makes railgun spinners shoot too early. If that can be fixed in the process the overall accuracy might even improve. Here is an illustration.
T1: Spinner and target have no linear momentum. The railgun rotates at close to 90°/s and aims at the control room. It starts to fire before it is aligned to the target to compensate for its own movement:
image https://i.imgur.com/YQ2s2VI.png
T2: The shot leaves the launcher just before the railgun is fully aligned. It adds some downwards and a lot of backwards momentum to the shot.
image https://i.imgur.com/xPs2Mws.png
T3: The shot (consistently) hits a few tiles above the target.
image https://i.imgur.com/vagUOi6.png
image https://i.imgur.com/VdA9hW0.png

Oneye

Walt If this could make rail spinners more viable that would be great.

Alpha

Oneye There is still the railgun bug that has been mentioned earlier, it is annoying when buiding large ships. Should I make a new post about that, or do you think it has been noticed?

image https://i.imgur.com/VSecVsh.jpg

Oneye

Alpha I think you should make a new post about it.