How is the escape time of UFOs scaled?


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#1 magic9mushroom

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Posted 21 July 2018 - 03:11 AM

I know the values for UFO escape time in GEOSCAPE.EXE. However, I'm certain that they're reduced by some factor related to the difficulty level. I know this because I've tested Stingray Interceptor vs. Small Scout on both Beginner and Superhuman; on Beginner the Interceptor always gets to fire at least one Stingray (as you'd expect, as the Small Scout's escape time is 200 and it only takes 180 frames to close from 75km to 30km), on Superhuman the Small Scout will usually escape (~70%?) before any Stingrays are fired.

I'm guessing that, much like UFO reload times, this is a simple "reduce escape time by X * difficulty multiplier", with X = 20 or 25, but I'd like to be sure before I update the UFOpaedia.

EDIT: Did a test with a Plasma Beam Interceptor vs. Small Scout on Superhuman; there's a very small chance (~10%?) that the Small Scout will run just before the Plasma Beams can take a shot. So the minimum escape time on Superhuman appears to be slightly under 92 frames (the time from 75km to 52km; I clicked Aggressive Attack before it reached 70km to avoid a pause). That's quite a wide spread (under 92 to over 180 would seem to rule out a 100-200% range).

EDIT2: Tested with a Cannon on Superhuman, and got a rather interesting result. The Small Scout, of course, nearly always runs before coming into Cannon range, but it is possible to get a shot. Singular. In a very small number of cases, the Interceptor gets a single shot, basically simultaneous with "UFO OUTRUNNING INTERCEPTOR!" showing up. So the maximum is pretty much nailed down at almost exactly the time to reach Cannon range, which would appear to be 260 frames (75km to 10km).

#2 NKF

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Posted 21 July 2018 - 06:39 AM

After a little digging around the sequel.... it seems to be:

UFO escape time - (Difficulty * 30) + Random number between 0 and UFO escape time

Difficulty will be the same difficulty level value that is used for calculating stats. So a Small Scout should escape on beginner (diff: 0) between 200 - 400 and on superhuman (diff: 4) around 80 - 280.

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#3 magic9mushroom

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Posted 21 July 2018 - 08:51 AM

View PostNKF, on 21 July 2018 - 06:39 AM, said:

After a little digging around the sequel.... it seems to be:

UFO escape time - (Difficulty * 30) + Random number between 0 and UFO escape time

Difficulty will be the same difficulty level value that is used for calculating stats. So a Small Scout should escape on beginner (diff: 0) between 200 - 400 and on superhuman (diff: 4) around 80 - 280.

- NKF

That fits nigh-perfectly, though only when taking into account something I just learned from deliberately lagging the game to get a frame-by-frame look. Specifically, interception starts at 80km (640 range units), NOT 75km as the UFOpaedia says.

So to close to 52km (Plasma Beam range) takes 112 frames, giving the Small Scout a 15.9% chance to run before the first shot. To close to 30km (Stingray range) takes 200 frames, giving the Small Scout a 59.7% chance to run before the first shot (although since the Stingray takes a significant time to reach its target, it may run before the missile hits). And to close to 10km (Cannon range) takes 280 frames, giving a mere 0.5% chance that an Interceptor with Cannons will get to fire (it won't hit, though, since the Small Scout runs at exactly the same frame the Cannon fires).


Among other things I've discovered from exhaustively testing interception: a mutual kill is possible. That is, it's possible that the X-Com craft is destroyed and the UFO crashes (leaving a Crash Site and no X-Com craft after the interception window closes). Found that out when pitting a Firestorm against a Battleship a few dozen times.




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