I was curious about how an instantly disappearing 'vapor beam' would look so I created a small mock-up:
I've done it too. But wanted to wait for some time before posting it, so to not bother the Meridian in a quick succession of time.
Just a note to your example: if you set the "vaporProbabilitySurface" to 100 and "vaporDensitySurface" to 4-6 - it will look more concentrated, i.e. "beam like". I forgot to do it myself when I was doing mine example.
Here is how it will look like with the "vaporProbabilitySurface: 100" and "vaporDensitySurface: 4".
And here is my example (in which I also forgot to change those two values):
Out of my proposed values: there is a very small dissipation delay (so you can see the trail stays on full opacity for some time before starting to fade out), medium dissipation (fade out) speed (faster than the regular vapor) and no vapor movement speed (so the cloud stays stationary until the end).
Also I'm not sure if I was able to convey my thoughts properly, because of the language barrier, the usage of the wrong terms and my complete lack of knowledge on how the vapor animation works, so I will try to do it again and I hope better this time. Not for the sake of persuading you, just to better explain myself.
I'm sorry if you understood everything the first time and now I'm just wasting your time.
There is no transparency or opacity gradient in OpenXcom.
Right now in the game the vapor cloud fades out, it is not permanent, right? And it does this not by instantly going from "particle exists" to "particle doesn't exist", but by slowly losing "opacity" (I don't know how exactly this is called and works, so excuse my choice of words) in a span of couple of seconds. This is the "dissipation" or "fade out" which I mean. And I mean editing the delay and speed of this fade out animation, as well as movement speed of the particles in it.
Also, why on earth would I simulate a beam by a non-moving vapor cloud? That's like flying from London to Paris via Tokyo.
PS: there is already a request for beams: https://openxcom.org/forum/index.php/topic,9968.0.html
The first reason, is that I thought that it will require less work and time to modify an existing system, than to create a new one (a beam animation system, in this case).
The second reason, is that I thought that those additions will be beneficial for tweaking the vapor clouds overall (can't think of an example tho, sorry), even if we are not talking about the simulation of beams, but you will also receive an option (maybe not an ideal one) to simulate beams, to some extent at least, until the creation of their own animation system, if it happens.
Well yeah, it will be not an ideal "beam", but it's at least something. But I absolutely wouldn't argue if you say that it requires more than enough work for a very questionable benefit - I just don't know how much work it requires.
And again, thanks for your attention and sorry for taking even more of your time.