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2019-08-22 17:43 UTC

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IDProjectCategoryView StatusLast Update
0002050OpenClonkObjectspublic2019-01-20 19:09
ReporterMarky 
Assigned To 
PrioritynormalSeverityminorReproducibilityalways
StatusnewResolutionopen 
Product Version 
Target VersionFixed in Version 
Summary0002050: Behaviour of smoke with non-standard gravity
DescriptionI think that my commit yesterday does actually NOT produce 'correct' smoke behaviour: https://github.com/openclonk/openclonk/commit/94e200f201596ab09b8642a6bea863bfddaa44d0

Correct is: F_up = <density of atmosphere> * <volume of smoke> * <gravity acceleration>

Also, particles have no downward force by default, which means that we have to factor in F_down = <density of smoke> * <volume of smoke> * <gravity acceleration>

So F_total = F_down - F_up = <gravity acceleration> * <volume of smoke> (<density of smoke> - <density of atmosphere)>

which means that the original implementation was closer to correct than I thought?
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~0006199

Zapper (developer)

Your commit says you are now using a "starting value". The documentation says that the second parameter is a constant summand. Is that what you intended?

Before it was <gravity> * (-100 + heavy*90) + 0 and now it's
<gravity> * (100 + heavy*90) - 10.

Did you test your commit? It looks like a big change and really odd.

And what is the problem with non-standard gravity? I can't tell from your bug report, maybe explain what you intend and I can help :)
Also I can't tell what "correct" means in this context

~0006200

Marky (developer)

I tested the commit, an it behaves as I want to, but we had a discussion in #openclonk-dev what is physically correct.

Back to the original implementation and my problem with it: When gravity is 50% of default gravity, then smoke used to go about 50% as high, but I'd expect it to fly higher actually (from non-physically thinking intuition). Analogous, if gravity is 200% and everything falls down faster, smoke flies double as high.

However, it seems that the original implementation is actually correct, and my implementation is incorrect.
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-Issue History
Date Modified Username Field Change
2018-12-28 08:50 Marky New Issue
2019-01-14 14:44 Zapper Note Added: 0006199
2019-01-20 19:09 Marky Note Added: 0006200
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