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Version 2.42.6 Released

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Numsgil:
In 2.4 I made bouyancy a function of volume, as you would expect in real life.  The problem is the only thing bots have that effect their density, and hence bouyancy, is shell and body.
 
 If there isn't any fluid density, there won't be any fluid bouyancy.

PurpleYouko:

--- Quote ---In 2.4 I made bouyancy a function of volume, as you would expect in real life.
--- End quote ---
I wouldn't expect that at all.

Whales are huge and have neutral bouyancy at the surface and somewhat negative bouyancy as they dive to great depths as the air in their lungs gets compressed.

Tiny little crabs sink like a rock.

Fishes of all sizes are able to float up and down at will by the use of swim bladders. That is what bouyancy is supposed to represent


--- Quote ---The problem is the only thing bots have that effect their density, and hence bouyancy, is shell and body.
--- End quote ---
Not true. I gave them swim bladders in the form of the .setboy sysvar.


--- Quote ---If there isn't any fluid density, there won't be any fluid bouyancy.
--- End quote ---
Fluid density in pond mode is assumed to be that of water. It is a fixed and completely irrelevent value and is constant with depth. We don't need it to be defined beyond that.
The default position of all bots of any size is neutral bouyancy but this can be changed by internal adjustments (swim bladder) or external adjustments like the addition of shell which would obviously make them more dense.

Where exactly is the problem. This was completely working in 2.37.6 and what's more it was very simple and elegent.  

Numsgil:

--- Quote from: PurpleYouko ---I wouldn't expect that at all.

Whales are huge and have neutral bouyancy at the surface and somewhat negative bouyancy as they dive to great depths as the air in their lungs gets compressed.

Tiny little crabs sink like a rock.

Fishes of all sizes are able to float up and down at will by the use of swim bladders. That is what bouyancy is supposed to represent
--- End quote ---

 All those things are on Earth and hence are also being acted upon by gravity.  The net movement in a liquid is a function of bouyancy and weight of the object (although bouyancy wouldn't exist in a zero G environment either).
 
 Hence, the net movement of an object is actually dependant upon density.  Bouyancy, however, is strictly dependant on volume.  (Force of Bouyancy = Volume * density of liquid * gravity, ie: Archimedean Principle)


--- Quote ---Not true. I gave them swim bladders in the form of the .setboy sysvar.
--- End quote ---

 Which I couldn't figure exactly what to do with when I remade bouyancy.  I mentioned this at one point when I talked about adding a new constructable unit which would be massless but take up volume, to help counter shell which can be used as a balast (no volume, but adds mass), but I couldn't reach a concensus, so I put it on hold and apparently forgot about it.


--- Quote ---Fluid density in pond mode is assumed to be that of water. It is a fixed and completely irrelevent value and is constant with depth. We don't need it to be defined beyond that.
--- End quote ---

 1.  Liquid can't be compressed, so it's density is constant at all depths.  Pressure, however, is not, which I assume is what you're confusing it with.  Since bots are assumed to be implosion-proof, pressure obviously doesn't matter.
 
 2.  It should be fairly obvious that you can define the density of the liquid since the advanced physics tab has a field where you can specify the density of the liquid.  In fact, if you read the toolbar in the advanced physics tab it tells you that density effects the force of bouyancy.  It also tells you the density of an average bot for comparison purposes.
 
 3.  "water" has no correlation with the bot universe because we have nothing to compare any of the metrics between the two environments with.  Density in real life is (kilo)grams / meter^3.  Density in DB is mass / twip^3.  It's comparing apples and oranges.
 
 
--- Quote ---The default position of all bots of any size is neutral bouyancy but this can be changed by internal adjustments (swim bladder) or external adjustments like the addition of shell which would obviously make them more dense.
--- End quote ---

 Assuming a density of 1E-6 (which advanced physics tab suggests), this is true (minus the swim bladder, which I explained above).  1E-6 should be the density of body.  Adding shell would make you sink.  There's nothing you can add to decrease density, which is the problem I explained above.


--- Quote ---Where exactly is the problem. This was completely working in 2.37.6 and what's more it was very simple and elegent.  
--- End quote ---

 It was perhaps simple but it did not correlate well with the rest of the physics.  By redoing all the physics, I tied all forces in together to create a central and stable way to integrate them.  By tying bouyancy in to fluid density, I correlated drag forces, bouyancy, etc. into a few parameters which correspond very well with real life.

PurpleYouko:

--- Quote ---All those things are on Earth and hence are also being acted upon by gravity. The net movement in a liquid is a function of bouyancy and weight of the object (although bouyancy wouldn't exist in a zero G environment either).
--- End quote ---
And so is "pond" mode. It represents a pond after all. You cann't have a pond unless you have gravity so the concept of a pond automatically assumes its presence.


--- Quote ---Hence, the net movement of an object is actually dependant upon density. Bouyancy, however, is strictly dependant on volume. (Force of Bouyancy = Volume * density of liquid * gravity, ie: Archimedean Principle)
--- End quote ---
Except that archimedies principle is irrelevent when it is applied to aquatic creatures which swim in the water column. Their density is identical to the medium through which they swim as a default. They can change it with the addition of more dense stuff like shells or less dense stuff like swim bladders..


--- Quote ---Which I couldn't figure exactly what to do with when I remade bouyancy. I mentioned this at one point when I talked about adding a new constructable unit which would be massless but take up volume, to help counter shell which can be used as a balast (no volume, but adds mass), but I couldn't reach a concensus, so I put it on hold and apparently forgot about it.
--- End quote ---
I don't even remember this but then I really didn't have a great deal to do with 2.4 most of the time


--- Quote ---1. Liquid can't be compressed, so it's density is constant at all depths. Pressure, however, is not, which I assume is what you're confusing it with. Since bots are assumed to be implosion-proof, pressure obviously doesn't matter.
--- End quote ---
I'm not confusing anything. I stated that density of water is constant with depth and it is. I didn't mention pressure since any creature living at any depth will take on the density of its surrounding water. It is irrelevent as I said.


--- Quote ---In fact, if you read the toolbar in the advanced physics tab it tells you that density effects the force of bouyancy. It also tells you the density of an average bot for comparison purposes.
--- End quote ---
That's all very fine and dandy except that in "Pond Mode" all that stuff should be totally over-ridden such that bot density == water density. Otherwise the concept of "Pond Mode" is a waste of space. Gravity is also a meaningless concept in "Pond Mode". All you need to know is that it exists. Any change in its magnitude will only serve to change the pressure acting throughout the whole system and since the robots and the water exist in a complete balance, nothing will change at all.


--- Quote ---3. "water" has no correlation with the bot universe because we have nothing to compare any of the metrics between the two environments with. Density in real life is (kilo)grams / meter^3. Density in DB is mass / twip^3. It's comparing apples and oranges.
--- End quote ---
The exact density is utterly irrelevent. The math to calculate it is utterly irrelevent. The differences between the DB world and the real world are also utterly irrelevent.
There is only one thing here that is an issue of any kind.
"Pond Mode" was created to simulate a POND or TANK with all assumptions relating to water and bot density automatically implied. Equally, in "Pond Mode" the Y axis of the screen can only be equated to up and down in the vertical plane so many other assumptions are implied also.


--- Quote ---Assuming a density of 1E-6 (which advanced physics tab suggests), this is true (minus the swim bladder, which I explained above). 1E-6 should be the density of body. Adding shell would make you sink.
--- End quote ---
Yup. That's right.

--- Quote ---There's nothing you can add to decrease density, which is the problem I explained above.
--- End quote ---
Except that there quite obviously IS.
Fish do it all the time.
It's called a SWIM BLADDER. Fish are able to manipulate their density to float up or sink down at will. Plankton do it too. As do krill and many other aquatic creatures.


--- Quote ---It was perhaps simple but it did not correlate well with the rest of the physics. By redoing all the physics, I tied all forces in together to create a central and stable way to integrate them. By tying bouyancy in to fluid density, I correlated drag forces, bouyancy, etc. into a few parameters which correspond very well with real life.
--- End quote ---
It didn't need to correlate with much of the other physics. It was designed to override them.
Frankly I have never really liked the physics of 2.4 much. That's another reason why I have still not made the switch.

The fact is that in almost every way that matters to me, 3.37.6 is still superior. 2.4 is getting better but it just lacks all the things that make DB fun for me.

Numsgil:

--- Quote from: PurpleYouko ---Except that archimedies principle is irrelevent when it is applied to aquatic creatures which swim in the water column. Their density is identical to the medium through which they swim as a default. They can change it with the addition of more dense stuff like shells or less dense stuff like swim bladders..
--- End quote ---

 This is not exactly true.  Most fish are not in equilibrium density with their environment.
 
 Swim bladders are not found in all fish.   Many cartilaginous fish, such as sharks, can control their depth only by swimming; others store fats or oils for this purpose.
 
 
--- Quote ---I'm not confusing anything. I stated that density of water is constant with depth and it is. I didn't mention pressure since any creature living at any depth will take on the density of its surrounding water. It is irrelevent as I said.
--- End quote ---

 I'm sorry, I read consistant instead of constant.  Changed the meaning of the whole sentence.


--- Quote ---That's all very fine and dandy except that in "Pond Mode" all that stuff should be totally over-ridden such that bot density == water density.  Otherwise the concept of "Pond Mode" is a waste of space.
--- End quote ---

 At present pond mode implies only the way in which light is distributed in the sim.  What if I want to run a sim with a gradient for the vegs in a total vacuum?  I'm certain I mentioned this when I split corpse mode and pond mode apart into their most core features.  I removed the hooks to the other concepts (such as gravity) in order to allow the end user greater freedom in simulation parameters.
 
 
--- Quote ---Gravity is also a meaningless concept in "Pond Mode". All you need to know is that it exists. Any change in its magnitude will only serve to change the pressure acting throughout the whole system and since the robots and the water exist in a complete balance, nothing will change at all.
--- End quote ---

 No.  Net forces acting on a body in a liquid = Force of Bouyancy - Force of Gravity = Volume of object * density of liquid * gravity - mass * gravity = gravity * (Volume * density - mass)
 
 Gravity doesn't cancel out.  Having more gravity will increase the magnitude of the resulting force.  Objects that float upwards at X meters per second on Earth will float X/6 meters per second on the moon.


--- Quote ---It's called a SWIM BLADDER. Fish are able to manipulate their density to float up or sink down at will. Plankton do it too. As do krill and many other aquatic creatures.
--- End quote ---

 I meant in the DB universe there's nothing to construct to make you less dense.  And while we're on the subject, swim bladders have a whole set of gotchas and consequences fish have to deal with.  Among them they'd explode if they tried to rise too quickly.
 
 
--- Quote ---It didn't need to correlate with much of the other physics. It was designed to override them.
--- End quote ---

 Override the physics system or override the physics constants?  Those are two very different things.
 
 
--- Quote ---Frankly I have never really liked the physics of 2.4 much. That's another reason why I have still not made the switch.
--- End quote ---

 I'm sorry you feel like this, but most everyone else I've heard comment on them feels they are a step in the right direction.  The problem is that they're almost realistic, so people are better able spot discrepancies with real life.  The older physics was so absolutely unrealistic you could never really compare it with real life so its flaws were a little better masked.
 
 Do various stress test comparisons between 2.4 and 2.37.  1000 veggies with some gravity for instance.  Or several bots that tie to everything they can.  I think you'll see my point.

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