Meta talk:Sandbox/Physics/Soft Bodies

Attribution

I have taken a lot of text from Doc:Manual/Physics/Soft Bodies. See that pages history for all contributers. Authors have been (in chronological order):

• Ewout
• Sprite
• Bjornmose
• Halley
• Hoehrer
• Oninoshiko
• Broken
• Roger
• Remi
• Kolban
• Iaminnocent
• Mppic

I seems to me that Roger had the greatest share at it. Thanks to all of you. --Soylentgreen 09:39, 9 April 2009 (UTC)

Corrections [1]

Hi!

To what degree would you like me to go with corrections? Should I just focus mainly on ensuring that a piece of text can be understood or would you like me to go deeper.

For instance, if I were doing detailed correction my instinct would be to change the following text:

" A Soft Body is really a physical simulation of what would happen "in the real world" if an object actually had substance and was a real "thing". Using Soft Bodies, you can simulate the shapes that an object would take on if it was real and have volume, was filled with something inside of it, and was acted on by real forces. But its a simulation, so don't forget: the primary targets of the simulation are the vertices of the object, they react to the forces (exterior forces). The vertices hold together with their connecting edges or virtual edges (interior forces). "

to:

" A Soft Body is a physical simulation of what would happen to an object if it were to exist "in the real world". Using Soft Bodies, you can simulate the shapes that an object would take on in reality if it had volume, was filled with something, and was acted on by real forces. During the physical simulation the primary objective is to adjust an object's vertices as they react to exterior forces. However, vertices will continue to hold together and try to maintain their original shape based on the interior forces that you define for them. "

Is that going to far?

Hogus 12:03, 22 April 2009

No, the changes are good. But I think we need more changes. The emphasis has to be made that everything is calculated for the vertices. I think it should be something like:

A Soft Body is a physical simulation of what would happen to an object if it were to exist "in the real world". This is done by applying forces to the vertices or controlpoints of the object. There are exterior forces like gravity or forcefields and interior forces that hold the vertices together. This way you can simulate the shapes that an object would take on in reality if it had volume, was filled with something, and was acted on by real forces.

--Soylentgreen 12:26, 22 April 2009 (UTC)

Yes, that sounds even better, and it's shorter.

I'm busy reading through everything and making notes, but I'm still running 2.48 , Is there a binary download somewhere for 2.49RC1?

--Hogus 07:30, 23 April 2009

You can try one of those [1]. I'm not quite sure which is the most recent version, since I'm compiling daily from SVN. It may be this one [2] --Soylentgreen 08:31, 23 April 2009 (UTC)

Ok, I'll look for the correct one when I get back, in the mean time here are some more comments: --Hogus

Thank you for all your suggestions, I have included everything I totally agree with or know how to put it better already. :-) --Soylentgreen 15:32, 23 April 2009 (UTC)

Corrections [2]

My comments on the following section:

---

• If you drop a vertex it falls down (gravitation).
• If a wind blows or another force is active this force will move the the vertices.
• The acceleration of a vertex depends on its weight, heavy vertices accelerate slower than light vertices.
• Movement is slowed down by friction.
• If you hold a vertex it will not move (Goal).
• The vertices hold together through their connecting edges.

Soft Bodies can interact with other objects (Collision). They can interact with themselves (Self Collision).

The result of the Soft Body simulation can be converted to a static object. You can also bake edit the simulation, i.e. edit intermediate results and run the simulation from there.

---

[This seems like a very disorganized introduction and the selected excerpts off the functionality seem a bit random, it should better align with the content that will be presented below]

I have removed the greater part of it.

Corrections [3]

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Soft Bodies are well suited for:

• elastic objects with and without collision
• flags, fabric reacting to forces
• certain modeling tasks, like a cushion or a table cloth over an object
• clothing? This is possible but not so easy, there is a reason that Blender has another simulation system for clothing (see Clothes). But you can use Soft Bodies for certain parts of clothing, like wide sleeves.
• hair, as long as you minimize collision
• animation of swinging ropes, chains and the like

A few ideas of what is possible with Soft Bodies are shown with these videos:

---

Soft Bodies are well suited for:

• Elastic objects with or without collision.
• Flags, fabric reacting to forces.
• [We need to dig deeper here to define the kind of task we mean] certain modeling tasks, like a cushion or a table cloth over an object.
• Blender has another simulation system for clothing (see Clothes). But you can sometimes use Soft Bodies for certain parts of clothing, like wide sleeves.
• Hair (As long as you minimize collision).
• Animation of swinging ropes, chains and the like.

The following videos may give you some more ideas:

I have used your suggestions, it may be useful to explain the modeling part better.

Corrections [4]

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Soft Body simulation works for all objects that have vertices resp. control points:

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The abbreviation "resp." is confusing. What exactly is meant by it?

or

Corrections [5]

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To make a Soft Body out of an object:

• change to the Object buttons in the Physics sub context
• activate the button Soft Body in the Soft Body panel (Img. 2a). For a hair particle system first select the particle system, than activate Soft Body (Img. 2b).

---

To enable Soft Body modifiers on an object:

• Change to the object context (F7), and select "Physics Buttons".
• Activate the button Soft Body in the Soft Body panel (Img. 2a).
• For a hair particle system first select the particle system, than activate Soft Body (Img. 2b).

changed that

Corrections [6]

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Soft Bodies use a unified system for caching and baking (together with cloth and particles). The results of the simulation are automatically cached to disk when the animation is played, so that the next time it runs, it can play again quickly by reading in the results from the disk. If you Bake the simulation the cache is protected and you will be asked when you're trying to change a setting that will make a recalculating necessary.

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[Note to myself: Work on editing this, after running a few simulations on 2.49]

Works as on 2.48a

Corrections [7]

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	Beware of the Start and End Settings
	The simulation is only calculated for the positive frames in-between the Start and End frames of the Bake panel, whether you bake or not. So if you want a simulation longer than 250 frames you have to change the End frame!

---

	Beware of the Start and End Settings
	The simulation is calculated - in a forward direction - for frames between the Start and End setting on the Bake panel, even if you don't actually bake the simulation! So if you want a simulation longer than the default setting of 250 frames you have the change the End frame.

Changed that. The part about "positive frames" is not necessary for softbodys.

Corrections [8]

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• If it is impossible to write in the subdirectory there will be no caching.

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• If you are not allowed to write to the required sub-directory caching will not take place.

Changed that

Corrections [9]

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• The cache can be freed per physics system with a button in the panels, or with the Ctrl B shortcut key to free it for all selected objects.

---

[Note to self: would like to test this on 2.49]

Works as in 2.48a

Corrections [10]

• If the file path to the cache is longer than what it's possible with your operating system (more than 250 characters for example), there may happen strange things.

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• If your operating system does not support path lengths long enough for the path that is required to cache your simulation, strange things may happen

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[or]

• If for example your operating system only supports path lengths up to 250 characters and the path length required to cache your simulation is longer than that, strange things may happen.

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[or]

• You may run into trouble if your .blend file path is very long and your operating system has a limit on the path length that is supported.

changed that

Corrections [11]

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Baking

• The system is protected against changes after baking.
• The Bake result is cleared also with CtrlB for all selected objects or click on Free Bake for a singular particle system.
• If the mesh changes the simulation is not calculated anew.

---

Baking

• The cache is protected against changes after baking. So you may not see any changes to the physics simulation even if you do make a change that should produce a different result.
• You can use CtrlB to clear the bake result for all selected objects or click on "Free Bake" ?for a singular particle system?[Why only for a singular particle system?Maybe we mean the current particle system, or the current SoftBody instead?].

for the current system. Changed that

Corrections [12]

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For renderfarms, it is best to bake all the physics systems, and then copy the blendcache to the renderfarm as well.

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[Make this a note (perhaps with a reference), since the reader might have no idea about renderfarms yet]

Have not changed that yet, but may be a good idea.

Corrections [13]

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To work with a Soft Body simulation you will find it handy to use the Timeline window. You can change between frames and the simulation will always be shown in the actual state.

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The Timeline window is useful when working with SoftBody simulations. [Not sure what is meant by, "simulation will always be shown in the actual state", are we trying to say that you can scrub along the timeline window to find the simulation's state for a particular frame?]

Corrections [14]

The option Continue Physics in the Playback menu of the Timeline window lets you interact in real time with the simulation, e.g. by moving collision objects or shake a Soft Body object. And this is real fun!

---

[I'm not sure how far we should go here in explaining this, or if we should rather leave most of this for a later section. This portion seems a little misleading. If I set up a basic tablecloth example, let it play out and pause it halfway through, the simulation will reset to it's frame zero position, if I grab the collision object and drag it. So this should either be described more thoroughly here, or it should be mentioned in passing, with a reference to a more detailed section...]

We should explain it here better. Else we would have to rewrite the Timeline page, and I don't want to do that.

Corrections [15]

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Use Soft Bodys only where it makes sense. If you try to cover a body mesh with a tight peace of cloth ...

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[should be "piece" of cloth, but we may also think of a better example here]

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I changed peace to piece, but maybe we should take the warnings out?

Okay, those are my comments for now, I'll start digging into the other sections after my holiday. -- Hogus 14:01, 23 April 2009