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 --Elbrujodelatribu 13:10, 24 October 2012 (CEST)


Soft Bodies

Cuerpos Blandos

Imagen 1a: Una tela descubriendo un texto. AnimationBlend file

Un cuerpo blando o Soft Body en general, es una simulación de un objeto deformable rígido o blando. En Blender, este sistema es lo mejor para objetos de tela simples y mallas cerradas. Hay una física dedicada llamada Cloth Simulation que utiliza una solución diferente y es mejor para telas.

Esta simulación está hecha aplicando fuerzas a los vértices o puntos de control de un objeto. Hay fuerzas exteriores como la gravedad o campos de fuerza y fuerzas interiores que mantienen las partículas juntas. De este modo puede simular las formas que un objeto tendría en la realidad si tuviese volumen, estuviese relleno con algo, y se actuase sobre él por fuerzas reales.

Los cuerpos blandos pueden interactuar con otros objetos (Collision). Pueden interactuar con ellos mismos (Self Collision).

El resultado de la simulación de cuerpo blando se puede convertir en un objeto estático. También puede realizar el proceso bake edit sobre la simulación, por ejemplo, editar resultados intermedios y ejecutar la simulación desde ese punto.

Escenarios Típicos para la Utilización de Cuerpos Blandos

Imagen 1b: Un cono de viento. El cono es un cuerpo blando, como la suspensión. AnimationBlend file

Los cuerpos blandos son adecuados para:

  • Objetos elásticos con o sin colisión.
  • Banderas, tejidos reaccionando a fuerzad.
  • Ciertas tareas de modelado, como un cojín o un mantel sobre un objeto.
  • Blender tienen otro sistema de simulación para telas (vea Telas). Pero a veces puede usar Soft Body para ciertas partes de las telas, como las mangas.
  • Pelo (siempre y cuando se minimice la colisión).
  • Animación de cuerdas oscilantes, cadenas y similares.

Los siguientes videos pueden darle algunas ideas: [1], [2]

Crear un Cuerpo Blando

La simulación de cuerpos blandos funciona para todos los objetos que tienen vértices o puntos de control:

  • Mallas o Meshes.
  • Curvas o Curves.
  • Superficies o Surfaces.
  • Objetos enrejado o Lattice.

Para activar la simulación de cuerpo blando para un objeto:

  • En la ventana Properties, vaya a la pestaña Physics (está a la derecha del todo, y parece una pelota rebotando).
  • Active el botón Soft Body.

Aparecerán un montón de opciones. Para una referencia de todas las opciones vea esta página.

  • Puede empezar una simulación de cuerpo blando con AltA.
  • Puede pausar la simulación con Space, continuando con AltA.
  • Puede parar la simulación con Esc.


Calidad de la Simulación

The settings in the Soft Body Solver panel determine the accuracy of the simulation.

Min Step
Minimum simulation steps per frame. Increase this value, if the Soft Body misses fast moving collision objects.
Max Step
Maximum simulation steps per frame. Normally the number of simulation steps is set dynamically (with the Error Limit) but you have probably a good reason to change it.
Auto-Step
Use Velocities for automatic step sizes.
Error Limit
Rules the overall quality of the solution delivered. Default 0.1. The most critical setting that says how precise the solver should check for collisions. Start with a value that is 1/2 the average edge length. If there are visible errors, jitter, or over-exaggerated responses, decrease the value. The solver keeps track of how “bad” it is doing and the Error Limit causes the solver to do some “adaptive step sizing”.
Fuzzy
Simulation is faster, but less accurate.
Choke
Calms down (reduces the exit velocity of) a vertex or edge once it penetrates a collision mesh.

Diagnostics

Print Performance to Console
Prints on the console how the solver is doing.
Estimate Matrix
Estimate matrix. Split to COM , ROT ,SCALE


Caché y Bake

Soft Bodies and other physic simulations use a unified system for caching and baking. See Particle Cache for reference.

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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Beware of the Start and End settings
The simulation is only calculated for the frames in-between the Start and End frames (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.


  • Caching:
    • As animation is played, each physics system writes each frame to disk, between the simulation start and end frames. These files are stored in folders with prefix “blendcache”, next to the .blend file.
    • The cache is cleared automatically on changes - but not on all changes, so it may be necessary to free it manually, e.g. if you change a force field. Note that for the cache to fill up, one has to start playback before or on the frame that the simulation starts.
    • If you are not allowed to write to the required sub-directory caching will not take place.
    • The cache can be freed per physics system with a button in the panels, or with the CtrlB shortcut key to free it for all selected objects.
    • 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.
  • 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 the current Soft Body system.
    • If the mesh changes the simulation is not calculated anew.

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

Interacción en tiempo real

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. 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!

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Continue Physics does not work while playing the animation with AltA
Right. This works only if you start the animation with the Play button of the Timeline window.


You can than select the Soft Body object while running the simulation and Apply the modifier in the Modifiers panel of the Editing context. This makes the deformation permanent.

Consejos

  • Soft Bodies work especially well if the objects have an even vertex distribution. You need enough vertices for good collisions. You change the deformation (the stiffness) if you add more vertices in a certain region (see the animation of Image 1b).
  • The calculation of collisions may take a long time. If something is not visible, why calculate it?
  • To speed up the collision calculation it is often useful to collide with an additional, simpler, invisible, somewhat larger object (see the example to Image 1a).
  • Use Soft Bodies only where it makes sense. If you try to cover a body mesh with a tight piece of cloth and animate solely with Soft Body, you will have no success. Self collision of Soft Body hair may be activated, but that is a path that you have to wander alone. We will deal with Collisions in detail later.
  • Try and use a Lattice or a Curve Guide Soft Body instead of the object itself. This may be magnitudes faster.


Enlaces