Extérieur¶
Les forces extérieures sont appliquées aux sommets (et presque exclusivement aux sommets) d’objets Soft Body. Ceci est fait en utilisant les Lois de la physique de Newton.
- Si il n’y a aucune force sur un sommet, il demeure immobile ou se déplace avec une vitesse constante en ligne droite.
- L’accélération d’un sommet dépend de sa masse et de la force. Plus la masse est grande, plus l’accélération est faible. Plus la force est grande, plus l’accération est grande.
- Pour chaque action il y a une réaction égale et opposée.
Well, this is done only in the range of computing accurateness, there is always a little damping to avoid overshoot of the calculation.
Exemple¶
Nous allons commencer avec un exemple très simple : le cube pae défaut.
- Pour juger l’effet des forces externes, vous devriez d’abord désactiver Goal, de sorte que les sommets ne sont pas rétractés sur leur position d’origine.
- Press Alt-A to run the simulation.
Que se passe-t-il ? Le cube se déplace dans le direction Z négative. Chacun des huit sommets est affecté par une force constante globale – la gravité. La gravité sans friction est indépendant du poids d’un objet, ainsi tout objet que vous utiliseriez comme Soft body ici tombera avec la même accélération. L’objet ne se dlforme pas, parce que tous les sommets se déplacent avec la même vitesse dans la même direction.
Champs de force¶
Soft body vertices interact with all the Force Fields applied (usually to particles) in the layer, such as wind, force fields, and what ever physics field effect is on a common layer.
Soft Body Field Weights¶
Référence
| Panneau: |
|---|
The Soft Body Field Weights panel allows you to control how much influence each type of external force field, has on the soft body system.
- Effector Group
- Limit effectors to a specified group. Only effectors in this group will have an effect on the current system.
- Gravity
- Control how much the Global Gravity has an effect on the system.
- All
- Scale all of the effector weights.
Aérodynamique¶
Edges can be affected by wind as they move, and sail or flutter in a breeze. A simple aerodynamic model of a flag sailing in the wind.
Cette force externe spéciale n’est pas appliquée aux sommets mais aux arêtes connectées. techniquement, une force perpendulaire à l’arête est appliquée. La force avec laprojection de la vitesse relative sur l’arête (produit scalaire). Notez que la force est la même si le Vent (win) souffle ou vous tirez l’arête dans l’air avec la même vitesse. Cela signifie qu’une arête en mouvement dans sa propre direction ne subit aucune force, et une arête se déplaçant perpendiculairement à sa propre direction subit une force maximale.
The angle and the relative speed between medium and edge is used to calculate the force on the edge. This force results that vertices with few connecting edges (front of a plane) fall faster than vertices with more connecting edges (middle of a plane). If all vertices have the same amount of edges in a direction they fall with equal speed.
The Aerodynamics settings are set in the Soft Body Edges panel.
Goal¶
A « goal » is a shape that a soft body object tries to conform to. It acts like a pin on a chosen set of vertices, controlling how much of an effect soft body has on them.
Enabling Soft Body Goal tells Blender to use the position (or animated position) of a vertex in the simulation. Animating the vertices can be done in all the usual ways (F-curves, armatures, parents, lattices, etc.) before the soft body simulation is applied. The « goal » is the desired end position for vertices. How a soft body tries to achieve this goal can be defined using stiffness forces and damping.
See the Soft Body Goal settings for details.
Goal Strength¶
The Goal Strength defines how much motion from an animation system gets applied.
A Goal value of 1.0 means no soft body simulation, the object act like any regular animated object, (the vertex keeps at its original position). When setting Goal to 0.0 (or no goal), the vertex is only influenced by physical laws according to soft body simulation.
By setting goal values between 0.0 and 1.0, you can blend between having the object affected only by the animation system, and having the object affected only by the soft body effect.
Goal also serves as a memory, to make sure soft objects don’t deform too much, ending up in the non-soft animated shape. Using the Vertex Group weight system, you can define a Goal weight per vertex. To make this look more natural, spring forces can be defined to control how far vertices can move from their original position.
Often Peinture de poids is used to adjust the weight comfortably. For non-mesh objects the Weight parameter of their vertices/control points is used instead; Specials menu W in Edit Mode or use the Transform panel in the Properties region. The weight of Hair particles can also be painted in Particle Edit Mode.
Technical Details¶
In the Soft Body world vertices of meshes are treated as particles having a mass. Their movement is determined by the forces affecting them. Beside other forces the individual particles can interact with another along edges using a physical model which is very close to shock absorbers used in cars. The working parts are:
- A spring trying to keep the particles at a certain distance. How hard the spring tries to do that is controlled by the soft body parameter Stiffness.
- A damping element to calm the movement down. The resistance the element builds up against motion is controlled by the soft body parameter Damping.