Optional opt_name: stringname of this as a Subject
Private dragindex of the block being dragged, or -1 when no drag is happening
Private dragthe spring dragging the block
Protected initialInitial values.
Private mouse_object that represents mouse position while dragging. Note that we don't add the mouse object to the SimList and therefore don't make a DisplayObject for it.
Static Readonly START_Constant that indicates 'start in middle' configuration.
Static Readonly START_Constant that indicates 'start on wall' configuration.
Adds the given Observer to this Subject's list of Observers, so that the Observer
will be notified of changes in this Subject. An Observer may call Subject.addObserver
during its observe method.
the Observer to add
Adds the Parameter to the list of this Subject's available Parameters.
the Parameter to add
if a Parameter with the same name already exists.
Notifies all Observers that this Subject has changed by calling observe on each Observer.
An Observer may call addObserver or removeObserver during its observe
method.
a SubjectEvent with information relating to the change
Notifies all Observers that the Parameter with the given name has changed by calling observe on each Observer.
the language-independent or English name of the Parameter that has changed
if there is no Parameter with the given name
Rebuilds the simulation from scratch with the given number of blocks, starting position, and gaps.
number of moveable blocks to make
starting position of blocks: 0 = middle, 1 = on-wall
gap between objects in starting position
Defines the differential equations of this ODESim; for an input set of variables, returns the current rate of change for each variable (the first derivative of each variable with respect to time).
The timeStep is the time since the state variables were last fully calculated, which
can be and often is zero. The current time can be regarded as getTime() + timeStep.
The input variables correspond to the Simulation state at that time. Note that
timeStep is different from the time step used to advance the Simulation (as in
AdvanceStrategy.advance).
The timeStep is typically used when finding collisions in
CollisionSim.findCollisions.
the current array of state variables (input),
corresponding to the state at getTime() + timeStep
array of change rates for each variable (output), all values are zero on entry.
the current time step (might be zero)
null if the evaluation succeeds, otherwise an object relating to the
error that occurred. The change array contains the output results.
Called at the end of a mouse drag operation, performs whatever action is
appropriate. Only called if startDrag returned true.
the SimObject being dragged, or null if no SimObject was found
the location of the mouse in
simulation coordinates of the SimView where simObject was found, or in the
focus view
if simObject is null.
distance from the initial object position to the mouse location at start of drag.
Protected getReturns whether broadcasting is enabled for this Subject. See setBroadcast.
whether broadcasting is enabled for this Subject
Returns the current EnergyInfo for this system.
an EnergyInfo object representing the current energy of this system.
Returns the ParameterBoolean with the given name.
the language-independent or English name of the ParameterBoolean
the ParameterBoolean with the given name
if there is no ParameterBoolean with the given name
Returns the ParameterNumber with the given name.
the language-independent or English name of the ParameterNumber
the ParameterNumber with the given name
if there is no ParameterNumber with the given name
Returns the ParameterString with the given name.
the language-independent or English name of the ParameterString
the ParameterString with the given name
if there is no ParameterString with the given name
Private getCalled when a key is pressed or released, performs whatever action is appropriate for that event.
the KeyboardEvent that happened
true means this is a key-down event; false means a key-up event
the modifier keys down during event
Private makeCalled at each movement during a mouse drag, performs whatever action is
appropriate. Only called if startDrag returned true.
The SimObject being moved is passed in, along with the current mouse position, in
simulation coordinates, and an offset calculated at the start of the drag.
Setting the SimObject position to (x - offsetX, y - offsetY) will move the SimObject
smoothly along with the mouse movement.
the SimObject being dragged, or null if no SimObject was found
the location of the mouse in
simulation coordinates of the SimView where simObject was found, or in the
focus view
if simObject is null.
distance from the initial object position (from DisplayObject.getPosition) to the mouse location at start of drag.
Private moveRemoves the Observer from this Subject's list of Observers. An Observer may
call removeObserver during its observe method.
the Observer to detach from list of Observers
Removes the Parameter from the list of this Subject's available Parameters.
the Parameter to remove
Sets the Simulation back to its initial conditions, see saveInitialState, and calls modifyObjects. Broadcasts event named 'RESET'.
Restores the Simulation state that was saved with saveState.
Saves the current variables and time as the initial state, so that this initial state can be restored with reset. Broadcasts event named 'INITIAL_STATE_SAVED'.
Saves the current state of the Simulation, so that we can back up to this state later on. The state is defined mainly by the set of Simulation variables, see getVarsList, but can include other data. This state is typically used for collision detection as the before collision state, see CollisionSim.findCollisions.
Protected setSets whether this Subject will broadcast events, typically used to temporarily disable broadcasting. Intended to be used in situations where a subclass overrides a method that broadcasts an event. This allows the subclass to prevent the superclass broadcasting that event, so that the subclass can broadcast the event when the method is completed.
whether this Subject should broadcast events
the previous value
Sets the Terminal object that this simulation can print data into.
the Terminal object that this simulation can print data into.
Protected setSets the VarsList for this simulation.
the VarsList to use in this simulation
Called at the start of a mouse drag. The nearest dragable SimObject is passed in,
along with mouse position in simulation coordinates. If no dragable SimObject was
found, null is passed for the first argument. If the EventHandler does not recognize
the SimObject then it should return false.
the SimObject that is nearest to the mouse drag coordinates,
or null if no SimObject was found
the location of the mouse in
simulation coordinates of the SimView where simObject was found, or in the
focus view
if simObject is null.
distance from the initial object position (from DisplayObject.getPosition) to the mouse location at start of drag
location of 'drag point' on the
SimObject in body coordinates of the SimObject; this is where for example a spring
will be attached on the SimObject when dragging; or null when no SimObject
was found
the modifier keys down during event
true if the EventHandler will handle dragging the SimObject
Returns a minimal string representation of this object, usually giving just identity information like the class name and name of the object.
For an object whose main purpose is to represent another Printable object, it is
recommended to include the result of calling toStringShort on that other object.
For example, calling toStringShort() on a DisplayShape might return something like
this:
DisplayShape{polygon:Polygon{'chain3'}}
a minimal string representation of this object.
Generated using TypeDoc
Simulation of one to three blocks moving freely in one dimension, with springs attached to the blocks, and walls on either end.
Variables
History
This was originally created to investigate collision schemes for the rigid body simulation, like serial or simultaneous collision handling. One idea for how to handle collisions is to insert springs at each collision point, and I tried a version of this in RigidBodySim. But the collisions were not behaving the way I expected. So I made this simulation to check how a simplified collision with stiff springs behaves. Indeed, this simulation shows that these spring based collisions are far from the 'ideal' collision behavior. That 'ideal' collision behavior includes things like:
if block A hits stationary block B of equal mass, then block A should be stationary, and block B is moving with same velocity.
if block A hits stationary blocks B and C (where B and C are motionless in resting contact), then block C should be the only one moving after the collision and A and B should be in resting contact.
My conclusion was that spring forces were not the right way to go for handling collisions in the rigid body simulation. However, I've learned some things from this simulation since then:
extremely short springs (short rest length) requires very high stiffness. Otherwise, the blocks just pass thru. I think it is because a spring takes some time/distance for the force to operate and if moving too fast for the length then there is not enough time/distance. You also have to use short time step.
high stiffness (60) with short times step (0.001) and a small gap (0.1) between blocks/springs somewhat satisfies the ideal collision behaviors described above. This is with low mass of 0.1, and no damping.
To Do
Add AdaptiveStepSolver to choices for DiffEqSolver; does it work better in terms of having constant energy? Otherwise, the stiff springs seem to give energy fluctuations with regular step size of 0.025; if you reduce to a very small time step of 0.0005, then the energy is fairly constant. But that's wasteful of using many tiny steps during most of the time when the springs aren't engaging.