Into a Physics Simulator

Hi, this is my first post in PlanetKDE 🙂 . In this post I will be talking about the new features that I am trying to implement
in the KDE Physics Simualator STEP.
First one is the ‘FRAME-CHANGE’ feature. With this feature STEP will be able to give the users a better feel
of relative motion between the bodies. After enabling frame-change the user can select a body and STEP will observe the motion
of all the bodies on the scene relative to the currently selected body. STEP will be able to show that the path of one projectile
as seen from another projectile is a straight-line ( given the value of acceleration-due-to-gravity is same for both ).

I implemented it using the void QGraphicsView::centerOn(qreal x, qreal y)  method. Since the view is to be fixed to the body
which is currently selected, I take the currentIndex() from the ItemSelectionModel and then pass the co-ordinates of thus obtained
QGraphicsItem  to the QGraphicsView::centerOn(qreal x, qreal y) method.

Next one is the ‘REWIND’ feature. Watching the simulation go forward in time was becoming a littel boring 🙂 . Bring in something new
…. STEP will now have a REWIND button just beside the Simulate button. If the rewind button is pressed while the simulation is
 going on, world->time  begins to decrease and the worldscene travels back in time.

Implementation is quite simple. Integration with a +(ve) timescale gives forward simulation. Change the timescale to -(ve)  and you get
the REWIND feature (Or alternatively we can reverse the velocities of all the bodies ). Adjustments are needed to accomodate collisions
while rewinding. It works fine for simple scenes, but there are issues when using different values of restitution-coefficients and  in
cases where friction is there.

Another feature I am trying to do is the Pulley Joint. STEP already has Anchor, Pin, and Stick Joints. It will be a simple disc with
two handler items ( which can snap to a rigid-body or a particle ). The ration of the Pulley will be fixed and equal to one. Yes,
a very simple pulley. The constraint-eqations of the pulley-joint are causing some serious head-ache at the moment.
The same little problem is there in getting the equations and values correct in case of friction.
I hope to fix it soon….


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