Babelsberg/JS

A LivelyKernel implementation of Babelsberg licensed under MIT

See also Babelsberg/R

It allows you to do stuff like this

z3 = new ServerZ3()
z3.reset()
a = lively.morphic.Morph.makeRectangle(0, 0, 10, 10)
b = lively.morphic.Morph.makeCircle(pt(0,0), 10)
always: {
    solver: z3
    a.getPosition().dist(b.getPosition()) == 200
}
a.getPosition() // lively.pt(0.5,-200.0)
b.getPosition() // lively.pt(0.0,0.0)

a.setPosition(pt(100, 100))
a.getPosition() // lively.pt(100.0,100.0)
b.getPosition() // lively.pt(99.9,300.0)

Basically, you can write constraints using the always primitive that you always want to be true, using existing object-oriented abstractions (I am using the methods getPosition and dist in the example above), and the system will maintain them. The extent to which the system is able to keep constraints satisfied depends on the solver that is used. This implementation provides Z3, DeltaBlue, and Cassowary.

We have used this to implement electrical simulations, a simulation of the Lively Engine, and some graphical layouting examples. The implementation is available to try at lively-web.org. At any given time it may be broken, though, because the code is changing fairly often.

Papers about this implementation are forthcoming and a freely accessible technical report will be published shortly.

Created under a grant from Hasso Plattner Institute