15.3.636  src/lib/x-kit/tut/nbody/gravity-simulator.api

## gravity-simulator.api
#
# Define interface to our (primitive) physics engine.
# This runs a thread regularly updating the positions
# of the planets according to n-body gravitational interactions.

# Compiled by:
#     src/lib/x-kit/tut/nbody/nbody-app.lib

# This api is implemented in:
#     src/lib/x-kit/tut/nbody/gravity-simulator.pkg

stipulate
    include package   threadkit;                                        # threadkit     is from   src/lib/src/lib/thread-kit/src/core-thread-kit/threadkit.pkg
herein

    api Gravity_Simulator {

        package v:  api {
                        Vector = (Float, Float);                        # Was abstract, had to make concrete to get nbody.pkg to compile. -- 2009-12-10 CrT
                        proj2d: Vector -> { x: Float, y: Float };
                    };

        Vector = v::Vector;

        Planet(X)
            =
            {   position:  Vector,                                      # 2-D Float position.
                velocity:  Vector,                                      # 2-D Float velocity.
                mass:      Float,                                       # Mass in grams.
                user_data: X                                            # Arbitrary user data associated with planet.
            };

        Plea_Mail(X)
          = SET_SIMSECS_PER_SIMSTEP     Float                           # Seconds of simulation time per gravity simulation step.
          | SET_SIMSTEPS_PER_50MS       Int                             # Number of orbiting bodies.
          | ADD_PLANET                  Planet(X)                       # New orbiting body.
          | GET_PLANETS                 Mailslot( List( Planet(X) ))    # Return list of currently orbiting planets.
          | STOP
          ;

        start:
          { g:                          Float,                          # Gravitational constant in CGS ("centimeter-gram-seconds") system (6.67428e-8)
            planets:                    List( Planet(X) ),              # List of orbiting bodies.
            #
            simsecs_per_simstep:        Float,                          # Seconds of simulation time per gravitational simulation step.
            simsteps_per_50ms:          Int,                            # Set relationship between simulation time and real wallclock time.
            plea_slot:                  Mailslot(  Plea_Mail(X) )
          }
          ->
          Microthread;
    };

end;