gistfile1.txt

PROCEDURE Move * (VAR p:Base; dt:Float; VAR r:Reflection; mode:MovementMode): BOOLEAN;
  (** Moves the specified particle p in all the space with a straight trajectory
      taking into account possible reflections from walls. r.Process(p) is
      called every time after the particle is collided with the wall and
      mirror-reflected form it. At that p.r contains coordinate of the collision
      with the wall, p.v contains speed of the particle after the elastic mirror
      reflection, r.wall contains the wall, r.alive contains TRUE.
      If r.alive=FALSE after the collision then the particle is not anymore
      moved. Also r.Process() may change p.v.

      There are 2 possible modes of motion specified by mode:
      1) mode = InTime. In this case the particle is moved until the specified
      time dt is passed.
      2) mode = InSpace. In this case the particle passes the distance which is
      equal to initial particle speed multiplied by dt. In this mode r.Process()
      may not set p.v to zero.
      The modes are different only is the collision with walls takes place and
      the particle speed is changed by r.Process().

      The procedure returns if the movement was valid. *)
  VAR
    NextR,n:Vector;
    w:Wall.Wall;
    alive:BOOLEAN;
    counter:INTEGER;
    dr,AbsV,PassedDistance:Float;
    d:CollData;
  BEGIN
    ASSERT(dt>0);
    AbsV:=Vec.Abs(p.v);
    ClearCollData(d);
    counter:=0;
    PassedDistance:=0;
    REPEAT
      GetNextPos(p,dt,NextR,w,d);
      IF (w#NIL) & (dt#0) THEN (* The 2nd condition may take place owing to rounding errors *)
        (* Now NextR contains the cross of the trajectory with w *)
        ASSERT(dt>0);
        dr:=AbsV*dt; (* Rest dr *)
        p.r:=NextR;
        w.Normal(NextR.x,NextR.y,n);
        ReflectSpeed(p,n);
        r.alive:=TRUE;
        r.wall:=w;
        PassedDistance:=PassedDistance+Vec.Dist(p.r,NextR);
        r.PassedDistance:=PassedDistance;
        r.Process(p);
        alive:=r.alive;
        IF alive THEN
          IF mode=inSpace THEN
            AbsV:=Vec.Abs(p.v);
            ASSERT(AbsV#0);
            dt:=dr/AbsV;
            ASSERT(dt>0);
          END;
        END;
        INC(counter);
      ELSE
        p.r:=NextR;
        dt:=0;
        alive:=TRUE;
      END;
    UNTIL (dt<=0) OR ~alive OR (counter>=MaxReflectionCount);
    RETURN counter<MaxReflectionCount
  END Move;