public void createSkidMarks(Car car) {
      SimpleVector curPos=car.getTransformedCenter();
      if (lastPos!=null) {
         SimpleVector deltaPos=curPos.calcSub(lastPos);
         float delta=deltaPos.length();
         if (delta>SKID_DELTA) {
            SimpleVector addy=deltaPos;
            addy.scalarMul(SKID_DELTA/delta);
            SimpleVector sPos=new SimpleVector(lastPos);
            while (delta>SKID_DELTA) {
               sPos.add(addy);
               skidmarks[nextMark].place(-1, car, sPos);
               skidmarks[nextMark+1].place(1, car, sPos);
               nextMark+=2;
               nextMark%=SKID_MARKS;
               delta-=SKID_DELTA;
            }
            lastPos=curPos;
         }
      }
      else {
         lastPos=curPos;
      }
   }