void GUI_TOUCH_Exec(void) {
  #ifndef WIN32
  static U8 ReadState;
  int x,y;
  /* calculate Min / Max values */
  if (xyMinMax[GUI_COORD_X].Min < xyMinMax[GUI_COORD_X].Max) {
    xMin = xyMinMax[GUI_COORD_X].Min;
    xMax = xyMinMax[GUI_COORD_X].Max;
  } else {
    xMax = xyMinMax[GUI_COORD_X].Min;
    xMin = xyMinMax[GUI_COORD_X].Max;
  }
  if (xyMinMax[GUI_COORD_Y].Min < xyMinMax[GUI_COORD_Y].Max) {
    yMin = xyMinMax[GUI_COORD_Y].Min;
    yMax = xyMinMax[GUI_COORD_Y].Max;
  } else {
    yMax = xyMinMax[GUI_COORD_Y].Min;
    yMin = xyMinMax[GUI_COORD_Y].Max;
  }
  /* Execute the state machine which reads the touch */
  switch (ReadState) {
  case 0:
    yPhys = TOUCH_X_MeasureY();
    TOUCH_X_ActivateY();  /* Prepare X- measurement */
    ReadState++;
    break;
  default:
    xPhys = TOUCH_X_MeasureX();
    TOUCH_X_ActivateX();  /* Prepare Y- measurement */
    /* Convert values into logical values */
    #if !GUI_TOUCH_SWAP_XY   /* Is X/Y swapped ? */
      x = xPhys;
      y = yPhys;
    #else
      x = yPhys;
      y = xPhys;
    #endif
    if ((x < xMin) || (x > xMax)  || (y < yMin) || (y > yMax)) {
      _StoreUnstable(-1, -1);
    } else {
      x = _AD2X(x);
      y = _AD2Y(y);
      _StoreUnstable(x, y);
    }
    /* Reset state machine */
    ReadState = 0;
    break;
  }
  #endif /* WIN32 */
}
void GUI_TOUCH_X_ActivateX(void) {
}

void GUI_TOUCH_X_ActivateY(void) {
}
请哪位高手帮我把GUI_TOUCH_Exec(void)这个程序解释下，特别是ReadState变量的作用。例外GUI_TOUCH_X_ActivateX(void)，GUI_TOUCH_X_ActivateY(void)两个函数在移植时是空的，我该如何编写其定义程序，谢谢。有这方面好的资料推荐下，我愿意花钱买。