UI Overview: 5.4 A UI Example: TicTacBoard Specifics

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The TicTacBoard object, being of a subclass of VisContentClass , handles many messages specific to content objects. However, only three messages are handled specifically by TicTacBoardClass . These messages are

MSG_VIS_DRAW
This message notifies the object it must draw itself and any accompanying graphics. TicTacBoard responds by drawing the game board (the border and crossed lines) and by passing the MSG_VIS_DRAW on to all of its children.
MSG_TICTAC_NEW_GAME
This message is sent by the New Game trigger in the Game menu. TicTacBoard responds by sending another new game message, MSG_PIECE_NEW_GAME , to each of its children. Each child will position itself and draw itself properly; TicTacBoard will then redraw the game board by sending itself a MSG_VIS_DRAW .
MSG_TICTAC_VALIDATE_BOUNDS
This message is sent by a game piece object when it is being moved. TicTacBoard checks the parameters passed and determines whether they are on the game board or not; if they are it returns TRUE, and if they aren't it returns FALSE.

Each of the methods for the above messages is shown in Methods of TicTacBoardClass . Each is heavily commented and explains the theory behind the method.

Code Display 6-5 Methods of TicTacBoardClass

/***********************************************************************
 *
 * MESSAGE:		MSG_TICTAC_NEW_GAME for TicTacBoardClass
 *
 * DESCRIPTION:		This method notifies each of the visible children that
 * 		a new game is beginning; they should take their places,
 * 		and then the board object will redraw itself
 *
 * PARAMETERS:
 * 	void ()
 *
 ***********************************************************************/
@method TicTacBoardClass, MSG_TICTAC_NEW_GAME {
    WindowHandle win;				/* the window to draw to			*/
    GStateHandle gstate;				/* the gstate of the window */
	/* First notify all the children (game pieces)
	 * that a new game is beginning.						*/
    @send @visChildren::MSG_PIECE_NEW_GAME();
	/* Now initiate a new gstate for the view window.
	 * Get the window handle from the view, and then
	 * create a new gstate for it.						*/
    win = @call TicTacView::MSG_GEN_VIEW_GET_WINDOW();
    gstate = GrCreateState(win);
	/* Invalidate the game board rectangle in the document.
	 * This will cause the view object to generate a
	 * MSG_META_EXPOSED for the rectangle, causing MSG_VIS_DRAW
	 * to be sent to this object (TicTacBoard).						*/
    GrInvalRect(gstate, 0, 0, BOARD_WIDTH, BOARD_HEIGHT);
	/* Now destroy the temporary gstate. This is important
	 * to keep too many gstate handles from being locked
	 * and slowing down the system.						*/
    GrDestroyState(gstate);
}
/***********************************************************************
 *
 * MESSAGE:		MSG_VIS_DRAW for TicTacBoardClass
 *
 * DESCRIPTION:		This method draws the board's outline and the
 *		lines of the playing field. It is sent each time
 *		a portion of the view window becomes invalid (such
 *		as when the primary is moved).
 * PARAMETERS:
 *	void (word drawFlags, GStateHandle gstate)
 *		gstate is the handle of the graphics state associated
 *		with the exposed portion of the view window
 ***********************************************************************/
@method TicTacBoardClass, MSG_VIS_DRAW {
	/* Set up the graphic state properly. The board
	 * lines are to be white and three points thick.						*/
    GrSetLineColor(gstate, CF_INDEX, C_WHITE, 0, 0);
    GrSetLineWidth(gstate, 3);
	/* Now draw the border of the game board. It is a
	 * rectangle that outlines the entire board.						*/
    GrDrawRect(gstate, 0, 0, BOARD_WIDTH, BOARD_HEIGHT);
	/* Set and draw the Tic Tac Toe playing field. The
	 * lines are now set to 4 points thickness, and the
	 * lines are drawn with HLine and VLine graphics
	 * commands. Ideally, preset constants would be used.*/
    GrSetLineWidth(gstate, 4);
    GrDrawHLine(gstate, 5, 60, 175);
    GrDrawHLine(gstate, 5, 120, 175);
    GrDrawVLine(gstate, 60, 5, 175);
    GrDrawVLine(gstate, 120, 5, 175);
	/* When the MSG_VIS_DRAW is received by the game board,
	 * it must pass it on to its visible children. It must
	 * also pass on the parameters of the message as passed
	 * to ensure all drawing is done properly.						*/
    @send @visChildren::MSG_VIS_DRAW(drawFlags, gstate);
}



/***********************************************************************
 *
 * MESSAGE:		MSG_TICTAC_VALIDATE_BOUNDS for TicTacBoardClass
 *
 * DESCRIPTION:		This method checks to see if the bounds passed
 *		are on the game board. This is invoked when a game
 *		piece is in motion and receives an END_SELECT message
 *		indicating it is being put down. The piece must
 *		determine whether the suggested bounds are on the
 *		game board; the piece should always query the board
 *		object rather than check directly; if the board were
 *		resizable, the piece could be incorrect sometimes.
 *
 * STRATEGY:		Check the four bounds against the board's edges. If
 *		all four are on the board, return TRUE. If any one
 *		of the four is off the board, return FALSE.
 * PARAMETERS:
 *	void (word bottom, word right, word top, word left)
 ***********************************************************************/
@method TicTacBoardClass, MSG_TICTAC_VALIDATE_BOUNDS {
    if (((bottom < BOARD_HEIGHT) && (top > 0))
			&& ((right < BOARD_WIDTH) && (left >= 0))) {
	return(TRUE);
    } else {
	return(FALSE);
    }
}
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