Whiteboard VASE Plug-in Interface

Authors:

Lars Winkler Pettersson - www.handwritten.net

Magnus Andersson

Introduction

The vpiWhiteboard lets several avatars in a 3D environment interact with a shared whiteboard.

The vpiWhiteboard is a plugin designed for the Visual and Simulated Environment (VASE) and the Virtual Reality Toolkit (VRT).

The vpiWhiteboard uses the concept of vector graphics to store each drawn pen stroke as one object. Each pen stroke consists of a set of node points connected by straight lines. A document metaphor with pages is implemented so the vpiWhiteboard can be cleared without loosing its content. The vpiWhiteboard documents can be saved and restored from disk using a proprietary ASCII file format described at http://www.tugg.com/vw/vw_docs.pdf .

Using the whiteboard

Interaction with the whiteboard is carried out through mouse, digitizer tablet and keyboard input. The output is through visualization in the VASE/VRT 3D environment. The interface of both the whiteboard and the virtual room environment can be designed by changing a configuration file.

Commands in the user interface

Mouse commands are carried out using the vpiController plugins above and below the whiteboards drawing area. The top controller sets one of the five colors, white, green, blue, red or yellow as the current drawing color.

The bottom controller defines the following functions:

	Insert one page before current page
	Add one page before current page
	Delete the current page
	Clear the current page
	Move to previous page
	Move to next page
	Set eraser as active tool – The eraser removes all strokes within the rectangular area defined by the corners of a pen down and pen up on the whiteboard.
	Set pen as active tool

Mouse and digitizer tablet interaction

The command buttons on the bottom bar can only be accessed with the mouse. The digitizer tablet only supports active usage of the tool on the drawing area of the whiteboard, therefore can the digitizer tablet only be used to draw or erase pen strokes.

Note that the eraser removes all strokes within the area defined by the corners of an eraser-down event and eraser-up event on the whiteboard surface:

Keyboard interaction

F2	Opens the wtboard window.
F3	Adds a page to the whiteboard document
F4	Dialog window: open a whiteboard file stored in a proprietary ascii format.
F5	Dialog window: saves a whiteboard file stored in a proprietary ascii format.
F7	Move to previous page
F8	Move to next page

Ctrl - leftmouse button	Move the avatar into full screen viewing position. This is carried out by sending a message to the vpiAvatar plugin.

The configuration file

The VASE configuration file describes how plugins (.dll files) are positioned in the 3D environment and how they interact with other plugins

The vpiWhiteboard plugin is initiated in VASE using the component tag of the <configfile>.vas configuration file. Page interaction is handled through messages from the vpiController plugin defined below.

Example code for initiating the plugin in VASE

Comments (<!-- ) in green:

<bgcolor_r>0</bgcolor_r>

<bgcolor_g>0</bgcolor_g>

<bgcolor_b>0</bgcolor_b>

<show_pointer>0</show_pointer>

<activate_wintab>0</activate_wintab>

</component>

Example code for defining the vpiController plugin - edit

<button>wtboard:inspage

<texture>textures\ins_icon.bmp</texture>

<type>pushbutton</type>

</button>

<button>wtboard:addpage

<texture>textures\add_icon.bmp</texture>

<type>pushbutton</type>

</button>

<button>wtboard:delpage

<texture>textures\del_icon.bmp</texture>

<type>pushbutton</type>

</button>

<button>wtboard:clearpage

<texture>textures\clear_icon.bmp</texture>

<type>pushbutton</type>

</button>

<button>wtboard:previous

<texture>textures\prev_icon.bmp</texture>

<type>pushbutton</type>

</button>

<button>wtboard:next

<texture>textures\next_icon.bmp</texture>

<type>pushbutton</type>

</button>

<button>wtboard:seteraser

<texture>textures\eraser_icon.bmp</texture>

<type>radiobutton</type>

</button>

<button>wtboard:setpen

<texture>textures\pen_icon.bmp</texture>

<type>radiobutton</type>

</button>

</component>

Example code for defining the vpiController plugin - color

<!-- sends a message white to the instance of vpiWhiteboard.

Since the colors are hard coded this leaves for improvement.

-->

<button>wtboard:white

<texture>textures\white_icon.bmp</texture>

<type>radiobutton</type>

</button>

<button>wtboard:green

<texture>textures\green_icon.bmp</texture>

<type>radiobutton</type>

</button>

<button>wtboard:blue

<texture>textures\blue_icon.bmp</texture>

<type>radiobutton</type>

</button>

<button>wtboard:red

<texture>textures\red_icon.bmp</texture>

<type>radiobutton</type>

</button>

<button>wtboard:yellow

<texture>textures\yellow_icon.bmp</texture>

<type>radiobutton</type>

</button>

</component>

The whiteboard communication protocol

The whiteboard communication protocol uses the streep shared repository system to distribute drawn pen strokes from each client to all other clients. Streep guarantees that all clients will share the same data, although at some delay. The processing data unit in the communication protocol carries one stroke at a time over the network.

Processing Data Unit in the stroke distribution protocol

The processing data unit (PDU) is sent using a shared state m_pShareStroke. This shared variable takes a header STROKE_MESSAGE_HEADER and a body which is an array of WTBOARDDATANODE’s. The header describes the general properties of the stroke such as to which page it belong, what stroke color and line width it has. The number of nodes in the body of the PDU is assigned to the last value of the header. The body is an array of WTBOARDDATANODE struct’s which are describe in the documentation of the source at: http://groupnote.sf.net/vpiwhiteboard/doc/html/index.html

PDU: Header

Content	Type	Usage
Version number	unsigned char chVersion;	1
Page ID	UINT nPageID;	0 to UINT
Stroke ID	UINT nStrokeID;	0 to UINT, ids are continuously increasing during a session.
Stroke color	COLORREF StrokeColor;	R G B
Line Width	unsigned char LineWidth;	0-255 (the width is relative to users definition - the feature is currently not used in)
Length in bytes of the data segment	UINT nNodeCount;	0-65355 bytes

PDU: Body (WTBOARDDATANODE* - list of nodes)

Content	Type	Usage
X coordinate of a node	unsigned short PosX;	0-65355
X coordinate of a node	unsigned short PosY;	0-65355
Pressure	unsigned char Pressure;	0-255 127 is standard pressure stored if no pressure data is recorded.
Time stamp	unsigned long TimeStamp;	Measured in milliseconds from 1970 Jan 1, currently not used

Known problems

Problem: Using the whiteboard with the WinTab/Wacom interface blocks mouse interaction. The program window will only receive input from the WinTab/Wacom interface.

Fix1: Press Alt-Tab and choose another application. Right click on the taskbar icon for vase.exe until the taskbar menu can be viewed. When the menu can be seen the block of the windows is released.

Fix2: Set the tag activate_wintab to zero and use the wacom tablet in mouse mode.

Add the following row to the configuration file:

<activate_wintab>0</activate_wintab>

Problem: On a network with slow computers the whiteboard will occasionally loose page and stroke commands

Fix: Use fast computers in a low latency network.