Tutor.com Classroom How-To #8: trapping and processing mouse movement in an InkPresenter

These How-To tips are taken from The Tutor.com Classroom: Architecture and techniques using Silverlight, WPF, and the Microsoft .NET Framework.

You can check out the Silverlight Tutor.com Classroom in "practice" mode, although the real experience is with a live tutor on the other side!

In the MouseDown event, instantiate a module-level Stroke object (e.g. m_DrawingStroke) to collect points traversed by the mouse. Fire the StrokeAdded event so that listeners can prepare for the operation as necessary. Most importantly, call CaptureMouse() to notify the mouse input engine to give you high frequency mouse event notifications.

void Whiteboard_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
  //get our current position
  Point p = e.GetPosition(this);

  //create a new styluspoint collection for our new stroke
  StylusPointCollection coll = new StylusPointCollection();
  coll.Add(new StylusPoint() { X = p.X, Y = p.Y });

  m_DrawingStroke = new Stroke(coll);

  //fire notification event
  if (this.StrokeAdded != null)
    this.StrokeAdded(m_DrawingStroke);

  //begin capturing mouse input
  this.CaptureMouse();
}

In MouseMove, add the traversed point to the Stroke’s StylusPoints collection, and fire the StrokeChanging event to alert interested listeners.

void Whiteboard_MouseMove(object sender, MouseEventArgs e)
{
  //get our current position
  Point p = e.GetPosition(this);

  //add the traversed point to our collection
  StylusPoint sp = new StylusPoint() { X = p.X, Y = p.Y };
  m_DrawingStroke.StylusPoints.Add(sp);

  //fire notification event
  if (this.StrokeChanging != null)
    this.StrokeChanging(m_DrawingStroke);
}

In MouseUp, release mouse capture and fire the StrokeComplete event.

void Whiteboard_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
  //release mouse capture
  this.ReleaseMouseCapture();

  //fire notification event
  if (this.StrokeComplete != null)
    this.StrokeComplete(m_DrawingStroke);
}