Visual C# [NULL]'ya da bir Odak dörtgenini Lastik bant dikdörtgen çizmek için

Boolean bHaveMouse;
Point	ptOriginal = new Point();
Point	ptLast = new Point();

// Called when the left mouse button is pressed. 
public void MyMouseDown( Object sender, MouseEventArgs e )
{
	// Make a note that we "have the mouse".
	bHaveMouse = true;
	// Store the "starting point" for this rubber-band rectangle.
	ptOriginal.X = e.X;
	ptOriginal.Y = e.Y;
	// Special value lets us know that no previous
	// rectangle needs to be erased.
	ptLast.X = -1;
	ptLast.Y = -1;
}
// Convert and normalize the points and draw the reversible frame.
private void MyDrawReversibleRectangle( Point p1, Point p2 )
{
	Rectangle rc = new Rectangle();

	// Convert the points to screen coordinates.
	p1 = PointToScreen( p1 );
	p2 = PointToScreen( p2 );
	// Normalize the rectangle.
	if( p1.X < p2.X )
	{
		rc.X = p1.X;
		rc.Width = p2.X - p1.X;
	}
	else
	{
		rc.X = p2.X;
		rc.Width = p1.X - p2.X;
	}
	if( p1.Y < p2.Y )
	{
		rc.Y = p1.Y;
		rc.Height = p2.Y - p1.Y;
	}
	else
	{
		rc.Y = p2.Y;
		rc.Height = p1.Y - p2.Y;
	}
	// Draw the reversible frame.
	ControlPaint.DrawReversibleFrame( rc, 
					Color.Red, FrameStyle.Dashed );
}
// Called when the left mouse button is released.
public void MyMouseUp( Object sender, MouseEventArgs e )
{
	// Set internal flag to know we no longer "have the mouse".
	bHaveMouse = false;
	// If we have drawn previously, draw again in that spot
	// to remove the lines.
	if( ptLast.X != -1 )
	{
		Point ptCurrent = new Point( e.X, e.Y );
		MyDrawReversibleRectangle( ptOriginal, ptLast );
	}
	// Set flags to know that there is no "previous" line to reverse.
	ptLast.X = -1;
	ptLast.Y = -1;
	ptOriginal.X = -1;
	ptOriginal.Y = -1;
}
// Called when the mouse is moved.
public void MyMouseMove( Object sender, MouseEventArgs e )
{
	Point ptCurrent = new Point( e.X, e.Y );
	// If we "have the mouse", then we draw our lines.
	if( bHaveMouse )
	{
		// If we have drawn previously, draw again in
		// that spot to remove the lines.
		if( ptLast.X != -1 )
		{
			MyDrawReversibleRectangle( ptOriginal, ptLast );
		}
		// Update last point.
		ptLast = ptCurrent;
		// Draw new lines.
		MyDrawReversibleRectangle( ptOriginal, ptCurrent );
	}
}
// Set up delegates for mouse events.
protected override void OnLoad(System.EventArgs e)
{
	MouseDown += new MouseEventHandler( MyMouseDown );
	MouseUp += new MouseEventHandler( MyMouseUp );
	MouseMove += new MouseEventHandler( MyMouseMove );
	bHaveMouse = false;
}