public override void ShowTooltipWindow (TextEditor editor, Control tipWindow, TooltipItem item, Gdk.ModifierType modifierState, int mouseX, int mouseY)
{
var location = editor.OffsetToLocation (item.Offset);
var point = editor.LocationToPoint (location);
int lineHeight = (int) editor.LineHeight;
int y = (int)point.Y;
// find the top of the line that the mouse is hovering over
while (y + lineHeight < mouseY)
y += lineHeight;
var caret = new Gdk.Rectangle (mouseX, y, 1, lineHeight);
tooltip = (DebugValueWindow)tipWindow;
tooltip.ShowPopup (editor, caret, PopupPosition.TopLeft);
}