Currently, the draw tool of XnView MP 0.84 beta 1 doesn't support any way of zooming; neither with the mouse wheel nor with toolbar buttons.
There should be functionality for zooming like zooming in/out, zoom to 100%, zoom fit image. (see XnView Classic)
0.84b1: Draw tool: No zooming
Moderators: XnTriq, helmut, xnview
Re: 0.84b1: Draw tool: No zooming
0.84 b2: Resolved (Zooming is possible via mouse wheel or toolbar buttons)