Autohide toolbar

Right now, when a Bokeh plot has a toolbar, the toolbar is always visible. This helps people see the tools that are available, but it is distracting when one is primarily reading through a long document, looking at several plots and not wishing to interact with any one of them.

To support this usage, I’d prefer that the default behavior is that the tools are visible only when the mouse is actually inside the plot area, and otherwise they are silently hidden (which would then also apply on export, providing a cleaner exported figure). Presumably the tools could be set to be invisible (alpha=0) whenever the mouse is outside the plot area?

An implementation of this would be to add an option autohide to Toolbar, and once supported we could debate whether it should be True or False by default.

[bryevdv]

@mattpap the example upon which this is based, simply hides the toolbar without altering the layout. That is expressly all that is wanted or being asked for. The toolbar does not need to be in the center layout, it just needs to allocate space as if it were going to draw, but then not actually draw (unless the cursor is inside w hit region).

For that matter, we could even flip things: we could have a div on top of the toolbar that fades to and from transparent (instead of having the toolbar itself fade to and from opaque)

[jsignell]

@mattpap, are you worried about how the tool bar should show up when the mouse is over the plot? Is it hard for an event from the center layout to have an effect in the toolbar?