When a mouse click occurs on the canvas of a plot, how is the mouse button state, key state, and position of that click queried?

I have plot with a canvas, that has a single point Picker. I've connect the Pickers selected signal to a slot in my class. The problem is, the slot is only called in response to unmodified left clicks. What I want is to be able to respond to any mouse click, with any modifier -- and my slot code with query the mouse button state and key state to determine what to do.

Is this possible? If so, how?

I've scoured the examples that come with Qwt, but none of them seems to have logic that does what I want.