Add a tool to expand, collapse, and select variables in the N2 diagram

[tadkollar]

Summary of Issue

Add a button or buttons to the toolbar to expand, collapse, and select variables in the N2 diagram.

Issue Type

• Bug
• Enhancement
  POEM # N/A

Description

The existing method to expand/collapse nodes in the N2 is to right-click, and alt-right-click to select variables. This is described in the Help window but is not particularly obvious. Also, right-click in Firefox by default will pop up a browser menu in addition to performing the action.

Add a toolbar button that toggles a mode in the N2 diagram where the only functionality is expanding or collapsing nodes by left-clicking on them. An obvious method should be available to open the variable selection dialog as well - maybe in the expand/collapse mode, components have a clickable button appear on them, e.g. [+].