= How to make new tools =

The best is to derive from existing tools, and redefine only what you don't like.
The tools often function within a group of tools. They share a common way of using mouse buttons, and it is oke to push a tool unto the stack, and returning to the parent tool after stopping itself. Like tools based on <<Dox(a2dStTool)>> use all as controller <<Dox(a2dStToolContr)>>.

= Changing State =

A tool is used to manipulate what is in a drawing. User input combined with selected objects and mouse hit objects, brings a tool from one state into another. Down here some examples of what can bring a tool into a different state.

||<rowstyle="background-color: #FFFFE0;"> mouse event             ||key state    || object hit ||object selected|| action ||
||LeftDown                ||    || true       || 1             || Select object hit ||
||RightDown               ||    || true       || 1             || depends on drag or not ||
||LeftDown                ||Ctrl Down    || true       || 1             || deselect all & add hit object ||
||LeftDown + drag         ||Ctrl Down    || true       || 0             || deselect all & add selected objects ||
||LeftDown + drag         ||Shift Down   || true       || 0             || add selected objects in rect ||
||LeftDown + drag         ||Alt   Down   || true       || n >= 1        || move selected objects ||
||RightDown + drag        ||Ctrl  Down   || true       || 1             || drag canvas area ||
||LeftDown + LeftUp at xy ||Alt   Down   || true       || 1             || select ||
||RightDown + RightUp at xy ||Alt   Down || true       || 0             || popup menu ||
||LeftUp              ||    || true       || 1             || depending on keys, treat dragged rect ||
|| non || Space bar || false  || 0             || zoom out ||


= Tool push and pop =

A tool controller, is designed to be able to push and pop tools from a tool stack. This makes it possible to draw a polygon, and while doing push a zooming tool onto the stack, continue drawing, and zoom out again. And that way it easy to draw a polygon very accurate even it is all over the drawing. 

{{drawing:toolStateDiagram||height="501",width="775"}}

= Zoom Tool =

{{attachment:Diagram1.png}}