GettingStarted: How to start using Formula Editor library with *GWT* and *Java SE*.

[Bulat Sirazetdinov]

GettingStarted: How to start using Formula Editor library with *GWT*
and *Java SE*.

All API and class hierarchies are subject to change !
Please, provide your ideas of better API. :)

There is an *example* of an editor built over this library:
Example.java (in org.formed.client.example package). You can get
started by looking at it, playing with it and building your own
version.

= GWT =

If you want to use another *Canvas* implementation than we do, then
follow the *Java SE* section instructions.

= Java SE =

If you want to use this library within Java SE application you'll have
to:

a) derive a new descendant from a BaseDrawer class. Just look at
SurfaceDrawer class and do the same. There's not much work to be done
- you have to provide line drawing, text measuring and rendering
routines, etc.

b) re-write Example.java to use your Drawer implementation instead
of SurfaceDrawer, and to use the UI-rendering and event handling of
the *Java SE* GUI framework that you are using.

= Architecture =

Formulas (equations) are constructed with Formula objects and
FormulaItem implementations: SimpleElement, OperatorElement,
LeftCloser, RightCloser, DivisorElement, FunctionElement, RootElement.
Just have a look at the top of Example.java code. You might need other
classes from org.formed.client.formula.elements package (BaseElement,
PoweredElement, PlaceElement) if you want to add your own types of
items (elements).

Editing capabilities are coded:
* mostly in BaseDrawer abstract class where only platform
independent code is present (SurfaceDrawer is derived from it and adds
actual rendering of primitives). If you want, you can code completely
different Drawer implementation.
* the other part is in Example.java.

Platform specific rendering code is isolated in SurfaceDrawer class
that is derived from BaseDrawer abstract class (where only platform
independent code is present).

Cursor class is used to specify the place where the cursor is
positioned in a formula. You have to tackle with it only if you are
redoing editor internals - BaseDrawer etc. (but in that case you'll
have it a lot).

Undo/redo: we use Command pattern for this. All commands are provided
to Undoer by the Drawer that you use. But the origin of them is
different:
* some commands are constructed by FormulaItem implementations
* and some are by BaseDrawer implementation of Drawer.