This directory contains code for: rendering graphics on the canvas,
"picking" objects on the canvas based on closeness to cursor, directing
events (mouse button, key press, etc.) to the correct object.

The code can be divided into two types: handling SVG elements
(DrawingItem and derived classes) and handling controlled items
(SPCanvasItem and derived structures/classes).

Currently we rely on the "Cairo" graphics library for rendering.

DrawingItem:

  Item belonging to the drawing. These are rendered via the
  CanvasArena canvas item.

CanvasItem:

  See README in control sub-directory.

To do:

* Split into three directories: drawing, control, common (partially done).
* Rename control directory to canvas directory.
* Remove SPCurve.