This required creating a simple framework for operations to LdCanvas.
It is probable that it's going to require some changes when other
operations are added. The basic idea behind it seems to be good, though.
* Rename ld_canvas_translate_*_coordinates() to ld_canvas_*_to_*_coords().
* Add missing parameter assertions to those functions.
* Rename local variables in draw_grid().
* Use gdk_cairo_rectangle() in expose-event handler.
* Update comments.
1. Add methods for coordinate translation between cairo/GtkWidget
coordinates and LdDocument coordinates.
2. Draw the grid correctly (also make it significantly faster).
3. Place the canvas into a GtkScrolledWindow and register
the set_scroll_adjustments signal in the GtkWidget base class.
4. Allow scrolling inside of an area of 200 x 200 units (for now).
In the future, it should be possible to go to infinity.
Přemysl Eric Janouch