Re: Scrolling a Cairo drawing-area or Gtk layout

[Damien Caliste <damien caliste cea fr>]

Hello,

Le 21/07/2015, Roger Matthews <roger matthews hotmail com> a écrit :
> which results from a simple straight line equation, and*/ /* that
> extends beyond the bounds of the window.
Reading your code quickly, it seems to me that, you're drawing indeed
the line outside the drawing area, *but* the drawing area has the size
of your window, so GTK is not displaying any scrollbars.

In my opinion, you should :
- in main, declare your drawing area to a fixed size (let say
  1200×1200) and declare your window size at 600×400 as you're doing ;
- in the drawing method (do_drawing()), don't use the window size, but
  the drawing size as bounds from your drwaing commands. It's useless
  to draw lines or whatever outside the cairo drawing area, they will
  be cropped anyway. So don't reach for the top level there, use the
  size of the widget itself.

As a schemme :
- your implementation : |#####|
- the way to do it : |----######----------------|
  - # means GTK scrollview, - means drawing area
  - call cairo drawing primitives in the coordinates of the drawing area
    (-), but not outside.

Damien.