Re: porting gdk -> cairo

[Allin Cottrell <cottrell wfu edu>]

On Wed, 11 Aug 2010 jcupitt gmail com wrote:

> On 11 August 2010 02:14, Allin Cottrell <cottrell wfu edu> wrote:
> > rid of GdkGC.  I'd imagine that the effect I'm after is something
> > that many GTP apps have need of, and it's trivial to achieve with
> > the GDK API.
>
> I've found that XOR rubber banding is quite hard to do reliably in
> gdk.  The problem I think is that you are using the screen pixels to
> store part of the state, and that gets hard to coordinate between the
> various things that can affect the display.
>
> I had mouse movements triggering rect moves, mouse moves with a button
> held down causing background scrolling of the canvas, and mouse moves
> over other screen objects triggering highlight effects. With all these
> things going on at once it became very difficult to get XOR rubber
> bands to not leave annoying trails as they moved.
>
> I switched to an update-model / invalidate-widget / redraw-on-idle
> scheme as Dov suggests and I got prettier updates with less
> complication. Since input and output are decoupled, it'll scale more
> gracefully between slower and faster machines as well, which is nice.

My drawing case may be simpler than yours -- there's nothing
scrollable in the vicinity -- but I've found that rubber-banding
using GDK_INVERT to "undraw" the last box works flawlessly at
low programming cost.

But can you suggest a good example to look at for the alternative
approach? Thanks.

Allin Cottrell