Grab key scrolling

[Marco Pesenti Gritti]

On Thu, 2007-04-19 at 12:16 +0200, Bert Freudenberg wrote:
> On Apr 19, 2007, at 12:11 , Marco Pesenti Gritti wrote:
> 
> > On Thu, 2007-04-19 at 05:51 -0400, Zephaniah E. Hull wrote:
> >> On Thu, Apr 19, 2007 at 11:47:22AM +0200, Marco Pesenti Gritti wrote:
> >>> On Thu, 2007-04-19 at 01:41 -0400, Zephaniah E. Hull wrote:
> >>>> 2: This is where you have choices and tradeoffs.
> >>>>     You can simply grab the core pointer events and let the  
> >>>> pointer move
> >>>>     around, this has the problem of not being able to scroll in one
> >>>>     direction once the pointer has reached the edge of the screen.
> >>>
> >>> Yeah, this won't work.
> >>>
> >>>>     You can do a full pointer grab, as many games do, usually  
> >>>> making the
> >>>>     pointer invisible at the same time.  This allows you to scroll
> >>>>     around however you want, but without some tricks to save/ 
> >>>> restore
> >>>>     pointer position, this leaves the pointer in the middle of the
> >>>>     screen when you let go.
> >>>>
> >>>
> >>> What do you mean with full pointer grab exactly? This is what SDL  
> >>> does:
> >>>
> >>> XGrabPointer(SDL_Display, SDL_Window, True, 0,
> >>> 	     GrabModeAsync, GrabModeAsync,
> >>>              SDL_Window, None, CurrentTime);
> >>>
> >>> I tried it out with neverball and once you reach the edge you  
> >>> can't move in that
> >>> direction anymore.
> >>
> >> Extra work is needed, specificly you have to move the pointer to the
> >> center of the screen, and on each movement move the pointer back  
> >> to the
> >> center of the screen.
> >>
> >> It's ugly, but it's also how X applications have stolen the  
> >> pointer for
> >> ages.
> >>>
> >
> > OK, sounds like a reasonable approach for Gen1 to me. The only  
> > downside
> > I can think of is that we have to hide the pointer.
> 
> ... and that every activity will have to implement this.

We can provide an implementation that activities can reuse. For
GtkScrolledWindow we can provide a subclass or even patch gtk to support
this out of the box.

Clearly it would be better if it could work for everyone transparently
but I can't think of any way to do that (other that using mouse wheel
scroll events, which are fairly limited).

Marco