Grab key scrolling

Bert Freudenberg bert at
Thu Apr 19 06:16:14 EDT 2007

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.

- Bert -

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