Smooth scrolling and button emulation

[Sascha Hlusiak]

Hi Peter,

On Donnerstag, 4. Oktober 2012 00:30:36 Peter Hutterer wrote:
> On Wed, Oct 03, 2012 at 07:17:08PM +0200, Sascha Hlusiak wrote:
> > In the case for legacy button scroll events, the server keeps track of
> > the accumulated scroll delta and after reaching 100, will generate a
> > XI1/legacy scroll button down/up sequence. Is there a way to reset that
> > server internal delta to 0 after scrolling stops? It seems that smooth
> > scrolling might leave that value at 99, which makes it impossible for
> > me to predict when the next legacy button scroll event will happen.
> 
> no, not really. this is a missing API but I do wonder how useful this API
> would be. The scroll resolution is supposed to represent one unit of
> scrolling, so it should be hard to repeatedly accumulate 99 - that would
> just mean the resolution is too high, wouldn't it?
I did notice the effect when I used it and the effect would be the same if 
resolution was set to e.g. 5. 

> > In the case of the joystick module, where deflecting the axis generates
> > a whole scroll unit, followed by smooth scrolling, this results in
> > sometimes two units from the start.
> 
> I'm not sure what you mean by "Followed by smooth scrolling". Once you
> enable smooth scrolling, you don't send button 4/5 presses anymore, only
> the valuator events. the rest is handled in the server. are you still
> setting button events as well?
I am not sending button events as well. When the axis is first deflected, I 
send out exactly one unit (value 100 in my example) to force immediate 
emulated button events. While the axis is deflected, I continue sending small 
intervals, so after some time I continually get more emulated button events, 
each time the value of 100 is reached. With button emulation I'd expect like 
1 scroll unit a second, but the first scroll unit happens at a random time, 
depending on where the counter was before. 

But when first deflecting the axis, I sometimes get two emulated button events 
right after each other.

Just a quick thought, would it be possible to use an absolute motion event 
with a value of 0 to reset the internal delta? That wouldn't break ABI. 


Cheers,
Sascha
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