Re: [Linuxwacom-discuss] Pressure curve and click threshold interaction

[Jason G. <kil...@gm...>]

On Wed, Feb 9, 2011 at 9:00 PM, Chris Bagwell <ch...@cn...> wrote:
> On Wed, Feb 9, 2011 at 2:16 AM, Jason Gerecke <kil...@gm...> wrote:
>> On Tue, Feb 8, 2011 at 9:06 PM, Chris Bagwell <ch...@cn...> wrote:
>>>
>>> I just tried this with Gimp.
>>>
>>> * With default Threshold of 27 and default PressureCurve I can draw
>>> very light marks.
>>> * With Threshold set to 1024 I can only draw lines that start with
>>> medium darkness starting when I apply medium pressure.
>>> * With Threshold set to 2000 I can only draw very dark lines by
>>> applying (overly) firm pressure.
>>>
>>> So although the pre-Threshold pressure values are reported, at least
>>> this application ignores reported pressure until Threshold is
>>> reached/button is clicked.  I assume that's how all apps work as well.
>>>
>>
>> I've tested a handful more pressure-sensitive apps (Inkscape, Xournal,
>> JTablet) and all are acting in the same way. Strokes begin/end with
>> button down/up events.
>>
>>> To decide best option, I still need to get a better feel for what
>>> Threshold is meant to do or how mainly used.  I know it limits button
>>> generation but why is that useful?
>>>
>>> Its just an easy way to make just the initial touch feel firmer/harder
>>> without resorting to pressure curves, right?  One could use
>>> PressureCurve to map HW pressure of 27 to 0 and get same affect
>>> without Threshold option, right?
>>>
>>
>> Setting a threshold like that with the PressureCurve setting alone is
>> not possible. The bezier curve defined by it has four control points,
>> two of which are fixed at (0,0) and (1,1). To map greater-than-minimum
>> HW pressure to zero, you'd need to change the first fixed point. To
>> achieve an effect like the Polycount thread suggests with
>> less-than-maximum HW pressure producing maximum pressure you'd need to
>> change the second fixed point.
>>
>> I'm not sure we'd want to make a change like that, but it would be
>> possible to maintain a click threshold separately from a pressure
>> threshold with such a change.
>
> I agree we can not remap HW pressures to zero using todays [0..100]
> limits for points.  I'm thinking we should probably update
> xf86-input-wacom to allow greater ranges (say [-50..150]) instead of
> allowing to modify fixed points.
>
Modifying fixed points would be a lot easier to comprehend IMO. For
instance, if I wanted to slightly nudge the threshold up, I'd move the
first fixed point from (0,0) to (5,0) and the first control point to
(5,0) as well. If that weren't enough, I may change them to (10,0). In
the same situation, its a lot harder to figure out what you need to
change to have the same effect in your scheme.

As an added benefit of being able to move fixed points, you gain the
ability to make some pretty interesting pressure curves (not that most
apps even need that ability). I hacked in the ability to modify the
fixed points earlier today and gave it a whirl, and there are a number
of interesting effects to be had. My favorite curve has the feel of a
soft nib up to a point, after which it quickly starts to "run dry".
For the bezier.html you posted, my points would be roughly (0,0)
(80,0) (70,100) (100,0).

All this is getting off topic though... I think we should probably
break this out into another discussion (its late here though, so I'm
gonna be lazy and not do it myself :D)

Jason