Re: [Tuxpaint-devel] Started the port to SDL3

[Bill K. <nb...@so...>]

On Tue, Jul 15, 2025 at 01:53:49AM +0200, Pere Pujal i Carabantes wrote:
> El dc. 02 de 07 de 2025 a les 10:37 +0200, en/na Pere Pujal i Carabantes va escriure:
> > I've see them, thanks.
> > 
> > Now I am slowly porting the magic tools, one by one.
> 
> Magic tools have been ported, I am currently adding PEN pressure support to tuxpaint.c
> 
> Pressure draw with the main tip of the pen seems to work, both brush size and brush opacity,
> can be enabled/disabled with CTRL T for transparency and CTRL W for width.
> There are some values that may/should? be made available in tuxpaint-config 
> but for now they are set to what works in my system.

In this case, by "width" you mean "spacing", correct?
There's a feature I'd like to add that allows brush sizes
to be altered via the UI as well.  I feel as though that
forthcoming feature would be better served by pressure
sensitivity, than the spacing feature.  (I admit, I don't
actually do much art myself, and rarely with a tablet.
It just 'feels' like pressure changing spacing would be
confusing.)

For now, until we can add the brush sizing feature
(or perhaps forever?), I think transparency makes the most
sense.

And I would definitely want the ability to disable it for
users who are not yet familiar/comfortable with pressure
(i.e., an option to ignore pressure, and always be 100% opaque).

Reporting pressure to Magic Tools probably makes sense, but
I really need to sit down and think how & when, and how things
should behave when pressure is unavailable.

Obviously, right now -- for the past 23 years -- pressure has NOT
been available.  However, once we start adding pressure sensitivity
to existing tools, and adidng new tools that support it, we'll want
them all to behave intuitively and sensibly when the input lacks
pressure (i.e., a regular mouse, a joystick, the keyboard, or a
tablet with pressure disabled).


> Still need to decide what to do when the user switches tips to the secondary one, 
> maybe hardcode it to the eraser tool?

This is what I've always imagined. :)
See ancient ticket https://sourceforge.net/p/tuxpaint/feature-requests/8/

I imagine it could just behave like Tux Paint does when holding
the [X] key.  From README:

  Hold the [X] key while clicking for quick access to a small sharp round
  eraser (not available when the Text or Label tools are selected, when
  you're in the process of rotating a stamp or shape, or when using an
  interactive magic tool). Release the mouse to return to your
  currently-selected tool.

Of course, if pressure is enabled, then we'd want the eraser
to behave differently depending on the pressure.

Right now, Erasers are basically just hard-coded shapes (the old
"whiteboard eraser" square, then more recently circles, fuzzy
circles, and transparent circles).  While somewhat limiting in
many ways, this also means we can just go in and code things how
we want, for this special stylus version of the [X]-key-held
eraser.


> I use an old Wacom graphire to test, but the pen is very used, I already had to solder it to get it working again.
> If somebody has a spare graphics tablet that can send my way I will be very grateful :)

I've asked Pere how I can help here. :-)

-bill!