Comment 22 for bug 790130

Investigating the missing "pressure" when palette changes.
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Looking into the source code, the relevant files seem to be as follows:

./ui/dialog/swatches.cpp - swatch changes
./widgets/toolbox.cpp - usepressure (see "Use the pressure of the input device")
./dyna-draw-context.cpp - (see "Influence of pressure on thickness")

Using gdb to attach to the inkscape process, and putting a breakpoint on
dyna-draw-context.cpp at the line 437 just after the line where the pressure
value is determined
  double pressure_thick = (dc->usepressure ? dc->pressure : 1.0);
we see that normally (e.g. when using the "Auto" palette), the values are OK:

Breakpoint 1, sp_dyna_draw_brush (event_context=0x3fbc120, event=0x3ce61c0)
    at ../../inkscape/src/dyna-draw-context.cpp:438
438 Geom::Point brush_w = SP_EVENT_CONTEXT(dc)->desktop->d2w(brush);
(gdb) print pressure_thick
$3 = 0.10400390625
(gdb) cont
Continuing.

But after switching to the "Inkscape default" palette and back again
to the "Auto" palette, the pressure_thick is "stuck" at 1 all the time,
because even though dc->usepressure is TRUE, the dc->pressure value
is "stuck" at 1. Why?

Breakpoint 1, sp_dyna_draw_brush (event_context=0x3fbc120, event=0x41c5b40)
    at ../../inkscape/src/dyna-draw-context.cpp:438
438 Geom::Point brush_w = SP_EVENT_CONTEXT(dc)->desktop->d2w(brush);
(gdb) print pressure_thick
$17 = 1
(gdb) cont
Continuing.