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Implement stylus pressure curve support

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Takes a 4-point cubic bezier curve as input and maps the pressure coordinates
to the values outlined by this curve. This is an extension of the current
implementation in the xf86-input-wacom driver which only allows the two center
control points to be modified.

Over the years a few users have noted that the wacom driver's pressure curve
makes it impossible to cap the pressure at a given value. Given our bezier
implementation here, it's effectively a freebie to add configurability of the
first and last control points. We do require all control points' x coordinates
to be in ascending order.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
This commit is contained in:
Peter Hutterer
2016-10-24 14:41:51 +10:00
parent f65a5c5022
commit 5d04707381
6 changed files with 229 additions and 3 deletions
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30
man/libinput.man
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@@ -155,6 +155,12 @@ default scroll option for this device is used.
Sets the send events mode to disabled, enabled, or "disable when an external
mouse is connected".
.TP 7
.BI "Option \*qTabletToolPressureCurve\*q \*q" "x0/y0 x1/y1 x2/y2 x3/y3" \*q
Set the pressure curve for a tablet stylus to the bezier formed by the four
points. The respective x/y coordinate must be in the [0.0, 1.0] range. For
more information see section
.B TABLET STYLUS PRESSURE CURVE.
.TP 7
.BI "Option \*qTapping\*q \*q" bool \*q
Enables or disables tap-to-click behavior.
.TP 7
@@ -252,6 +258,11 @@ on this device.
"disabled-on-external-mouse". Indicates which send-event modes is currently
enabled on this device.
.TP 7
.BI "libinput Tablet Tool Pressurecurve"
4 32-bit float values [0.0 to 1.0]. See section
.B TABLET TOOL PRESSURE CURVE
for more information.
.TP 7
.BI "libinput Tapping Enabled"
1 boolean value (8 bit, 0 or 1). 1 enables tapping
.TP 7
@@ -313,6 +324,25 @@ and only the target button events are sent.
.TP
This feature is provided by this driver, not by libinput.
.SH TABLET TOOL PRESSURECURVE
The pressure curve affects how stylus pressure is reported. By default, the
hardware pressure is reported as-is. By setting a pressure curve, the feel
of the stylus can be adjusted to be more like e.g. a pencil or a brush.
.PP
The pressure curve is a cubic Bezier curve, drawn within a normalized range
of 0.0 to 1.0 between the four points provided. This normalized range is
applied to the tablet's pressure input so that the highest pressure maps to
1.0. The points must have increasing x coordinates, if x0 is larger than 0.0
all pressure values lower than x0 are equivalent to y0. If x3 is less than
1.0, all pressure values higher than x3 are equivalent to y3.
The input for a linear curve (default) is "0.0/0.0 0.0/0.0 1.0/1.0 1.0/1.0";
a slightly
depressed curve (firmer) might be "0.0/0.0 0.05/0.0 1.0/0.95 1.0/1.0"; a slightly raised
curve (softer) might be "0.0/0.0 0.0/0.05 0.95/1.0 1.0/1.0".
.TP
This feature is provided by this driver, not by libinput.
.SH AUTHORS
Peter Hutterer
.SH "SEE ALSO"