xf86-input-libinput 0.26.0

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

autogen.sh

@@ -1,14 +1,17 @@
 #! /bin/sh
 
-srcdir=`dirname $0`
+srcdir=`dirname "$0"`
 test -z "$srcdir" && srcdir=.
 
 ORIGDIR=`pwd`
-cd $srcdir
+cd "$srcdir"
 
 autoreconf -v --install || exit 1
-cd $ORIGDIR || exit $?
+cd "$ORIGDIR" || exit $?
+
+git config --local --get format.subjectPrefix >/dev/null 2>&1 ||
+    git config --local format.subjectPrefix "PATCH xf86-input-libinput"
 
 if test -z "$NOCONFIGURE"; then
-    exec $srcdir/configure "$@"
+    exec "$srcdir"/configure "$@"
 fi

conf/40-libinput.conf

@@ -1,4 +1,4 @@
-# Match on all types of devices but tablet devices and joysticks
+# Match on all types of devices but joysticks
 Section "InputClass"
         Identifier "libinput pointer catchall"
         MatchIsPointer "on"
@@ -26,3 +26,10 @@ Section "InputClass"
         MatchDevicePath "/dev/input/event*"
         Driver "libinput"
 EndSection
+
+Section "InputClass"
+        Identifier "libinput tablet catchall"
+        MatchIsTablet "on"
+        MatchDevicePath "/dev/input/event*"
+        Driver "libinput"
+EndSection

configure.ac

@@ -23,7 +23,7 @@
 # Initialize Autoconf
 AC_PREREQ([2.60])
 AC_INIT([xf86-input-libinput],
-        [0.20.0],
+        [0.26.0],
         [https://bugs.freedesktop.org/enter_bug.cgi?product=xorg],
         [xf86-input-libinput])
 AC_CONFIG_SRCDIR([Makefile.am])

include/libinput-properties.h

@@ -183,4 +183,14 @@
 /* Device rotation: FLOAT, 1 value, 32 bit, read-only */
 #define LIBINPUT_PROP_ROTATION_ANGLE_DEFAULT "libinput Rotation Angle Default"
 
+/* Tablet tool pressure curve: float, 8 values, 32 bit
+ * Value range is [0.0, 1.0], the values specify the x/y of the four
+ * control points for a cubic bezier curve.
+ * Default value: 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0
+ */
+#define LIBINPUT_PROP_TABLET_TOOL_PRESSURECURVE "libinput Tablet Tool Pressurecurve"
+
+/* Tablet tool area ratio: CARD32, 2 values, w and h */
+#define LIBINPUT_PROP_TABLET_TOOL_AREA_RATIO "libinput Tablet Tool Area Ratio"
+
 #endif /* _LIBINPUT_PROPERTIES_H_ */

man/libinput.man

@@ -41,15 +41,6 @@ The following driver
 .B Options
 are supported:
 .TP 7
-.BI "Option \*qDevice\*q \*q" string \*q
-Specifies the device through which the device can be accessed.  This will 
-generally be of the form \*q/dev/input/eventX\*q, where X is some integer.
-When using
-.B InputClass
-directives, this option is set by the server.
-The mapping from device node to hardware is system-dependent. Property:
-"Device Node" (read-only).
-.TP 7
 .BI "Option \*qAccelProfile\*q \*q" string \*q
 Sets the pointer acceleration profile to the given profile. Permitted values
 are
@@ -89,72 +80,19 @@ Enables a click method. Permitted values are
 Not all devices support all methods, if an option is unsupported, the
 default click method for this device is used.
 .TP 7
-.BI "Option \*qLeftHanded\*q \*q" bool \*q
-Enables left-handed button orientation, i.e. swapping left and right buttons.
-.TP 7
-.BI "Option \*qMiddleEmulation\*q \*q" bool \*q
-Enables middle button emulation. When enabled, pressing the left and right
-buttons simultaneously produces a middle mouse button click.
-.TP 7
-.BI "Option \*qNaturalScrolling\*q \*q" bool \*q
-Enables or disables natural scrolling behavior.
-.TP 7
-.BI "Option \*qScrollButton\*q \*q" int \*q
-Designates a button as scroll button. If the
-.BI ScrollMethod
-is
-.BI button
-and the button is logically held down, x/y axis movement is converted into
-scroll events.
-.TP 7
-.BI "Option \*qScrollMethod\*q \*q" string \*q
-Enables a scroll method. Permitted values are
-.BI none,
-.BI twofinger,
-.BI edge,
-.BI button.
-Not all devices support all options, if an option is unsupported, the
-default scroll option for this device is used.
-.TP 7
-.BI "Option \*qHorizontalScrolling\*q \*q" bool \*q
-Disables horizontal scrolling. When disabled, this driver will discard any
-horizontal scroll events from libinput. Note that this does not disable
-horizontal scrolling, it merely discards the horizontal axis from any scroll
-events.
-.TP 7
-.BI "Option \*qSendEventsMode\*q \*q" (disabled|enabled|disabled-on-external-mouse) \*q
-Sets the send events mode to disabled, enabled, or "disable when an external
-mouse is connected".
-.TP 7
-.BI "Option \*qRotationAngle\*q \*q" float \*q
-Sets the rotation angle of the device to the given angle, in degrees
-clockwise. The angle must be between 0.0 (inclusive) and 360.0 (exclusive).
-.TP 7
-.BI "Option \*qTapping\*q \*q" bool \*q
-Enables or disables tap-to-click behavior.
-.TP 7
-.BI "Option \*qTappingButtonMap\*q \*q" (lrm|lmr) \*q
-Set the button mapping for 1/2/3-finger taps to left/right/middle or
-left/middle/right, respectively.
-.TP 7
-.BI "Option \*qTappingDrag\*q \*q" bool \*q
-Enables or disables drag during tapping behavior ("tap-and-drag"). When
-enabled, a tap followed by a finger held down causes a single button down
-only, all motions of that finger thus translate into dragging motion.
-Tap-and-drag requires option
-.B Tapping
-to be enabled.
-.TP 7
-.BI "Option \*qTappingDragLock\*q \*q" bool \*q
-Enables or disables drag lock during tapping behavior. When enabled, a
-finger up during tap-and-drag will not immediately release the button. If
-the finger is set down again within the timeout, the dragging process
-continues.
-.TP 7
 .BI "Option \*qDisableWhileTyping\*q \*q" bool \*q
 Indicates if the touchpad should be disabled while typing on the keyboard
 (this does not apply to modifier keys such as Ctrl or Alt).
 .TP 7
+.BI "Option \*qDevice\*q \*q" string \*q
+Specifies the device through which the device can be accessed.  This will
+generally be of the form \*q/dev/input/eventX\*q, where X is some integer.
+When using
+.B InputClass
+directives, this option is set by the server.
+The mapping from device node to hardware is system-dependent. Property:
+"Device Node" (read-only).
+.TP 7
 .BI "Option \*qDragLockButtons\*q \*q" "L1 B1 L2 B2 ..." \*q
 Sets "drag lock buttons" that simulate a button logically down even when it has
 been physically released. To logically release a locked button, a second click
@@ -175,6 +113,82 @@ For both meta and button pair configuration, the button numbers are
 device button numbers, i.e. the
 .B ButtonMapping
 applies after drag lock.
+.TP 7
+.BI "Option \*qHorizontalScrolling\*q \*q" bool \*q
+Disables horizontal scrolling. When disabled, this driver will discard any
+horizontal scroll events from libinput. Note that this does not disable
+horizontal scrolling, it merely discards the horizontal axis from any scroll
+events.
+.TP 7
+.BI "Option \*qLeftHanded\*q \*q" bool \*q
+Enables left-handed button orientation, i.e. swapping left and right buttons.
+.TP 7
+.BI "Option \*qMiddleEmulation\*q \*q" bool \*q
+Enables middle button emulation. When enabled, pressing the left and right
+buttons simultaneously produces a middle mouse button click.
+.TP 7
+.BI "Option \*qNaturalScrolling\*q \*q" bool \*q
+Enables or disables natural scrolling behavior.
+.TP 7
+.BI "Option \*qRotationAngle\*q \*q" float \*q
+Sets the rotation angle of the device to the given angle, in degrees
+clockwise. The angle must be between 0.0 (inclusive) and 360.0 (exclusive).
+.TP 7
+.BI "Option \*qScrollButton\*q \*q" int \*q
+Designates a button as scroll button. If the
+.BI ScrollMethod
+is
+.BI button
+and the button is logically held down, x/y axis movement is converted into
+scroll events.
+.TP 7
+.BI "Option \*qScrollMethod\*q \*q" string \*q
+Enables a scroll method. Permitted values are
+.BI none,
+.BI twofinger,
+.BI edge,
+.BI button.
+Not all devices support all options, if an option is unsupported, the
+default scroll option for this device is used.
+.TP 7
+.BI "Option \*qSendEventsMode\*q \*q" (disabled|enabled|disabled-on-external-mouse) \*q
+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 \*qTabletToolAreaRatio\*q \*q" "w:h" \*q
+Sets the area ratio for a tablet tool. The area always starts at the
+origin (0/0) and expands to the largest available area with the specified
+aspect ratio. Events outside this area are cropped to the area. The special
+value "default" is used for the default mapping (i.e. the device-native
+mapping). For more information see section
+.B TABLET TOOL AREA RATIO.
+.TP 7
+.BI "Option \*qTapping\*q \*q" bool \*q
+Enables or disables tap-to-click behavior.
+.TP 7
+.BI "Option \*qTappingButtonMap\*q \*q" (lrm|lmr) \*q
+Set the button mapping for 1/2/3-finger taps to left/right/middle or
+left/middle/right, respectively.
+.TP 7
+.BI "Option \*qTappingDrag\*q \*q" bool \*q
+Enables or disables drag during tapping behavior ("tap-and-drag"). When
+enabled, a tap followed by a finger held down causes a single button down
+only, all motions of that finger thus translate into dragging motion.
+Tap-and-drag requires option
+.B Tapping
+to be enabled.
+.TP 7
+.BI "Option \*qTappingDragLock\*q \*q" bool \*q
+Enables or disables drag lock during tapping behavior. When enabled, a
+finger up during tap-and-drag will not immediately release the button. If
+the finger is set down again within the timeout, the dragging process
+continues.
 .PP
 For all options, the options are only parsed if the device supports that
 configuration option. For all options, the default value is the one used by
@@ -189,26 +203,67 @@ on the device. The following properties are provided by the
 .B libinput
 driver.
 .TP 7
-.BI "libinput Tapping Enabled"
-1 boolean value (8 bit, 0 or 1). 1 enables tapping
+.BI "libinput Accel Profiles Available"
+2 boolean values (8 bit, 0 or 1), in order "adaptive", "flat".
+Indicates which acceleration profiles are available on this device.
 .TP 7
-.BI "libinput Tapping Button Mapping Enabled"
-2 boolean value (8 bit, 0 or 1), in order "lrm" and "lmr". Indicates which
-button mapping is currently enabled on this device.
+.BI "libinput Accel Profile Enabled"
+2 boolean values (8 bit, 0 or 1), in order "adaptive", "flat".
+Indicates which acceleration profile is currently enabled on this device.
 .TP 7
-.BI "libinput Tapping Drag Lock Enabled"
-1 boolean value (8 bit, 0 or 1). 1 enables drag lock during tapping
+.BI "libinput Accel Speed"
+1 32-bit float value, defines the pointer speed. Value range -1, 1
+.TP 7
+.BI "libinput Button Scrolling Button"
+1 32-bit value. Sets the button number to use for button scrolling. This
+setting is independent of the scroll method, to enable button scrolling the
+method must be set to button-scrolling and a valid button must be set.
 .TP 7
 .BI "libinput Calibration Matrix"
 9 32-bit float values, representing a 3x3 calibration matrix, order is row
 1, row 2, row 3
 .TP 7
-.BI "libinput Accel Speed"
-1 32-bit float value, defines the pointer speed. Value range -1, 1
+.BI "libinput Click Methods Available"
+2 boolean values (8 bit, 0 or 1), in order "buttonareas", "clickfinger".
+Indicates which click methods are available on this device.
+.TP 7
+.BI "libinput Click Methods Enabled"
+2 boolean values (8 bit, 0 or 1), in order "buttonareas", "clickfinger".
+Indicates which click methods are enabled on this device.
+.TP 7
+.BI "libinput Drag Lock Buttons"
+Either one 8-bit value specifying the meta drag lock button, or a list of
+button pairs. See section
+.B BUTTON DRAG LOCK
+for details.
+.TP 7
+.BI "libinput Horizontal Scrolling Enabled"
+1 boolean value (8 bit, 0 or 1). Indicates whether horizontal scrolling
+events are enabled or not.
+.TP 7
+.BI "libinput Left Handed Enabled"
+1 boolean value (8 bit, 0 or 1). Indicates if left-handed mode is enabled or
+disabled.
+.TP 7
+.BI "libinput Middle Emulation Enabled"
+1 boolean value (8 bit, 0 or 1). Indicates if middle emulation is enabled or
+disabled.
 .TP 7
 .BI "libinput Natural Scrolling Enabled"
 1 boolean value (8 bit, 0 or 1). 1 enables natural scrolling
 .TP 7
+.BI "libinput Rotation Angle"
+1 32-bit float value [0.0 to 360.0). Sets the rotation angle of the device,
+clockwise of its natural neutral position.
+.TP 7
+.BI "libinput Scroll Methods Available"
+3 boolean values (8 bit, 0 or 1), in order "two-finger", "edge", "button".
+Indicates which scroll methods are available on this device.
+.TP 7
+.BI "libinput Scroll Method Enabled"
+3 boolean values (8 bit, 0 or 1), in order "two-finger", "edge", "button".
+Indicates which scroll method is currently enabled on this device.
+.TP 7
 .BI "libinput Send Events Modes Available"
 2 boolean values (8 bit, 0 or 1), in order "disabled" and
 "disabled-on-external-mouse". Indicates which send-event modes are available
@@ -219,56 +274,33 @@ on this device.
 "disabled-on-external-mouse". Indicates which send-event modes is currently
 enabled on this device.
 .TP 7
-.BI "libinput Left Handed Enabled"
-1 boolean value (8 bit, 0 or 1). Indicates if left-handed mode is enabled or
-disabled.
+.BI "libinput Tablet Tool Pressurecurve"
+4 32-bit float values [0.0 to 1.0]. See section
+.B TABLET TOOL PRESSURE CURVE
+.TP7
+.BI "libinput Tablet Tool Area Ratio"
+2 32-bit values, corresponding to width and height. Special value 0, 0
+resets to the default ratio. See section
+.B TABLET TOOL AREA RATIO
+for more information.
 .TP 7
-.BI "libinput Scroll Methods Available"
-3 boolean values (8 bit, 0 or 1), in order "two-finger", "edge", "button".
-Indicates which scroll methods are available on this device.
+.BI "libinput Tapping Enabled"
+1 boolean value (8 bit, 0 or 1). 1 enables tapping
 .TP 7
-.BI "libinput Scroll Method Enabled"
-3 boolean values (8 bit, 0 or 1), in order "two-finger", "edge", "button".
-Indicates which scroll method is currently enabled on this device.
+.BI "libinput Tapping Button Mapping Enabled"
+2 boolean value (8 bit, 0 or 1), in order "lrm" and "lmr". Indicates which
+button mapping is currently enabled on this device.
 .TP 7
-.BI "libinput Button Scrolling Button"
-1 32-bit value. Sets the button number to use for button scrolling. This
-setting is independent of the scroll method, to enable button scrolling the
-method must be set to button-scrolling and a valid button must be set.
-.TP 7
-.BI "libinput Click Methods Available"
-2 boolean values (8 bit, 0 or 1), in order "buttonareas", "clickfinger".
-Indicates which click methods are available on this device.
-.TP 7
-.BI "libinput Click Methods Enabled"
-2 boolean values (8 bit, 0 or 1), in order "buttonareas", "clickfinger".
-Indicates which click methods are enabled on this device.
-.TP 7
-.BI "libinput Middle Emulation Enabled"
-1 boolean value (8 bit, 0 or 1). Indicates if middle emulation is enabled or
-disabled.
+.BI "libinput Tapping Drag Lock Enabled"
+1 boolean value (8 bit, 0 or 1). 1 enables drag lock during tapping
 .TP 7
 .BI "libinput Disable While Typing Enabled"
 1 boolean value (8 bit, 0 or 1). Indicates if disable while typing is
 enabled or disabled.
-.TP 7
-.BI "libinput Rotation Angle"
-1 32-bit float value [0.0 to 360.0). Sets the rotation angle of the device,
-clockwise of its natural neutral position.
 .PP
-The above properties have a
+Most properties have a
 .BI "libinput <property name> Default"
 equivalent that indicates the default value for this setting on this device.
-.TP 7
-.BI "libinput Drag Lock Buttons"
-Either one 8-bit value specifying the meta drag lock button, or a list of
-button pairs. See section
-.B BUTTON DRAG LOCK
-for details.
-.TP 7
-.BI "libinput Horizontal Scrolling Enabled"
-1 boolean value (8 bit, 0 or 1). Indicates whether horizontal scrolling
-events are enabled or not.
 
 .SH BUTTON MAPPING
 X clients receive events with logical button numbers, where 1, 2, 3
@@ -313,6 +345,42 @@ 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 TABLET TOOL AREA RATIO
+By default, a tablet tool can access the whole sensor area and the tablet
+area is mapped to the available screen area. For external tablets like
+the Wacom Intuos series, the height:width ratio of the tablet may be
+different to that of the monitor, causing the skew of input data.
+.PP
+To avoid this skew of input data, an area ratio may be set to match the
+ratio of the screen device. For example, a ratio of 4:3 will reduce the
+available area of the tablet to the largest available area with a ratio of
+4:3. Events within this area will scale to the tablet's announced axis
+range, the area ratio is thus transparent to the X server. Any events
+outside this area will send events equal to the maximum value of that axis.
+The area always starts at the device's origin in it's current rotation, i.e.
+it takes left-handed-ness into account.
+.TP
+This feature is provided by this driver, not by libinput.
+
 .SH AUTHORS
 Peter Hutterer
 .SH "SEE ALSO"

src/Makefile.am

@@ -30,10 +30,11 @@ AM_CPPFLAGS =-I$(top_srcdir)/include $(LIBINPUT_CFLAGS)
 
 @DRIVER_NAME@_drv_la_LTLIBRARIES = @DRIVER_NAME@_drv.la
 @DRIVER_NAME@_drv_la_LDFLAGS = -module -avoid-version
-@DRIVER_NAME@_drv_la_LIBADD = $(LIBINPUT_LIBS) libdraglock.la
+@DRIVER_NAME@_drv_la_LIBADD = $(LIBINPUT_LIBS) libdraglock.la libbezier.la -lm
 @DRIVER_NAME@_drv_ladir = @inputdir@
 
 @DRIVER_NAME@_drv_la_SOURCES = xf86libinput.c
 
-noinst_LTLIBRARIES = libdraglock.la
+noinst_LTLIBRARIES = libdraglock.la libbezier.la
 libdraglock_la_SOURCES = draglock.c draglock.h
+libbezier_la_SOURCES = bezier.c bezier.h

src/bezier.c

@@ -0,0 +1,177 @@
+/*
+ * Copyright © 2016 Red Hat, Inc.
+ *
+ * Permission to use, copy, modify, distribute, and sell this software
+ * and its documentation for any purpose is hereby granted without
+ * fee, provided that the above copyright notice appear in all copies
+ * and that both that copyright notice and this permission notice
+ * appear in supporting documentation, and that the name of Red Hat
+ * not be used in advertising or publicity pertaining to distribution
+ * of the software without specific, written prior permission.  Red
+ * Hat makes no representations about the suitability of this software
+ * for any purpose.  It is provided "as is" without express or implied
+ * warranty.
+ *
+ * THE AUTHORS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
+ * NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+ * OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+ * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <assert.h>
+#include <math.h>
+#include <stdio.h>
+
+#include "bezier.h"
+
+const struct bezier_control_point bezier_defaults[4] = {
+	{ 0.0, 0.0 },
+	{ 0.0, 0.0 },
+	{ 1.0, 1.0 },
+	{ 1.0, 1.0 },
+};
+
+struct point {
+	int x, y;
+};
+
+/**
+ * de Casteljau's algorithm. See this page here
+ * https://pomax.github.io/bezierinfo/#extended
+ *
+ * To play with bezier curve shapes, I used
+ * http://cubic-bezier.com/
+ */
+static struct point
+decasteljau(const struct point *controls,
+	    size_t ncontrols,
+	    double t)
+{
+	struct point new_controls[ncontrols];
+
+	if (ncontrols == 1)
+		return controls[0];
+
+	for (int i = 0; i < ncontrols - 1; i++) {
+		new_controls[i].x = (1.0 - t) * controls[i].x + t * controls[i + 1].x;
+		new_controls[i].y = (1.0 - t) * controls[i].y + t * controls[i + 1].y;
+	}
+
+	return decasteljau(new_controls, ncontrols - 1, t);
+}
+
+/**
+ * Given a Bézier curve defined by the control points, reduce the curve to
+ * one with ncurve_points.
+ */
+static void
+flatten_curve(const struct point *controls,
+	      size_t ncontrols,
+	      struct point *curve,
+	      size_t ncurve_points)
+{
+	ncurve_points--; /* make sure we end up with 100/100 as last point */
+
+	for (int i = 0; i <= ncurve_points; i++) {
+		double t = 1.0 * i/ncurve_points;
+		struct point p;
+
+		p = decasteljau(controls, ncontrols, t);
+		curve[i] = p;
+	}
+}
+
+/**
+ * Calculate line through a and b, set curve[x] for each x between
+ * [a.x,  b.x].
+ *
+ * Note: pcurve must be at least b.x size.
+ */
+static void
+line_between(struct point a, struct point b,
+	     struct point *curve, size_t curve_sz)
+{
+	double slope;
+	double offset;
+
+	assert(b.x < curve_sz);
+
+	if (a.x == b.x) {
+		curve[a.x].x = a.x;
+		curve[a.x].y = a.y;
+		return;
+	}
+
+	slope = (double)(b.y - a.y)/(b.x - a.x);
+	offset = a.y - slope * a.x;
+
+	for (int x = a.x; x <= b.x; x++) {
+		struct point p;
+		p.x = x;
+		p.y = slope * x + offset;
+		curve[x] = p;
+	}
+}
+
+bool
+cubic_bezier(const struct bezier_control_point controls[4],
+	     int *bezier_out,
+	     size_t bezier_sz)
+{
+	const int nsegments = 50;
+	const int range = bezier_sz - 1;
+	struct point curve[nsegments];
+	struct point bezier[bezier_sz];
+	struct point zero = { 0, 0 },
+		     max = { range, range};
+
+	/* Scale control points into the [0, bezier_sz) range */
+	struct point ctrls[4];
+
+	for (int i = 0; i < 4; i++) {
+		if (controls[i].x < 0.0 || controls[i].x > 1.0 ||
+		    controls[i].y < 0.0 || controls[i].y > 1.0)
+			return false;
+
+		ctrls[i].x = controls[i].x * range;
+		ctrls[i].y = controls[i].y * range;
+	}
+
+	for (int i = 0; i < 3; i++) {
+		if (ctrls[i].x > ctrls[i+1].x)
+			return false;
+	}
+
+	/* Reduce curve to nsegments, because this isn't a drawing program */
+	flatten_curve(ctrls, 4, curve, nsegments);
+
+	/* we now have nsegments points in curve that represent the bezier
+	   curve (already in the [0, bezier_sz) range). Run through the
+	   points and draw a straight line between each point and voila, we
+	   have our curve.
+
+	   If the first control points (x0/y0) is not at x == 0 or the last
+	   control point (x3/y3) is not at the max value, draw a line
+	   between from 0/0 to x0/y0 and from x3/y3 to xmax/y3.
+	 */
+
+	line_between(zero, curve[0], bezier, bezier_sz);
+
+	for (int i = 0; i < nsegments - 1; i++)
+		line_between(curve[i], curve[i+1], bezier, bezier_sz);
+
+	if (curve[nsegments - 1].x < max.x)
+		line_between(curve[nsegments - 1], max, bezier, bezier_sz);
+
+	for (int i = 0; i < bezier_sz; i++)
+		bezier_out[i] = bezier[i].y;
+
+	return true;
+}

src/bezier.h

@@ -0,0 +1,69 @@
+/*
+ * Copyright © 2016 Red Hat, Inc.
+ *
+ * Permission to use, copy, modify, distribute, and sell this software
+ * and its documentation for any purpose is hereby granted without
+ * fee, provided that the above copyright notice appear in all copies
+ * and that both that copyright notice and this permission notice
+ * appear in supporting documentation, and that the name of Red Hat
+ * not be used in advertising or publicity pertaining to distribution
+ * of the software without specific, written prior permission.  Red
+ * Hat makes no representations about the suitability of this software
+ * for any purpose.  It is provided "as is" without express or implied
+ * warranty.
+ *
+ * THE AUTHORS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
+ * NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+ * OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+ * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#ifndef BEZIER_H
+#define BEZIER_H
+
+#include <stdlib.h>
+#include <stdbool.h>
+
+struct bezier_control_point {
+	double x, y;
+};
+
+extern const struct bezier_control_point bezier_defaults[4];
+
+/**
+ * Given four control points in the range [(0.0/0.0), (1.0/1.0)]
+ * construct a Bézier curve.
+ *
+ *    ^
+ *1.0 |    c2 ______ c3
+ *    |     _/
+ *    |    /
+ *    |c1 /
+ *    |  /
+ *    | /
+ *    |/_________________>
+ *    c0           1.0
+ *
+ * This function requires that c[i].x <= c[i+1].x
+ *
+ * The curve is mapped into a canvas size [0, bezier_sz)². For each x
+ * coordiante in [0, bezier_sz), the matching y coordinate is thus
+ * bezier[x].
+ *
+ * In other words, if you have a range [0,2048) input possible values,
+ * the output is a list of 2048 points in a [0, 2048) range.
+ *
+ * @return true on success, false otherwise
+ */
+bool
+cubic_bezier(const struct bezier_control_point controls[4],
+	     int *bezier,
+	     size_t bezier_sz);
+#endif

test/Makefile.am

@@ -3,11 +3,14 @@ AM_CPPFLAGS = $(XORG_CFLAGS) \
 	      -I$(top_srcdir)/include \
 	      -I$(top_srcdir)/src
 
-tests = test-draglock
+tests = test-draglock test-bezier
 
 noinst_PROGRAMS = $(tests)
 
 test_draglock_SOURCES = test-draglock.c
 test_draglock_LDADD = ../src/libdraglock.la
 
+test_bezier_SOURCES = test-bezier.c
+test_bezier_LDADD = ../src/libbezier.la -lm
+
 TESTS = $(tests)

test/test-bezier.c

@@ -0,0 +1,206 @@
+/*
+ * Copyright © 2016 Red Hat, Inc.
+ *
+ * Permission to use, copy, modify, distribute, and sell this software
+ * and its documentation for any purpose is hereby granted without
+ * fee, provided that the above copyright notice appear in all copies
+ * and that both that copyright notice and this permission notice
+ * appear in supporting documentation, and that the name of Red Hat
+ * not be used in advertising or publicity pertaining to distribution
+ * of the software without specific, written prior permission.  Red
+ * Hat makes no representations about the suitability of this software
+ * for any purpose.  It is provided "as is" without express or implied
+ * warranty.
+ *
+ * THE AUTHORS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
+ * NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+ * OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+ * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "bezier.h"
+
+#include <assert.h>
+#include <string.h>
+#include <stdio.h>
+
+static inline void
+print_curve(int *bezier, size_t size)
+{
+	/* look at it with gnuplot, "plot 'output-file.txt'" */
+	for (int i = 0; i < size; i++)
+		printf("%d %d\n", i, bezier[i]);
+}
+
+static void
+test_linear(void)
+{
+	const int size = 2048;
+	int bezier[size];
+
+	struct bezier_control_point controls[] = {
+		{ 0.0, 0.0 },
+		{ 0.0, 0.0 },
+		{ 1.0, 1.0 },
+		{ 1.0, 1.0 }
+	};
+
+	cubic_bezier(controls, bezier, size);
+
+	assert(bezier[0] == 0);
+	assert(bezier[size - 1] == size - 1);
+
+	for (int x = 1; x < size; x++)
+		assert(bezier[x] == x);
+}
+
+/* Center point pulled down towards X axis */
+static void
+test_flattened(void)
+{
+	const int size = 2048;
+	int bezier[size];
+
+	struct bezier_control_point controls[] = {
+		{ 0.0, 0.0 },
+		{ 0.1, 0.0 },
+		{ 1.0, 0.9 },
+		{ 1.0, 1.0 }
+	};
+
+	cubic_bezier(controls, bezier, size);
+
+	assert(bezier[0] == 0);
+	assert(bezier[size - 1] == size - 1);
+
+	for (int x = 1; x < size - 1; x++) {
+		assert(bezier[x] < x);
+	}
+}
+
+/* Center point pulled up from X axis */
+static void
+test_raised(void)
+{
+	const int size = 2048;
+	int bezier[size];
+
+	struct bezier_control_point controls[] = {
+		{ 0.0, 0.0 },
+		{ 0.1, 0.4 },
+		{ 0.4, 1.0 },
+		{ 1.0, 1.0 }
+	};
+
+	cubic_bezier(controls, bezier, size);
+
+	assert(bezier[0] == 0);
+	assert(bezier[size - 1] == size - 1);
+
+	for (int x = 1; x < size; x++)
+		assert(bezier[x] >= x);
+
+	for (int x = 10; x < size - 10; x++)
+		assert(bezier[x] > x);
+}
+
+static void
+test_windy(void)
+{
+	const int size = 2048;
+	int bezier[size];
+
+	struct bezier_control_point controls[] = {
+		{ 0.0, 0.0 },
+		{ 0.0, 0.3 },
+		{ 1.0, 0.7 },
+		{ 1.0, 1.0 }
+	};
+
+	cubic_bezier(controls, bezier, size);
+
+	assert(bezier[0] == 0);
+	assert(bezier[size - 1] == size - 1);
+
+	for (int x = 1; x < size/2 - 20; x++)
+		assert(bezier[x] > x);
+
+	for (int x = size/2 + 20; x < size - 1; x++)
+		assert(bezier[x] < x);
+}
+
+static void
+test_nonzero_x_linear(void)
+{
+	const int size = 2048;
+	int bezier[size];
+	int x;
+
+	struct bezier_control_point controls[] = {
+		{ 0.2, 0.0 },
+		{ 0.2, 0.0 },
+		{ 0.8, 1.0 },
+		{ 0.8, 1.0 }
+	};
+
+	cubic_bezier(controls, bezier, size);
+
+	x = 0;
+	do {
+		assert(bezier[x] == 0);
+	} while (++x < size * 0.2 - 1);
+
+	/* ppc64le, ppc64, aarch64 have different math results at -O2,
+	   resulting in one extra zero at the beginning of the array.
+	   some other numbers are different too but within the error
+	   margin (#99992) */
+	if (bezier[x] == 0)
+		x++;
+
+	do {
+		assert(bezier[x] > bezier[x-1]);
+	} while (++x < size * 0.8 - 1);
+
+	do {
+		assert(bezier[x] == size - 1);
+	} while (++x < size);
+}
+
+static void
+test_nonzero_y_linear(void)
+{
+	const int size = 2048;
+	int bezier[size];
+
+	struct bezier_control_point controls[] = {
+		{ 0.0, 0.2 },
+		{ 0.0, 0.2 },
+		{ 1.0, 0.8 },
+		{ 1.0, 0.8 }
+	};
+
+	cubic_bezier(controls, bezier, size);
+
+	assert(bezier[0] == (int)(size * 0.2));
+
+	for (int x = 1; x < size; x++) {
+		assert(bezier[x - 1] <= bezier[x]);
+		assert(bezier[x] >= (int)(size * 0.2));
+	}
+}
+
+int
+main(int argc, char **argv)
+{
+	test_linear();
+	test_flattened();
+	test_raised();
+	test_windy();
+	test_nonzero_x_linear();
+	test_nonzero_y_linear();
+
+	return 0;
+}