Add a pressurecurve debugging tool

This tool takes (one or multiple) sets of 4 coordinate that represent
the second and third point for our pressure curve (first and fourth
points are hardcoded to 0/0 and 1/1 like the driver does)

It spits out gnuplot-compatible lines that can be printed for visual
debugging. Usage to print the GNOME default curves:

./build/pressurecurve \
    0 .75 .25 1 \
    0 .5 .5 1  \
    0 .25 .75 1 \
    0 0 1 1 \
    .25 0 1 .75 \
    .5 0 1 .5 \
    .75 0 1 .25 > gnuplot.data

And that gnuplot data can then be printed with:

 #!/usr/bin/gnuplot
 set terminal qt persist
 set style data lines
 set xrange [0:1]
 set yrange [0:1]
 plot \
  "gnuplot.data" using 1:2 title "  0, .75, .25, 1", \
  "gnuplot.data" using 1:3 title "  0, .50, .50, 1", \
  "gnuplot.data" using 1:4 title "  0, .25, .75, 1", \
  "gnuplot.data" using 1:5 title "  0,   0,   1, 1", \
  "gnuplot.data" using 1:6 title ".25, 0,   1, .75", \
  "gnuplot.data" using 1:7 title ".50, 0,   1, .50", \
  "gnuplot.data" using 1:8 title ".75, 0,   1, .25"

meson.build

@@ -295,6 +295,13 @@ executable(
 	install: true,
 )
 
+executable(
+	'pressurecurve',
+	['tools/pressurecurve.c',
+	 'src/wcmPressureCurve.c'],
+	include_directories: [dir_src],
+	install: false)
+
 # Man pages
 config_man = configuration_data()
 config_man.set('VERSION', '@0@ @1@'.format(meson.project_name(), meson.project_version()))

tools/Makefile.am

@@ -46,4 +46,4 @@ xsetwacom_test_LDADD = $(X11_LIBS)
 TESTS=$(check_PROGRAMS)
 endif
 
-EXTRA_DIST = wacom-record.c
+EXTRA_DIST = wacom-record.c pressurecurve.c

tools/pressurecurve.c

@@ -0,0 +1,114 @@
+/*
+ * Copyright 2023 Red Hat, Inc
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+#include <config.h>
+
+#include <assert.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "wcmPressureCurve.h"
+
+static void
+usage(void) {
+	printf("Usage: pressurecurve [OPTIONS] x1 y1 x2 y2 ...\n");
+	printf("\n");
+	printf("This tool takes four coordinates in the range [0.0, 1.0] representing \n"
+	       "the driver's pressure curve configuration.\n"
+	       "The output contains one line with input pressure and output pressure for\n"
+	       "each normalized [0.0, 1.0] input pressure value\n"
+	       "\n"
+	       "Multiple sets of 4 coordinates may be given \n");
+}
+
+int main(int argc, char **argv)
+{
+	/* The driver pre-calculates the pressurecurve for each possible
+	 * pressure value. Typically this is 2k or 8k for newer pens, here
+	 * we use 1000 points to get smooth gnuplot output.
+	 *
+	 * The value in filterCurveToLine() is normalized into this range so
+	 * the curve will have values in the range [0, 1000].
+	 */
+	const size_t npoints = 1000;
+
+	/* These two are hardcoded by the driver */
+	const double x0 = 0.0, y0 = 0.0;
+	const double x3 = 1.0, y3 = 1.0;
+
+	enum {
+		OPT_HELP,
+	};
+
+	static struct option long_options[] = {
+		{"help", no_argument, 0, OPT_HELP},
+		{0, 0, 0, 0},
+	};
+
+	int c;
+	while (1)
+	{
+		int option_index = 0;
+
+		c = getopt_long(argc, argv, "", long_options, &option_index);
+		if (c == -1)
+			break;
+		switch (c) {
+		case OPT_HELP:
+			usage();
+			return 0;
+		default:
+			break;
+		}
+	}
+
+	if (optind + 4 > argc || (argc - optind) % 4 != 0) {
+		usage();
+		return 1;
+
+	}
+
+	size_t ncurves = (argc - optind) / 4;
+	int curve[ncurves][npoints];
+	int idx = 0;
+
+	printf("# column 0: input pressure value [0,1]\n");
+	while (optind < argc)
+	{
+		double x1 = atof(argv[optind++]);
+		double y1 = atof(argv[optind++]);
+		double x2 = atof(argv[optind++]);
+		double y2 = atof(argv[optind++]);
+
+		filterCurveToLine(curve[idx], npoints, x0, y0, x1, y1, x2, y2, x3, y3);
+
+		printf("# column %d: %f/%f %f/%f %f/%f %f/%f\n", idx, x0, y0, x1, y1, x2, y2, x3, y3);
+		idx++;
+	}
+
+	for (size_t i = 0; i < npoints; i++)
+	{
+		printf("%f", i/(double)npoints);
+		for (size_t j = 0; j < ncurves; j++)
+			printf(" %f", curve[j][i]/(double)npoints);
+		printf("\n");
+	}
+
+	return 0;
+}