add scroll button option

This commit introduces a scroll_button option, which is intended to be
used with scroll_method. Now user can edit his sway config and add an
scroll_button option to device section.

include/sway/commands.h

@@ -207,6 +207,7 @@ sway_cmd input_cmd_natural_scroll;
 sway_cmd input_cmd_pointer_accel;
 sway_cmd input_cmd_repeat_delay;
 sway_cmd input_cmd_repeat_rate;
+sway_cmd input_cmd_scroll_button;
 sway_cmd input_cmd_scroll_method;
 sway_cmd input_cmd_tap;
 sway_cmd input_cmd_xkb_layout;

include/sway/config.h

@@ -75,6 +75,7 @@ struct input_config {
 	float pointer_accel;
 	int repeat_delay;
 	int repeat_rate;
+	int scroll_button;
 	int scroll_method;
 	int send_events;
 	int tap;

sway/commands/input.c

@@ -20,6 +20,7 @@ static struct cmd_handler input_handlers[] = {
 	{ "pointer_accel", input_cmd_pointer_accel },
 	{ "repeat_delay", input_cmd_repeat_delay },
 	{ "repeat_rate", input_cmd_repeat_rate },
+	{ "scroll_button", input_cmd_scroll_button },
 	{ "scroll_method", input_cmd_scroll_method },
 	{ "tap", input_cmd_tap },
 	{ "xkb_layout", input_cmd_xkb_layout },

sway/commands/input/scroll_button.c

@@ -0,0 +1,31 @@
+#include <string.h>
+#include <strings.h>
+#include "sway/config.h"
+#include "sway/commands.h"
+#include "sway/input/input-manager.h"
+
+struct cmd_results *input_cmd_scroll_button(int argc, char **argv) {
+	struct cmd_results *error = NULL;
+	if ((error = checkarg(argc, "scroll_button", EXPECTED_AT_LEAST, 1))) {
+		return error;
+	}
+	struct input_config *current_input_config =
+		config->handler_context.input_config;
+	if (!current_input_config) {
+		return cmd_results_new(CMD_FAILURE, "scroll_button",
+			"No input device defined.");
+	}
+	struct input_config *new_config =
+		new_input_config(current_input_config->identifier);
+
+	int scroll_button = atoi(argv[0]);
+	if (scroll_button < 1 || scroll_button > 10) {
+		free_input_config(new_config);
+		return cmd_results_new(CMD_INVALID, "scroll_button",
+				"Input out of range [1, 10]");
+	}
+	new_config->scroll_button = scroll_button;
+
+	apply_input_config(new_config);
+	return cmd_results_new(CMD_SUCCESS, NULL, NULL);
+}

sway/config/input.c

@@ -28,6 +28,7 @@ struct input_config *new_input_config(const char* identifier) {
 	input->accel_profile = INT_MIN;
 	input->pointer_accel = FLT_MIN;
 	input->scroll_method = INT_MIN;
+	input->scroll_button = INT_MIN;
 	input->left_handed = INT_MIN;
 	input->repeat_delay = INT_MIN;
 	input->repeat_rate = INT_MIN;
@@ -70,6 +71,9 @@ void merge_input_config(struct input_config *dst, struct input_config *src) {
 	if (src->scroll_method != INT_MIN) {
 		dst->scroll_method = src->scroll_method;
 	}
+	if (src->scroll_button != INT_MIN) {
+		dst->scroll_button= src->scroll_button;
+	}
 	if (src->send_events != INT_MIN) {
 		dst->send_events = src->send_events;
 	}

sway/input/input-manager.c

@@ -158,6 +158,12 @@ static void input_manager_libinput_config_pointer(
 		libinput_device_config_accel_set_speed(libinput_device,
 			ic->pointer_accel);
 	}
+	if (ic->scroll_button != INT_MIN) {
+		wlr_log(WLR_DEBUG, "libinput_config_pointer(%s) scroll_set_button(%d)",
+			ic->identifier, ic->scroll_button);
+		libinput_device_config_scroll_set_button(libinput_device,
+			ic->scroll_button);
+	}
 	if (ic->scroll_method != INT_MIN) {
 		wlr_log(WLR_DEBUG, "libinput_config_pointer(%s) scroll_set_method(%d)",
 			ic->identifier, ic->scroll_method);

sway/meson.build

@@ -118,6 +118,7 @@ sway_sources = files(
 	'commands/input/pointer_accel.c',
 	'commands/input/repeat_delay.c',
 	'commands/input/repeat_rate.c',
+	'commands/input/scroll_button.c',
 	'commands/input/scroll_method.c',
 	'commands/input/tap.c',
 	'commands/input/xkb_layout.c',