backend/libinput: Manage tablet tool livetimes

This adds the management code to manage tablet tools lifetimes from
libinput.
It follows the suggestion made in the tablet-unstable-v2.xml to destroy
tablet_tools once all tablets that it got into contact with were removed
from the system. This is implemented via a refcount.

If a tool is *not* unique, it will be destroyed on proximity out. This
is libinput specific and mentioned in libinput docs that tools will not
be found again, so we shouldn't keep a reference to them.
Also they can't be on other tablets as well, because they cannot be
tracked.

The naming in this commit is a bit off (to not break things).
The wlr names stay the same, tablet_tool is the libinput_device with
capaiblity LIBINPUT_DEVICE_CAP_TABLET_TOOL which is more akin to
"tablet" in the tablet-unstable-v2 protocol.
The struct that corresponds to the tablet_tool in tablet-unstable-v2 is
called tablet_tool_tool, a rename should be done at some point in the
future.

backend/libinput/events.c

@@ -186,6 +186,9 @@ static void handle_device_removed(struct wlr_libinput_backend *backend,
 	}
 	struct wlr_input_device *dev, *tmp_dev;
 	wl_list_for_each_safe(dev, tmp_dev, wlr_devices, link) {
+		if (dev->type == WLR_INPUT_DEVICE_TABLET_TOOL) {
+			wlr_libinput_tablet_tool_destroy(dev);
+		}
 		wlr_input_device_destroy(dev);
 	}
 	for (size_t i = 0; i < backend->wlr_device_lists.length; i++) {

backend/libinput/tablet_tool.c

@@ -1,6 +1,7 @@
 #include <assert.h>
 #include <libinput.h>
 #include <stdlib.h>
+#include <wayland-util.h>
 #include <wlr/backend/session.h>
 #include <wlr/interfaces/wlr_tablet_tool.h>
 #include <wlr/types/wlr_input_device.h>
@@ -8,7 +9,57 @@
 #include "backend/libinput.h"
 #include "util/signal.h"
 
-struct wlr_tablet_tool *create_libinput_tablet_tool(
+struct wlr_libinput_tablet_tool {
+	struct wlr_tablet_tool_tool wlr_tool;
+
+	struct libinput_tablet_tool *libinput_tool;
+
+	bool unique;
+	// Refcount for destroy + release
+	size_t pad_refs;
+};
+
+// TODO: Maybe this should be a wlr_list? Do we keep it, or want to get rid of
+// it?
+struct tablet_tool_list_elem {
+	struct wl_list link;
+
+	struct wlr_libinput_tablet_tool *tool;
+};
+
+struct wlr_libinput_tablet {
+	struct wlr_tablet_tool wlr_tool;
+
+	struct wl_list tools; // tablet_tool_list_elem::link
+};
+
+static void destroy_tool_tool(struct wlr_libinput_tablet_tool *tool) {
+	wlr_signal_emit_safe(&tool->wlr_tool.events.destroy, &tool->wlr_tool);
+	libinput_tablet_tool_ref(tool->libinput_tool);
+	libinput_tablet_tool_set_user_data(tool->libinput_tool, NULL);
+	free(tool);
+}
+
+
+void wlr_libinput_tablet_tool_destroy(struct wlr_input_device *wlr_dev) {
+	struct wlr_libinput_tablet *tablet =
+		wl_container_of(wlr_dev->tablet_tool, tablet, wlr_tool);
+
+	struct tablet_tool_list_elem *pos;
+	struct tablet_tool_list_elem *tmp;
+	wl_list_for_each_safe(pos, tmp, &tablet->tools, link) {
+		wl_list_remove(&pos->link);
+		struct wlr_libinput_tablet_tool *tool = pos->tool;
+
+		if (--tool->pad_refs == 0) {
+			destroy_tool_tool(tool);
+		}
+
+		free(pos);
+	}
+}
+
+struct wlr_tablet_tool *wlr_libinput_tablet_tool_create(
 		struct libinput_device *libinput_dev) {
 	assert(libinput_dev);
 	struct wlr_tablet_tool *wlr_tablet_tool = calloc(1, sizeof(struct wlr_tablet_tool));
@@ -20,6 +71,91 @@ struct wlr_tablet_tool *create_libinput_tablet_tool(
 	return wlr_tablet_tool;
 }
 
+static enum wlr_tablet_tool_type wlr_type_from_libinput_type(
+		enum libinput_tablet_tool_type value) {
+	switch (value) {
+	case LIBINPUT_TABLET_TOOL_TYPE_PEN:
+		return WLR_TABLET_TOOL_TYPE_PEN;
+	case LIBINPUT_TABLET_TOOL_TYPE_ERASER:
+		return WLR_TABLET_TOOL_TYPE_ERASER;
+	case LIBINPUT_TABLET_TOOL_TYPE_BRUSH:
+		return WLR_TABLET_TOOL_TYPE_BRUSH;
+	case LIBINPUT_TABLET_TOOL_TYPE_PENCIL:
+		return WLR_TABLET_TOOL_TYPE_PENCIL;
+	case LIBINPUT_TABLET_TOOL_TYPE_AIRBRUSH:
+		return WLR_TABLET_TOOL_TYPE_AIRBRUSH;
+	case LIBINPUT_TABLET_TOOL_TYPE_MOUSE:
+		return WLR_TABLET_TOOL_TYPE_MOUSE;
+	case LIBINPUT_TABLET_TOOL_TYPE_LENS:
+		return WLR_TABLET_TOOL_TYPE_LENS;
+	}
+
+	assert(false && "UNREACHABLE");
+}
+
+static struct wlr_libinput_tablet_tool *get_wlr_tablet_tool(
+		struct libinput_tablet_tool *tool) {
+	struct wlr_libinput_tablet_tool *ret =
+		libinput_tablet_tool_get_user_data(tool);
+
+	if (ret) {
+		return ret;
+	}
+
+	ret = calloc(1, sizeof(struct wlr_libinput_tablet_tool));
+	if (!ret) {
+		return NULL;
+	}
+
+	ret->libinput_tool = libinput_tablet_tool_ref(tool);
+	ret->wlr_tool.pressure = libinput_tablet_tool_has_pressure(tool);
+	ret->wlr_tool.distance = libinput_tablet_tool_has_distance(tool);
+	ret->wlr_tool.tilt = libinput_tablet_tool_has_tilt(tool);
+	ret->wlr_tool.rotation = libinput_tablet_tool_has_rotation(tool);
+	ret->wlr_tool.slider = libinput_tablet_tool_has_slider(tool);
+	ret->wlr_tool.wheel = libinput_tablet_tool_has_wheel(tool);
+
+	ret->wlr_tool.hardware_serial = libinput_tablet_tool_get_serial(tool);
+	ret->wlr_tool.hardware_wacom = libinput_tablet_tool_get_tool_id(tool);
+	ret->wlr_tool.type = wlr_type_from_libinput_type(
+		libinput_tablet_tool_get_type(tool));
+
+	ret->unique = libinput_tablet_tool_is_unique(tool);
+
+	wl_signal_init(&ret->wlr_tool.events.destroy);
+
+	libinput_tablet_tool_set_user_data(tool, ret);
+	return ret;
+}
+
+static void ensure_tool_reference(struct wlr_libinput_tablet_tool *tool,
+		struct wlr_tablet_tool *wlr_dev) {
+	struct tablet_tool_list_elem *pos;
+	struct wlr_libinput_tablet *tablet = wl_container_of(wlr_dev, tablet, wlr_tool);
+
+	wl_list_for_each(pos, &tablet->tools, link) {
+		if (pos->tool == tool) { // We already have a ref
+			// XXX: We *could* optimize the tool to the front of
+			// the list here, since we will probably get the next
+			// couple of events from the same tool.
+			// BUT the list should always be rather short (probably
+			// single digit amount of tools) so it might be more
+			// work than it saves
+			return;
+		}
+	}
+
+	struct tablet_tool_list_elem *new =
+		calloc(1, sizeof(struct tablet_tool_list_elem));
+	if (!new) {// TODO: Should we at least log?
+		return;
+	}
+
+	new->tool = tool;
+	wl_list_insert(&tablet->tools, &new->link);
+	++tool->pad_refs;
+}
+
 void handle_tablet_tool_axis(struct libinput_event *event,
 		struct libinput_device *libinput_dev) {
 	struct wlr_input_device *wlr_dev =
@@ -31,7 +167,12 @@ void handle_tablet_tool_axis(struct libinput_event *event,
 	struct libinput_event_tablet_tool *tevent =
 		libinput_event_get_tablet_tool_event(event);
 	struct wlr_event_tablet_tool_axis wlr_event = { 0 };
+	struct wlr_libinput_tablet_tool *tool = get_wlr_tablet_tool(
+		libinput_event_tablet_tool_get_tool(tevent));
+	ensure_tool_reference(tool, wlr_dev->tablet_tool);
+
 	wlr_event.device = wlr_dev;
+	wlr_event.tool = &tool->wlr_tool;
 	wlr_event.time_msec =
 		usec_to_msec(libinput_event_tablet_tool_get_time_usec(tevent));
 	if (libinput_event_tablet_tool_x_has_changed(tevent)) {
@@ -84,6 +225,11 @@ void handle_tablet_tool_proximity(struct libinput_event *event,
 	struct libinput_event_tablet_tool *tevent =
 		libinput_event_get_tablet_tool_event(event);
 	struct wlr_event_tablet_tool_proximity wlr_event = { 0 };
+	struct wlr_libinput_tablet_tool *tool = get_wlr_tablet_tool(
+		libinput_event_tablet_tool_get_tool(tevent));
+	ensure_tool_reference(tool, wlr_dev->tablet_tool);
+
+	wlr_event.tool = &tool->wlr_tool;
 	wlr_event.device = wlr_dev;
 	wlr_event.time_msec =
 		usec_to_msec(libinput_event_tablet_tool_get_time_usec(tevent));
@@ -97,6 +243,27 @@ void handle_tablet_tool_proximity(struct libinput_event *event,
 		break;
 	}
 	wlr_signal_emit_safe(&wlr_dev->tablet_tool->events.proximity, &wlr_event);
+
+	// If the tool is not unique, libinput will not find it again after the
+	// proximity out, so we should destroy it
+	if (!tool->unique) {
+		// The tool isn't unique, it can't be on multiple tablets
+		assert(tool->pad_refs == 1);
+		struct wlr_libinput_tablet *tablet =
+			wl_container_of(wlr_dev->tablet_tool, tablet, wlr_tool);
+		struct tablet_tool_list_elem *pos;
+		struct tablet_tool_list_elem *tmp;
+
+		wl_list_for_each_safe(pos, tmp, &tablet->tools, link) {
+			if (pos->tool == tool) {
+				wl_list_remove(&pos->link);
+				free(pos);
+				break;
+			}
+		}
+
+		destroy_tool_tool(tool);
+	}
 }
 
 void handle_tablet_tool_tip(struct libinput_event *event,
@@ -111,7 +278,12 @@ void handle_tablet_tool_tip(struct libinput_event *event,
 	struct libinput_event_tablet_tool *tevent =
 		libinput_event_get_tablet_tool_event(event);
 	struct wlr_event_tablet_tool_tip wlr_event = { 0 };
+	struct wlr_libinput_tablet_tool *tool = get_wlr_tablet_tool(
+		libinput_event_tablet_tool_get_tool(tevent));
+	ensure_tool_reference(tool, wlr_dev->tablet_tool);
+
 	wlr_event.device = wlr_dev;
+	wlr_event.tool = &tool->wlr_tool;
 	wlr_event.time_msec =
 		usec_to_msec(libinput_event_tablet_tool_get_time_usec(tevent));
 	switch (libinput_event_tablet_tool_get_tip_state(tevent)) {
@@ -137,7 +309,12 @@ void handle_tablet_tool_button(struct libinput_event *event,
 	struct libinput_event_tablet_tool *tevent =
 		libinput_event_get_tablet_tool_event(event);
 	struct wlr_event_tablet_tool_button wlr_event = { 0 };
+	struct wlr_libinput_tablet_tool *tool = get_wlr_tablet_tool(
+		libinput_event_tablet_tool_get_tool(tevent));
+	ensure_tool_reference(tool, wlr_dev->tablet_tool);
+
 	wlr_event.device = wlr_dev;
+	wlr_event.tool = &tool->wlr_tool;
 	wlr_event.time_msec =
 		usec_to_msec(libinput_event_tablet_tool_get_time_usec(tevent));
 	wlr_event.button = libinput_event_tablet_tool_get_button(tevent);

include/backend/libinput.h

@@ -67,6 +67,7 @@ void handle_touch_cancel(struct libinput_event *event,
 
 struct wlr_tablet_tool *create_libinput_tablet_tool(
 		struct libinput_device *device);
+void wlr_libinput_tablet_tool_destroy(struct wlr_input_device *device);
 void handle_tablet_tool_axis(struct libinput_event *event,
 		struct libinput_device *device);
 void handle_tablet_tool_proximity(struct libinput_event *event,

include/wlr/types/wlr_tablet_tool.h

@@ -5,6 +5,41 @@
 #include <wayland-server.h>
 #include <wlr/types/wlr_input_device.h>
 
+/*
+ * Copy+Paste from libinput, but this should neither use libinput, nor
+ * tablet-unstable-v2 headers, so we can't include them
+ */
+enum wlr_tablet_tool_type {
+	WLR_TABLET_TOOL_TYPE_PEN = 1,	/**< A generic pen */
+	WLR_TABLET_TOOL_TYPE_ERASER,	/**< Eraser */
+	WLR_TABLET_TOOL_TYPE_BRUSH,	/**< A paintbrush-like tool */
+	WLR_TABLET_TOOL_TYPE_PENCIL,	/**< Physical drawing tool, e.g.
+				             Wacom Inking Pen */
+	WLR_TABLET_TOOL_TYPE_AIRBRUSH,	/**< An airbrush-like tool */
+	WLR_TABLET_TOOL_TYPE_MOUSE,	/**< A mouse bound to the tablet */
+	WLR_TABLET_TOOL_TYPE_LENS,		/**< A mouse tool with a lens */
+};
+
+struct wlr_tablet_tool_tool {
+	enum wlr_tablet_tool_type type;
+	uint64_t hardware_serial;
+	uint64_t hardware_wacom;
+
+	// Capabilities
+	bool tilt;
+	bool pressure;
+	bool distance;
+	bool rotation;
+	bool slider;
+	bool wheel;
+
+	struct {
+		struct wl_signal destroy;
+	} events;
+	
+	void *data;
+};
+
 struct wlr_tablet_tool_impl;
 
 struct wlr_tablet_tool {
@@ -34,6 +69,8 @@ enum wlr_tablet_tool_axes {
 
 struct wlr_event_tablet_tool_axis {
 	struct wlr_input_device *device;
+	struct wlr_tablet_tool_tool *tool;
+
 	uint32_t time_msec;
 	uint32_t updated_axes;
 	// From 0..1
@@ -53,6 +90,7 @@ enum wlr_tablet_tool_proximity_state {
 
 struct wlr_event_tablet_tool_proximity {
 	struct wlr_input_device *device;
+	struct wlr_tablet_tool_tool *tool;
 	uint32_t time_msec;
 	// From 0..1
 	double x, y;
@@ -66,6 +104,7 @@ enum wlr_tablet_tool_tip_state {
 
 struct wlr_event_tablet_tool_tip {
 	struct wlr_input_device *device;
+	struct wlr_tablet_tool_tool *tool;
 	uint32_t time_msec;
 	// From 0..1
 	double x, y;
@@ -74,6 +113,7 @@ struct wlr_event_tablet_tool_tip {
 
 struct wlr_event_tablet_tool_button {
 	struct wlr_input_device *device;
+	struct wlr_tablet_tool_tool *tool;
 	uint32_t time_msec;
 	uint32_t button;
 	enum wlr_button_state state;