ui/gtk: enable backend to send multi-touch events

GTK3 provides the infrastructure to receive and process multi-touch
events through the "touch-event" signal and the GdkEventTouch type.
Make use of it to transpose events from the host to the guest.

This allows users of machines with hardware capable of receiving
multi-touch events to run guests that can also receive those events
and interpret them as gestures, when appropriate.

An example of this in action can be seen here:

 https://fosstodon.org/@slp/109545849296546767

Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230526112925.38794-7-slp@redhat.com>

ui/gtk.c

@@ -130,6 +130,13 @@ typedef struct VCChardev VCChardev;
 DECLARE_INSTANCE_CHECKER(VCChardev, VC_CHARDEV,
                          TYPE_CHARDEV_VC)
 
+struct touch_slot {
+    int x;
+    int y;
+    int tracking_id;
+};
+static struct touch_slot touch_slots[INPUT_EVENT_SLOTS_MAX];
+
 bool gtk_use_gl_area;
 
 static void gd_grab_pointer(VirtualConsole *vc, const char *reason);
@@ -1057,6 +1064,82 @@ static gboolean gd_scroll_event(GtkWidget *widget, GdkEventScroll *scroll,
 }
 
 
+static gboolean gd_touch_event(GtkWidget *widget, GdkEventTouch *touch,
+                               void *opaque)
+{
+    VirtualConsole *vc = opaque;
+    struct touch_slot *slot;
+    uint64_t num_slot = GPOINTER_TO_UINT(touch->sequence);
+    bool needs_sync = false;
+    int update;
+    int type = -1;
+    int i;
+
+    if (num_slot >= INPUT_EVENT_SLOTS_MAX) {
+        warn_report("gtk: unexpected touch slot number: % " PRId64" >= %d\n",
+                    num_slot, INPUT_EVENT_SLOTS_MAX);
+        return FALSE;
+    }
+
+    slot = &touch_slots[num_slot];
+    slot->x = touch->x;
+    slot->y = touch->y;
+
+    switch (touch->type) {
+    case GDK_TOUCH_BEGIN:
+        type = INPUT_MULTI_TOUCH_TYPE_BEGIN;
+        slot->tracking_id = num_slot;
+        break;
+    case GDK_TOUCH_UPDATE:
+        type = INPUT_MULTI_TOUCH_TYPE_UPDATE;
+        break;
+    case GDK_TOUCH_END:
+    case GDK_TOUCH_CANCEL:
+        type = INPUT_MULTI_TOUCH_TYPE_END;
+        break;
+    default:
+        warn_report("gtk: unexpected touch event type\n");
+    }
+
+    for (i = 0; i < INPUT_EVENT_SLOTS_MAX; ++i) {
+        if (i == num_slot) {
+            update = type;
+        } else {
+            update = INPUT_MULTI_TOUCH_TYPE_UPDATE;
+        }
+
+        slot = &touch_slots[i];
+
+        if (slot->tracking_id == -1) {
+            continue;
+        }
+
+        if (update == INPUT_MULTI_TOUCH_TYPE_END) {
+            slot->tracking_id = -1;
+            qemu_input_queue_mtt(vc->gfx.dcl.con, update, i, slot->tracking_id);
+            needs_sync = true;
+        } else {
+            qemu_input_queue_mtt(vc->gfx.dcl.con, update, i, slot->tracking_id);
+            qemu_input_queue_btn(vc->gfx.dcl.con, INPUT_BUTTON_TOUCH, true);
+            qemu_input_queue_mtt_abs(vc->gfx.dcl.con,
+                                     INPUT_AXIS_X, (int) slot->x,
+                                     0, surface_width(vc->gfx.ds),
+                                     i, slot->tracking_id);
+            qemu_input_queue_mtt_abs(vc->gfx.dcl.con,
+                                     INPUT_AXIS_Y, (int) slot->y,
+                                     0, surface_height(vc->gfx.ds),
+                                     i, slot->tracking_id);
+            needs_sync = true;
+        }
+    }
+
+    if (needs_sync) {
+        qemu_input_event_sync();
+    }
+
+    return TRUE;
+}
+
 static const guint16 *gd_get_keymap(size_t *maplen)
 {
     GdkDisplay *dpy = gdk_display_get_default();
@@ -1978,6 +2061,8 @@ static void gd_connect_vc_gfx_signals(VirtualConsole *vc)
                          G_CALLBACK(gd_key_event), vc);
         g_signal_connect(vc->gfx.drawing_area, "key-release-event",
                          G_CALLBACK(gd_key_event), vc);
+        g_signal_connect(vc->gfx.drawing_area, "touch-event",
+                         G_CALLBACK(gd_touch_event), vc);
 
         g_signal_connect(vc->gfx.drawing_area, "enter-notify-event",
                          G_CALLBACK(gd_enter_event), vc);
@@ -2087,6 +2172,7 @@ static GSList *gd_vc_gfx_init(GtkDisplayState *s, VirtualConsole *vc,
                               GSList *group, GtkWidget *view_menu)
 {
     bool zoom_to_fit = false;
+    int i;
 
     vc->label = qemu_console_get_label(con);
     vc->s = s;
@@ -2134,6 +2220,7 @@ static GSList *gd_vc_gfx_init(GtkDisplayState *s, VirtualConsole *vc,
                           GDK_BUTTON_PRESS_MASK |
                           GDK_BUTTON_RELEASE_MASK |
                           GDK_BUTTON_MOTION_MASK |
+                          GDK_TOUCH_MASK |
                           GDK_ENTER_NOTIFY_MASK |
                           GDK_LEAVE_NOTIFY_MASK |
                           GDK_SCROLL_MASK |
@@ -2169,6 +2256,11 @@ static GSList *gd_vc_gfx_init(GtkDisplayState *s, VirtualConsole *vc,
         s->free_scale = true;
     }
 
+    for (i = 0; i < INPUT_EVENT_SLOTS_MAX; i++) {
+        struct touch_slot *slot = &touch_slots[i];
+        slot->tracking_id = -1;
+    }
+
     return group;
 }