[PATCH spice-gtk v2] Fix non-tablet non-guest-agent erratic mouse motion

[Marie Stephanie Alesna <istephielicious@xxxxxxxxx>]

We need to compensate the move induced by gdk_device_warp.
We cannot just ignore the next pointer move event as it may include
additional user moves. The fixed issue is most visible over ssh -X.

On Wayland this patch also improves mouse motion as it at least removes
ignoring of each other mouse event.

gdk_display_sync has been removed as I experience no effect of it both before
and after this commit.

Signed-off-by: Marie Stephanie Alesna <istephielicious@xxxxxxxxx>
---
 src/spice-widget-priv.h |  2 ++
 src/spice-widget.c      | 27 ++++++++++++++++++++++-----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/src/spice-widget-priv.h b/src/spice-widget-priv.h
index 1189cbb..728879c 100644
--- a/src/spice-widget-priv.h
+++ b/src/spice-widget-priv.h
@@ -105,6 +105,8 @@ struct _SpiceDisplayPrivate {
     GdkCursor               *show_cursor;
     int                     mouse_last_x;
     int                     mouse_last_y;
+    gdouble                 mouse_delta_x;
+    gdouble                 mouse_delta_y;
     int                     mouse_guest_x;
     int                     mouse_guest_y;
 
diff --git a/src/spice-widget.c b/src/spice-widget.c
index 5365222..3fbb719 100644
--- a/src/spice-widget.c
+++ b/src/spice-widget.c
@@ -28,6 +28,9 @@
 #include <X11/Xlib.h>
 #include <gdk/gdkx.h>
 #endif
+#ifdef GDK_WINDOWING_WAYLAND
+#include <gdk/gdkwayland.h>
+#endif
 #ifdef G_OS_WIN32
 #include <windows.h>
 #include <dinput.h>
@@ -1145,6 +1148,8 @@ static void try_mouse_grab(SpiceDisplay *display)
 
     d->mouse_last_x = -1;
     d->mouse_last_y = -1;
+    d->mouse_delta_x = 0;
+    d->mouse_delta_y = 0;
 }
 
 static void mouse_wrap(SpiceDisplay *display, GdkEventMotion *motion)
@@ -1162,18 +1167,29 @@ static void mouse_wrap(SpiceDisplay *display, GdkEventMotion *motion)
     d->mouse_last_x = -1;
     d->mouse_last_y = -1;
 #else
+
+#ifdef GDK_WINDOWING_WAYLAND
+    // gdk_device_warp has no effect on Wayland and mouse_delta_x/mouse_delta_y
+    // would block any mouse movements there.
+    GdkWindow *window = gtk_widget_get_window(GTK_WIDGET(display));
+    GdkDisplay *gdk_display = gdk_window_get_display(window);
+    if (GDK_IS_WAYLAND_DISPLAY(gdk_display))
+        return;
+#endif
+
     GdkScreen *screen = gtk_widget_get_screen(GTK_WIDGET(display));
     xr = gdk_screen_get_width(screen) / 2;
     yr = gdk_screen_get_height(screen) / 2;
 
     if (xr != (gint)motion->x_root || yr != (gint)motion->y_root) {
         GdkWindow *window = gtk_widget_get_window(GTK_WIDGET(display));
-        /* FIXME: we try our best to ignore that next pointer move event.. */
-        gdk_display_sync(gdk_screen_get_display(screen));
 
+        /* We need to compensate the move induced by gdk_device_warp.
+           We cannot just ignore the next pointer move event as it may include
+           additional user moves. */
         gdk_device_warp(spice_gdk_window_get_pointing_device(window), screen, xr, yr);
-        d->mouse_last_x = -1;
-        d->mouse_last_y = -1;
+        d->mouse_delta_x += xr - motion->x_root;
+        d->mouse_delta_y += yr - motion->y_root;
     }
 #endif
 
@@ -1982,7 +1998,8 @@ static gboolean motion_event(GtkWidget *widget, GdkEventMotion *motion)
         try_keyboard_grab(display);
     }
 
-    transform_input(display, motion->x, motion->y, &x, &y);
+    transform_input(display, motion->x - d->mouse_delta_x,
+                    motion->y - d->mouse_delta_y, &x, &y);
 
     switch (d->mouse_mode) {
     case SPICE_MOUSE_MODE_CLIENT:

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