[mutter] kms/plane-assignment: Add API to set cursor hotspot metadata

[Carlos Garnacho <carlosg src gnome org>]

commit 55cf1c1496a51ad221901e6f6aa4b8a21adcbf54
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu Mar 19 09:01:03 2020 +0100

    kms/plane-assignment: Add API to set cursor hotspot metadata
    
    The transactional KMS API has been modelled after atomic KMS. Atomic KMS
    currently doesn't support forwarding cursor hotspot metadata, thus it
    was left out of the transactional KMS API having the user set the simply
    create a plane assigment with the cursor sprite assigned to a cursor
    plane using regular coordinates.
    
    This, however, proved to be inadequate for virtual machines using
    "seamless mouse mode" where they rely on the cursor position to
    correspond to the actual cursor position of the virtual machine, not the
    cursor plane. In effect, this caused cursor positions to look "shifted".
    
    Fix this by adding back the hotspot metadata, right now as a optional
    field to the plane assignment. In the legacy KMS implementation, this is
    translated into drmModeSetCursor2() just as before, while still falling
    back to drmModeSetCursor() with the plane coordinates, if either there
    was no hotspot set, or if drmModeSetCursor2() failed.
    
    Eventually, the atomic KMS API will learn about hotspots, but when
    adding our own atomic KMS backend to the transacitonal KMS API, we must
    until then still fall back to legacy KMS for virtual machines.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1136

 src/backends/native/meta-kms-impl-simple.c    | 21 +++++++++++++++++----
 src/backends/native/meta-kms-update-private.h |  6 ++++++
 src/backends/native/meta-kms-update.c         | 10 ++++++++++
 src/backends/native/meta-kms-update.h         |  4 ++++
 4 files changed, 37 insertions(+), 4 deletions(-)
---
diff --git a/src/backends/native/meta-kms-impl-simple.c b/src/backends/native/meta-kms-impl-simple.c
index ddc31b938..e50b1c888 100644
--- a/src/backends/native/meta-kms-impl-simple.c
+++ b/src/backends/native/meta-kms-impl-simple.c
@@ -771,14 +771,27 @@ process_cursor_plane_assignment (MetaKmsImpl             *impl,
   if (!(plane_assignment->flags & META_KMS_ASSIGN_PLANE_FLAG_FB_UNCHANGED))
     {
       int width, height;
-      int ret;
+      int ret = -1;
 
       width = meta_fixed_16_to_int (plane_assignment->dst_rect.width);
       height = meta_fixed_16_to_int (plane_assignment->dst_rect.height);
 
-      ret = drmModeSetCursor (fd, meta_kms_crtc_get_id (plane_assignment->crtc),
-                              plane_assignment->fb_id,
-                              width, height);
+      if (plane_assignment->cursor_hotspot.is_valid)
+        {
+          ret = drmModeSetCursor2 (fd, meta_kms_crtc_get_id (plane_assignment->crtc),
+                                   plane_assignment->fb_id,
+                                   width, height,
+                                   plane_assignment->cursor_hotspot.x,
+                                   plane_assignment->cursor_hotspot.y);
+        }
+
+      if (ret != 0)
+        {
+          ret = drmModeSetCursor (fd, meta_kms_crtc_get_id (plane_assignment->crtc),
+                                  plane_assignment->fb_id,
+                                  width, height);
+        }
+
       if (ret != 0)
         {
           g_set_error (error, G_IO_ERROR, g_io_error_from_errno (-ret),
diff --git a/src/backends/native/meta-kms-update-private.h b/src/backends/native/meta-kms-update-private.h
index 91a1de6dc..4d4d4a276 100644
--- a/src/backends/native/meta-kms-update-private.h
+++ b/src/backends/native/meta-kms-update-private.h
@@ -51,6 +51,12 @@ typedef struct _MetaKmsPlaneAssignment
   MetaKmsAssignPlaneFlag flags;
 
   GList *plane_properties;
+
+  struct {
+    gboolean is_valid;
+    int x;
+    int y;
+  } cursor_hotspot;
 } MetaKmsPlaneAssignment;
 
 typedef struct _MetaKmsModeSet
diff --git a/src/backends/native/meta-kms-update.c b/src/backends/native/meta-kms-update.c
index 0371782b7..5ace83021 100644
--- a/src/backends/native/meta-kms-update.c
+++ b/src/backends/native/meta-kms-update.c
@@ -340,6 +340,16 @@ meta_kms_plane_assignment_set_plane_property (MetaKmsPlaneAssignment *plane_assi
     g_list_prepend (plane_assignment->plane_properties, plane_prop);
 }
 
+void
+meta_kms_plane_assignment_set_cursor_hotspot (MetaKmsPlaneAssignment *plane_assignment,
+                                              int                     x,
+                                              int                     y)
+{
+  plane_assignment->cursor_hotspot.is_valid = TRUE;
+  plane_assignment->cursor_hotspot.x = x;
+  plane_assignment->cursor_hotspot.y = y;
+}
+
 MetaKmsPlaneAssignment *
 meta_kms_update_get_primary_plane_assignment (MetaKmsUpdate *update,
                                               MetaKmsCrtc   *crtc)
diff --git a/src/backends/native/meta-kms-update.h b/src/backends/native/meta-kms-update.h
index cd1822e4a..13dff16dd 100644
--- a/src/backends/native/meta-kms-update.h
+++ b/src/backends/native/meta-kms-update.h
@@ -108,6 +108,10 @@ void meta_kms_update_custom_page_flip (MetaKmsUpdate                 *update,
                                        MetaKmsCustomPageFlipFunc      custom_page_flip_func,
                                        gpointer                       custom_page_flip_user_data);
 
+void meta_kms_plane_assignment_set_cursor_hotspot (MetaKmsPlaneAssignment *plane_assignment,
+                                                   int                     x,
+                                                   int                     y);
+
 static inline MetaFixed16
 meta_fixed_16_from_int (int16_t d)
 {