[gnome-shell] dnd: Fix size of actors which don't get allocated their preferred size

[Florian Müllner <fmuellner src gnome org>]

commit 82da73baff4a7ef02d5e62787d7b8b50e5a1ce90
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Tue Jun 9 18:30:12 2020 +0200

    dnd: Fix size of actors which don't get allocated their preferred size
    
    Properly adjust for drag actors which were allocated using a custom
    vfunc_allocate() and might not have gotten allocated their preferred
    size. When DND reparents the actor to the uiGroup, the drag actor will
    get allocated its preferred size, so we also need to take the difference
    between the old allocation size and the preferred size into account
    before reparenting to the uiGroup.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1310

 js/ui/dnd.js | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)
---
diff --git a/js/ui/dnd.js b/js/ui/dnd.js
index 942786d92a..f356c03c7e 100644
--- a/js/ui/dnd.js
+++ b/js/ui/dnd.js
@@ -378,17 +378,27 @@ var _Draggable = class _Draggable {
             this._dragActorHadFixedPos = this._dragActor.fixed_position_set;
             this._dragOrigX = this._dragActor.allocation.x1;
             this._dragOrigY = this._dragActor.allocation.y1;
+            this._dragOrigWidth = this._dragActor.allocation.get_width();
+            this._dragOrigHeight = this._dragActor.allocation.get_height();
             this._dragOrigScale = this._dragActor.scale_x;
 
+            // When the actor gets reparented to the uiGroup, it will be
+            // allocated its preferred size, so use that size instead of the
+            // current allocation size.
+            const [, newAllocatedWidth] = this._dragActor.get_preferred_width(-1);
+            const [, newAllocatedHeight] = this._dragActor.get_preferred_height(-1);
+
+            const transformedAllocation =
+                Shell.util_get_transformed_allocation(this._dragActor);
+
             // Set the actor's scale such that it will keep the same
             // transformed size when it's reparented to the uiGroup
-            let [scaledWidth, scaledHeight] = this.actor.get_transformed_size();
-            this._dragActor.set_scale(scaledWidth / this.actor.width,
-                                      scaledHeight / this.actor.height);
+            this._dragActor.set_scale(
+                transformedAllocation.get_width() / newAllocatedWidth,
+                transformedAllocation.get_height() / newAllocatedHeight);
 
-            let [actorStageX, actorStageY] = this.actor.get_transformed_position();
-            this._dragOffsetX = actorStageX - this._dragStartX;
-            this._dragOffsetY = actorStageY - this._dragStartY;
+            this._dragOffsetX = transformedAllocation.x1 - this._dragStartX;
+            this._dragOffsetY = transformedAllocation.y1 - this._dragStartY;
 
             this._dragOrigParent.remove_actor(this._dragActor);
             Main.uiGroup.add_child(this._dragActor);
@@ -636,9 +646,15 @@ var _Draggable = class _Draggable {
             if (parentWidth != 0)
                 parentScale = parentScaledWidth / parentWidth;
 
+            // Also adjust for the difference in the original actor width
+            // and the width it is now (children of uiGroup always get
+            // allocated their preferred size)
+            const childScaleX =
+                this._dragOrigWidth / this._dragActor.allocation.get_width();
+
             x = parentX + parentScale * this._dragOrigX;
             y = parentY + parentScale * this._dragOrigY;
-            scale = this._dragOrigScale * parentScale;
+            scale = this._dragOrigScale * parentScale * childScaleX;
         } else {
             // Snap back actor to its original stage position
             x = this._snapBackX;