[gtk/wip/otte/canvas: 2/2] canvas: scale(-1) the widgets when allocation size is negative

[Benjamin Otte <otte src gnome org>]

commit 9ae808c14785be4ae09fb305966f77bfcdede0de
Author: Benjamin Otte <otte redhat com>
Date:   Tue Jul 5 07:30:51 2022 +0200

    canvas: scale(-1) the widgets when allocation size is negative
    
    Just flip the widgets, because hey, that makes planarity work!

 gtk/gtkcanvasitem.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)
---
diff --git a/gtk/gtkcanvasitem.c b/gtk/gtkcanvasitem.c
index e19c9017e1..c396bc5f0d 100644
--- a/gtk/gtkcanvasitem.c
+++ b/gtk/gtkcanvasitem.c
@@ -271,20 +271,28 @@ gtk_canvas_item_allocate_widget (GtkCanvasItem *self,
                                  float          dy)
 {
   graphene_rect_t allocation;
+  GskTransform *transform;
 
   if (self->widget == NULL)
     return;
 
   gtk_canvas_box_to_rect (&self->allocation, &allocation);
-  graphene_rect_normalize (&allocation);
-
-  gtk_widget_size_allocate (self->widget,
-                            &(GtkAllocation) {
-                              allocation.origin.x - dx,
-                              allocation.origin.y - dy,
-                              allocation.size.width,
-                              allocation.size.height
-                            }, -1);
+
+  transform = gsk_transform_translate (NULL,
+                                       &GRAPHENE_POINT_INIT (
+                                         allocation.origin.x - dx
+                                         + (signbit (self->allocation.size.width) ? allocation.size.width : 
0),
+                                         allocation.origin.y - dy
+                                         + (signbit (self->allocation.size.height) ? allocation.size.height 
: 0)));
+  transform = gsk_transform_scale (transform,
+                                   signbit (self->allocation.size.width) ? -1 : 1,
+                                   signbit (self->allocation.size.height) ? -1 : 1);
+
+  gtk_widget_allocate (self->widget,
+                       allocation.size.width,
+                       allocation.size.height,
+                       -1,
+                       transform);
 }
 
 gboolean