[gtk/another-attempt-to-fix-shadertoy: 1/2] snapshot: Don't flip textures

[Matthias Clasen <matthiasc src gnome org>]

commit e6802b9194d165dd2256c80dd832178b1ff6d645
Author: Benjamin Otte <otte redhat com>
Date:   Mon Sep 28 16:09:06 2020 +0200

    snapshot: Don't flip textures
    
    ... or gradients or borders or shadows. Instead, ensure that affines
    have non-negative scale factors. Otherwise add a transform node.
    
    The only place where this check is not necessary is color nodes, but
    special casing them seems not worth it.

 gtk/gtksnapshot.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtksnapshot.c b/gtk/gtksnapshot.c
index 3b7c5173a8..89e4ea9d39 100644
--- a/gtk/gtksnapshot.c
+++ b/gtk/gtksnapshot.c
@@ -697,9 +697,22 @@ gtk_snapshot_ensure_affine (GtkSnapshot *snapshot,
     {
       gtk_snapshot_autopush_transform (snapshot);
       state = gtk_snapshot_get_current_state (snapshot);
+      gsk_transform_to_affine (state->transform, scale_x, scale_y, dx, dy);
+    }
+  else if (gsk_transform_get_category (state->transform) == GSK_TRANSFORM_CATEGORY_2D_AFFINE)
+    {
+      gsk_transform_to_affine (state->transform, scale_x, scale_y, dx, dy);
+      if (*scale_x < 0.0 || *scale_y < 0.0)
+        {
+          gtk_snapshot_autopush_transform (snapshot);
+          state = gtk_snapshot_get_current_state (snapshot);
+          gsk_transform_to_affine (state->transform, scale_x, scale_y, dx, dy);
+        }
+    }
+  else
+    {
+      gsk_transform_to_affine (state->transform, scale_x, scale_y, dx, dy);
     }
-  
-  gsk_transform_to_affine (state->transform, scale_x, scale_y, dx, dy);
 }
 
 static void