[gtk] transform: Add transform_bounds fast path for 2D_AFFINE transforms

[Timm Bäder <baedert src gnome org>]

commit 3bc3e140ddee3f274f0797c10cf7e33dd1b32074
Author: Timm Bäder <mail baedert org>
Date:   Sat Jun 29 09:39:20 2019 +0200

    transform: Add transform_bounds fast path for 2D_AFFINE transforms
    
    E.g. anything involving a scale. This is important when e.g. scrolling
    in the node list in the recorder, which scales every recorded node down
    to fit in the list.

 gsk/gsktransform.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)
---
diff --git a/gsk/gsktransform.c b/gsk/gsktransform.c
index 289e463bb7..9af2ce352b 100644
--- a/gsk/gsktransform.c
+++ b/gsk/gsktransform.c
@@ -1690,11 +1690,26 @@ gsk_transform_transform_bounds (GskTransform          *self,
       }
     break;
 
+    case GSK_TRANSFORM_CATEGORY_2D_AFFINE:
+      {
+        float dx, dy, scale_x, scale_y;
+
+        gsk_transform_to_affine (self, &scale_x, &scale_y, &dx, &dy);
+
+        *out_rect = *rect;
+        out_rect->origin.x *= scale_x;
+        out_rect->origin.y *= scale_y;
+        out_rect->size.width *= scale_x;
+        out_rect->size.height *= scale_y;
+        out_rect->origin.x += dx;
+        out_rect->origin.y += dy;
+      }
+    break;
+
     case GSK_TRANSFORM_CATEGORY_UNKNOWN:
     case GSK_TRANSFORM_CATEGORY_ANY:
     case GSK_TRANSFORM_CATEGORY_3D:
     case GSK_TRANSFORM_CATEGORY_2D:
-    case GSK_TRANSFORM_CATEGORY_2D_AFFINE:
     default:
       {
         graphene_matrix_t mat;