[gtk] roundedrect: Mke sure shrinking borders works

[Benjamin Otte <otte src gnome org>]

commit 8915d6090040f23e3380d0f019884013ae64f12c
Author: Benjamin Otte <otte redhat com>
Date:   Thu May 2 19:16:16 2019 +0200

    roundedrect: Mke sure shrinking borders works
    
    Previously, when borders were too big - ie when a 100x100 rect had only
    one 100x100 border, like the black part of ◔ - and then shrinking this
    rect by 25px on either side, we'd end up with a 50x50 rect with a 75x75
    border, and that's obviously not correct.

 gsk/gskroundedrect.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)
---
diff --git a/gsk/gskroundedrect.c b/gsk/gskroundedrect.c
index 6498a7c48c..9a389b2eb7 100644
--- a/gsk/gskroundedrect.c
+++ b/gsk/gskroundedrect.c
@@ -197,9 +197,10 @@ gsk_rounded_rect_offset (GskRoundedRect *self,
 }
 
 static void
-border_radius_shrink (graphene_size_t *corner,
-                      double           width,
-                      double           height)
+border_radius_shrink (graphene_size_t       *corner,
+                      double                 width,
+                      double                 height,
+                      const graphene_size_t *max)
 {
   if (corner->width > 0)
     corner->width -= width;
@@ -211,6 +212,11 @@ border_radius_shrink (graphene_size_t *corner,
       corner->width = 0;
       corner->height = 0;
     }
+  else
+    {
+      corner->width = MIN (corner->width, max->width);
+      corner->height = MIN (corner->height, max->height);
+    }
 }
 
 /**
@@ -260,10 +266,10 @@ gsk_rounded_rect_shrink (GskRoundedRect *self,
       self->bounds.size.height -= top + bottom;
     }
 
-  border_radius_shrink (&self->corner[GSK_CORNER_TOP_LEFT], left, top);
-  border_radius_shrink (&self->corner[GSK_CORNER_TOP_RIGHT], right, top);
-  border_radius_shrink (&self->corner[GSK_CORNER_BOTTOM_RIGHT], right, bottom);
-  border_radius_shrink (&self->corner[GSK_CORNER_BOTTOM_LEFT], left, bottom);
+  border_radius_shrink (&self->corner[GSK_CORNER_TOP_LEFT], left, top, &self->bounds.size);
+  border_radius_shrink (&self->corner[GSK_CORNER_TOP_RIGHT], right, top, &self->bounds.size);
+  border_radius_shrink (&self->corner[GSK_CORNER_BOTTOM_RIGHT], right, bottom, &self->bounds.size);
+  border_radius_shrink (&self->corner[GSK_CORNER_BOTTOM_LEFT], left, bottom, &self->bounds.size);
 
   return self;
 }