[gtk+] Be more careful with floating point divisions

[Matthias Clasen <matthiasc src gnome org>]

commit 3f56c530b3b5c77f2b9194c479afd1cdd25e9a42
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jan 8 13:17:58 2016 -0500

    Be more careful with floating point divisions
    
    The assumption that MIN() takes care of all infinities here
    turns out to be wrong. We were getting inf and -nan for some
    combinations of 0 width/height and corners, leading to invalid
    matrices and cairo errors.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=759668

 gtk/gtkroundedbox.c |   25 ++++++++++++++++---------
 1 files changed, 16 insertions(+), 9 deletions(-)
---
diff --git a/gtk/gtkroundedbox.c b/gtk/gtkroundedbox.c
index 3d2befe..b63b7d5 100644
--- a/gtk/gtkroundedbox.c
+++ b/gtk/gtkroundedbox.c
@@ -56,16 +56,23 @@ static void
 gtk_rounded_box_clamp_border_radius (GtkRoundedBox *box)
 {
   gdouble factor = 1.0;
+  gdouble corners;
 
-  /* note: division by zero leads to +INF, which is > factor, so will be ignored */
-  factor = MIN (factor, box->box.width / (box->corner[GTK_CSS_TOP_LEFT].horizontal +
-                                          box->corner[GTK_CSS_TOP_RIGHT].horizontal));
-  factor = MIN (factor, box->box.height / (box->corner[GTK_CSS_TOP_RIGHT].vertical +
-                                           box->corner[GTK_CSS_BOTTOM_RIGHT].vertical));
-  factor = MIN (factor, box->box.width / (box->corner[GTK_CSS_BOTTOM_RIGHT].horizontal +
-                                          box->corner[GTK_CSS_BOTTOM_LEFT].horizontal));
-  factor = MIN (factor, box->box.height / (box->corner[GTK_CSS_TOP_LEFT].vertical +
-                                           box->corner[GTK_CSS_BOTTOM_LEFT].vertical));
+  corners = box->corner[GTK_CSS_TOP_LEFT].horizontal + box->corner[GTK_CSS_TOP_RIGHT].horizontal;
+  if (corners != 0)
+    factor = MIN (factor, box->box.width / corners);
+
+  corners = box->corner[GTK_CSS_TOP_RIGHT].vertical + box->corner[GTK_CSS_BOTTOM_RIGHT].vertical;
+  if (corners != 0)
+    factor = MIN (factor, box->box.height / corners);
+
+  corners = box->corner[GTK_CSS_BOTTOM_RIGHT].horizontal + box->corner[GTK_CSS_BOTTOM_LEFT].horizontal;
+  if (corners != 0)
+    factor = MIN (factor, box->box.width / corners);
+
+  corners = box->corner[GTK_CSS_TOP_LEFT].vertical + box->corner[GTK_CSS_BOTTOM_LEFT].vertical;
+  if (corners != 0)
+    factor = MIN (factor, box->box.height / corners);
 
   box->corner[GTK_CSS_TOP_LEFT].horizontal *= factor;
   box->corner[GTK_CSS_TOP_LEFT].vertical *= factor;