[gtk+] Add a function to get affected area for background

[Matthias Clasen <matthiasc src gnome org>]

commit 5fd7b85d2b37e59e07fba09bedfb9ffea00bef43
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jan 20 09:41:01 2016 -0500

    Add a function to get affected area for background
    
    The new function, gtk_render_background_get_clip answers the
    question: what pixels are affected if I call gtk_render_background ?
    
    The long-term goal is to have APIs that answer this question for
    all rendering primitives.

 docs/reference/gtk/gtk3-sections.txt |    1 +
 gtk/gtkrender.c                      |   33 +++++++++++++++++++++++++++++++++
 gtk/gtkrender.h                      |    9 +++++++++
 3 files changed, 43 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/gtk/gtk3-sections.txt b/docs/reference/gtk/gtk3-sections.txt
index fe439c9..fd7c85a 100644
--- a/docs/reference/gtk/gtk3-sections.txt
+++ b/docs/reference/gtk/gtk3-sections.txt
@@ -6258,6 +6258,7 @@ gtk_border_free
 <SUBSECTION>
 gtk_render_arrow
 gtk_render_background
+gtk_render_background_get_clip
 gtk_render_check
 gtk_render_expander
 gtk_render_extension
diff --git a/gtk/gtkrender.c b/gtk/gtkrender.c
index 6be35a0..42cd58f 100644
--- a/gtk/gtkrender.c
+++ b/gtk/gtkrender.c
@@ -283,6 +283,39 @@ gtk_render_background (GtkStyleContext *context,
 }
 
 /**
+ * gtk_render_background_get_clip:
+ * @context: a #GtkStyleContext
+ * @x: X origin of the rectangle
+ * @y: Y origin of the rectangle
+ * @width: rectangle width
+ * @height: rectangle height
+ * @out_clip: (out): return location for the clip
+ *
+ * Returns the area that will be affected (i.e. drawn to) when
+ * calling gtk_render_background() for the given @context and
+ * rectangle.
+ *
+ * Since: 3.20
+ */
+void
+gtk_render_background_get_clip (GtkStyleContext *context,
+                                gdouble          x,
+                                gdouble          y,
+                                gdouble          width,
+                                gdouble          height,
+                                GdkRectangle    *out_clip)
+{
+  GtkBorder shadow;
+
+  _gtk_css_shadows_value_get_extents (_gtk_style_context_peek_property (context, 
GTK_CSS_PROPERTY_BOX_SHADOW), &shadow);
+
+  out_clip->x = floor (x) - shadow.left;
+  out_clip->y = floor (y) - shadow.top;
+  out_clip->width = ceil (width) + shadow.left + shadow.right;
+  out_clip->height = ceil (height) + shadow.top + shadow.bottom;
+}
+
+/**
  * gtk_render_frame:
  * @context: a #GtkStyleContext
  * @cr: a #cairo_t
diff --git a/gtk/gtkrender.h b/gtk/gtkrender.h
index ea4b84a..81566c5 100644
--- a/gtk/gtkrender.h
+++ b/gtk/gtkrender.h
@@ -59,6 +59,15 @@ void        gtk_render_background  (GtkStyleContext     *context,
                                     gdouble              y,
                                     gdouble              width,
                                     gdouble              height);
+
+GDK_AVAILABLE_IN_3_20
+void        gtk_render_background_get_clip  (GtkStyleContext     *context,
+                                             gdouble              x,
+                                             gdouble              y,
+                                             gdouble              width,
+                                             gdouble              height,
+                                             GdkRectangle        *out_clip);
+
 GDK_AVAILABLE_IN_ALL
 void        gtk_render_frame       (GtkStyleContext     *context,
                                     cairo_t             *cr,