[gtkmm] Gdk::Window::create_similar_image_surface(): Return an image surface

[Kjell Ahlstedt <kjellahl src gnome org>]

commit ef7c1a15836500411684240319d1a4f404d5043b
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Mon Mar 5 13:38:31 2018 +0100

    Gdk::Window::create_similar_image_surface(): Return an image surface
    
    * gdk/gdkmm/cairoutils.[cc|h]:
    Make wrap(cairo_surface_t* cobject, bool has_reference) a template function.
    * gdk/src/window.hg: create_similar_image_surface():
    Return a Cairo::RefPtr<Cairo::ImageSurface>, not just a plain
    Cairo::RefPtr<Cairo::Surface>.
    * tools/m4/convert_gdk.m4: Add a conversion for cairo_surface_t*.
    Bug 793572

 gdk/gdkmm/cairoutils.cc |    5 -----
 gdk/gdkmm/cairoutils.h  |    7 ++++++-
 gdk/src/window.hg       |    2 +-
 tools/m4/convert_gdk.m4 |    1 +
 4 files changed, 8 insertions(+), 7 deletions(-)
---
diff --git a/gdk/gdkmm/cairoutils.cc b/gdk/gdkmm/cairoutils.cc
index 3e3cbe9..afcd867 100644
--- a/gdk/gdkmm/cairoutils.cc
+++ b/gdk/gdkmm/cairoutils.cc
@@ -32,11 +32,6 @@ namespace Cairo
   return ::Cairo::make_refptr_for_instance< ::Cairo::Region>(cobject ? new ::Cairo::Region(cobject, 
has_reference) : nullptr);
 }
 
-::Cairo::RefPtr< ::Cairo::Surface> wrap(cairo_surface_t* cobject, bool has_reference)
-{
-  return ::Cairo::make_refptr_for_instance< ::Cairo::Surface>(cobject ? new ::Cairo::Surface(cobject, 
has_reference) : nullptr);
-}
-
 } // namespace Cairo
 
 } // namespace Gdk
diff --git a/gdk/gdkmm/cairoutils.h b/gdk/gdkmm/cairoutils.h
index e10f513..d34a41b 100644
--- a/gdk/gdkmm/cairoutils.h
+++ b/gdk/gdkmm/cairoutils.h
@@ -57,6 +57,7 @@ namespace Cairo
 
 /** Creates a Cairo::RefPtr with a C++ wrapper for the C instance.
  *
+ * @tparam T Cairo::Surface or a subclass of Cairo::Surface.
  * @param cobject The C instance.
  * @param has_reference Whether we already have a reference. Otherwise, the
  *        function will take an extra reference.
@@ -65,7 +66,11 @@ namespace Cairo
  *
  * @newin{3,92}
  */
-::Cairo::RefPtr< ::Cairo::Surface> wrap(cairo_surface_t* cobject, bool has_reference = true);
+template <typename T = ::Cairo::Surface, typename = std::enable_if<std::is_base_of< ::Cairo::Surface, 
T>::value>>
+::Cairo::RefPtr<T> wrap(cairo_surface_t* cobject, bool has_reference = true)
+{
+  return ::Cairo::make_refptr_for_instance<T>(cobject ? new T(cobject, has_reference) : nullptr);
+}
 
 } //namespace Cairo
 } //namespace Gdk
diff --git a/gdk/src/window.hg b/gdk/src/window.hg
index 52ac3b8..42d6257 100644
--- a/gdk/src/window.hg
+++ b/gdk/src/window.hg
@@ -219,7 +219,7 @@ public:
   _WRAP_METHOD(::Cairo::RefPtr< ::Cairo::Surface> create_similar_surface(::Cairo::Content content, int 
width,  int height), gdk_window_create_similar_surface )
 
   #m4 _CONVERSION(`::Cairo::Surface::Format',`cairo_format_t',`(cairo_format_t)($3)')
-    _WRAP_METHOD(::Cairo::RefPtr< ::Cairo::Surface> create_similar_image_surface(::Cairo::Surface::Format 
format, int width, int height, int scale), gdk_window_create_similar_image_surface )
+    _WRAP_METHOD(::Cairo::RefPtr< ::Cairo::ImageSurface> 
create_similar_image_surface(::Cairo::Surface::Format format, int width, int height, int scale), 
gdk_window_create_similar_image_surface )
 
   _WRAP_METHOD(void beep(), gdk_window_beep)
 
diff --git a/tools/m4/convert_gdk.m4 b/tools/m4/convert_gdk.m4
index b0f2d26..342f796 100644
--- a/tools/m4/convert_gdk.m4
+++ b/tools/m4/convert_gdk.m4
@@ -112,6 +112,7 @@ _CONVERSION(`const ::Cairo::RefPtr<const ::Cairo::Region>&',`const cairo_region_
 _CONVERSION(`cairo_region_t*',`::Cairo::RefPtr< ::Cairo::Region>',`Gdk::Cairo::wrap($3)')
 _CONVERSION(`const ::Cairo::RefPtr< ::Cairo::Surface>&',`cairo_surface_t*',`(($3) ? ($3)->cobj() : nullptr)')
 _CONVERSION(`cairo_surface_t*',`::Cairo::RefPtr< ::Cairo::Surface>',`Gdk::Cairo::wrap($3)')
+_CONVERSION(`cairo_surface_t*',`::Cairo::RefPtr< ::Cairo::ImageSurface>',`Gdk::Cairo::wrap< 
::Cairo::ImageSurface>($3)')
 
 _CONVERSION(`const Glib::RefPtr<Cursor>&',`GdkCursor*',__CONVERT_REFPTR_TO_P)
 _CONVERSION(`const Glib::RefPtr<const Cursor>&',`GdkCursor*',__CONVERT_CONST_REFPTR_TO_P)