[gtk] docs: Some additions to the overview

[Matthias Clasen <matthiasc src gnome org>]

commit 65697e3324047b8fc9347bc50d6067999628c227
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri May 3 04:57:58 2019 +0000

    docs: Some additions to the overview
    
    Mention graphene and gsk.

 docs/reference/gtk/drawing-model.xml |  2 +-
 docs/reference/gtk/overview.xml      | 22 ++++++++++++++++++++--
 2 files changed, 21 insertions(+), 3 deletions(-)
---
diff --git a/docs/reference/gtk/drawing-model.xml b/docs/reference/gtk/drawing-model.xml
index f017de65be..aa0e2ec511 100644
--- a/docs/reference/gtk/drawing-model.xml
+++ b/docs/reference/gtk/drawing-model.xml
@@ -12,7 +12,7 @@
 <refnamediv>
 <refname>The GTK Drawing Model</refname>
 <refpurpose>
-    The GTK drawing model in detail
+    How widgets draw
 </refpurpose>
 </refnamediv>
 
diff --git a/docs/reference/gtk/overview.xml b/docs/reference/gtk/overview.xml
index 5c70182ec9..17b86ab3c8 100644
--- a/docs/reference/gtk/overview.xml
+++ b/docs/reference/gtk/overview.xml
@@ -79,12 +79,30 @@ Use a GdkPixbuf in combination with GtkImage to display images.
 </para></listitem>
 </varlistentry>
 
+<varlistentry>
+<term>graphene</term>
+<listitem><para>
+This is a small library which provides vector and matrix datatypes
+and operations. graphene provides optimized implementations using
+various SIMD instruction sets such as SSE.
+</para></listitem>
+</varlistentry>
+
 <varlistentry>
 <term>GDK</term>
 <listitem><para>
 GDK is the abstraction layer that allows GTK to support multiple
-windowing systems. GDK provides window system facilities on X11, Windows,
-and OS X.
+windowing systems. GDK provides window system facilities on Wayland,
+X11, Windows, and OS X.
+</para></listitem>
+</varlistentry>
+
+<varlistentry>
+<term>GSK</term>
+<listitem><para>
+GSK is a library for creating a scene graph from render nodes,
+and rendering it using different rendering APIs. GSK provides renderers
+for OpenGL, Vulkan and cairo.
 </para></listitem>
 </varlistentry>