Documentation: Add Vulkan section to Qt Gui overview

Add section, external references and link examples.

Task-number: QTBUG-55981
Change-Id: I705f8bacc9d21aff8446ac40b7a172604a18ef85
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/gui/doc/qtgui.qdocconf

@@ -48,6 +48,7 @@ sourcedirs  += .. \
                src/includes
 
 exampledirs += ../../../examples/gui \
+               ../../../examples/vulkan \
                snippets
 
 imagedirs   += images \

src/gui/doc/src/external-resources.qdoc

@@ -60,3 +60,13 @@
     \externalpage https://standards.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html#directory_layout
     \title Icon Theme Specification - Directory Layout
 */
+
+/*!
+    \externalpage https://www.khronos.org/vulkan/
+    \title Vulkan
+*/
+
+/*!
+    \externalpage https://www.lunarg.com/vulkan-sdk/
+    \title LunarG Vulkan SDK
+*/

src/gui/doc/src/qtgui.qdoc

@@ -35,11 +35,11 @@
     applications written with Qt.
 
     The Qt GUI module provides classes for windowing system
-    integration, event handling, OpenGL and OpenGL ES integration, 2D
-    graphics, imaging, fonts and typography. These classes are used
-    internally by Qt's user interface technologies and can also be
-    used directly, for instance to write applications using low-level
-    OpenGL ES graphics APIs.
+    integration, event handling, OpenGL and OpenGL ES integration,
+    Vulkan integration, 2D graphics, imaging, fonts and typography.
+    These classes are used internally by Qt's user interface technologies
+    and can also be used directly, for instance to write applications using
+    low-level OpenGL ES graphics APIs.
 
     To include the definitions of the module's classes, use the
     following directive:
@@ -170,6 +170,31 @@
 
 
 
+    \section1 Vulkan Integration
+
+    Qt 5.10 added support for \l {Vulkan}. This requires
+    the presence of the \l{LunarG Vulkan SDK}.
+
+    On Windows, the SDK sets the environment variable \c {VULKAN_SDK},
+    which will be detected by the \c {configure} script.
+
+    On Android, Vulkan headers were added in API level 24 of the NDK.
+
+    Relevant classes:
+
+    \list
+    \li QVulkanDeviceFunctions
+    \li QVulkanExtension
+    \li QVulkanFunctions
+    \li QVulkanInfoVector
+    \li QVulkanInstance
+    \li QVulkanWindow
+    \li QVulkanWindowRenderer
+    \endlist
+
+    For more information, see the \l{Hello Vulkan Widget Example}
+    and the \l {Hello Vulkan Window Example}.
+
     \section1 Qt GUI Prior to Qt 5.0
 
     Prior to Qt 5.0, the Qt GUI module was the monolithic container