Doc: Add Hello GLES3 example

Task-number: QTBUG-67109
Change-Id: I55135264a63b78502b300de723a25b3f363af58b
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>

examples/opengl/hellogles3/doc/src/hellogles3.qdoc

@@ -0,0 +1,46 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Free Documentation License Usage
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file. Please review the following information to ensure
+** the GNU Free Documentation License version 1.3 requirements
+** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+    \example hellogles3
+    \title Hello GLES3 Example
+    \ingroup examples-widgets-opengl
+
+    \brief The Hello GLES3 example demonstrates easy, cross-platform usage of
+    OpenGL ES 3.0 functions via QOpenGLExtraFunctions in an application that
+    works identically on desktop platforms with OpenGL 3.3 and mobile/embedded
+    devices with OpenGL ES 3.0.
+
+    The code is always the same, with the exception of two places:
+    \list
+      \li The OpenGL context creation has to have a sufficiently high version
+    number for the features that are in use.
+      \li The shader code's version directive is different.
+    \endlist
+
+    \image hellogles3-example.png
+*/

examples/opengl/hellogles3/glwindow.cpp

@@ -243,7 +243,8 @@ void GLWindow::initializeGL()
     f->glEnableVertexAttribArray(0);
     f->glEnableVertexAttribArray(1);
     f->glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), 0);
-    f->glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), reinterpret_cast<void *>(3 * sizeof(GLfloat)));
+    f->glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat),
+                             reinterpret_cast<void *>(3 * sizeof(GLfloat)));
     m_vbo->release();
 
     f->glEnable(GL_DEPTH_TEST);