Expose GLES 3.0 and 3.1 functions

Using the approach we already do for some GLES 3.0 functions we can provide a cross-platform,
cross-GL-GLES wrapper for ES 3.0 and 3.1 functions too.

Applications only have to take extra care about the version requests (context version
and version directives in shader code), the rest of their code can stay the same across
desktop/mobile/embedded, even when ES 3 functions are used.

The new functions are placed to a new subclass which is placed between QOpenGLFunctions
and the internal QOpenGLExtensions. This is necessary because, unlike with QOpenGLFunctions,
there is no guarantee that these functions are always available in all configurations.

When running on desktop OpenGL, we resolve as usual. If the OpenGL version contains the
function in question, either in core or as an extension, it will all just work. This is
handy because it does not rely on 4.x extensions like GL_ARB_ESx_compatibility, and so
ES 3.0 functions will be functional on OpenGL 3.x systems too by just setting a 3.x version
number in the QSurfaceFormat.

We will no longer qFatal on broken systems where the driver returns a 3.0 or 3.1 context without
the corresponding functions present. Instead, we show a warning and gracefully fall back to
resolving as usual, via eglGetProcAddress or similar. For functions that are available in ES2 as
an extension this may just work fine.

Added also an example that runs identically both with OpenGL and OpenGL ES 3 and utilizes some
ES 3.0 features like instanced drawing.

[ChangeLog] Added QOpenGLExtraFunctions providing OpenGL ES 3.0 and 3.1 function wrappers in
a cross-platform manner.

Task-number: QTBUG-46161
Change-Id: I9f929eb61946c35c415b178c4d6ab2c1c958684e
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>

1 files changed, 78 insertions, 0 deletions

diff --git a/examples/opengl/hellogles3/main.cpp b/examples/opengl/hellogles3/main.cpp
new file mode 100644
index 0000000000..3125623395
--- /dev/null
+++ b/examples/opengl/hellogles3/main.cpp
@@ -0,0 +1,78 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QApplication>
+#include <QSurfaceFormat>
+#include <QOpenGLContext>
+
+#include "mainwindow.h"
+
+// This 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: (1) the OpenGL context
+// creation has to have a sufficiently high version number for the features that are in
+// use, and (2) the shader code's version directive is different.
+
+int main(int argc, char *argv[])
+{
+    QSurfaceFormat fmt;
+    fmt.setDepthBufferSize(24);
+
+    // Request OpenGL 3.3 compatibility or OpenGL ES 3.0.
+    if (QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL) {
+        qDebug("Requesting 3.3 compatibility context");
+        fmt.setVersion(3, 3);
+        fmt.setProfile(QSurfaceFormat::CompatibilityProfile);
+    } else {
+        qDebug("Requesting 3.0 context");
+        fmt.setVersion(3, 0);
+    }
+
+    QSurfaceFormat::setDefaultFormat(fmt);
+
+    QApplication app(argc, argv);
+
+    MainWindow mainWindow;
+    mainWindow.showMaximized();
+
+    return app.exec();
+}