Scene3D: introduce compositingMode (FBO or Underlay)

The default compositing mode is FBO.

One of the problematic aspects of Scene3D is its round trip
through a FBO, which is moderately expensive on low-end hardware,
although it makes it a fully fledged Qt Quick 2 item. If one
wants MSAA then things are even worse, as an intermediate MS'ed
FBO is needed, then resolving into the final one, whose color
texture is then sampled.

However, there's a significant use case for which these FBOs
can be avoided, and that's the case of a 3D scene "below" other
QQ2 content. In this setup, Qt3D can simply render to the
screen, driven by QQ2; then QQ2 can draw on top.

(It's the typical "underlay" scenario.) This can be enabled by setting
the compositing mode to Underlay

[ChangeLog] Scene3D add compositingMode property. Allows underlay rendering.

Task-number: QTBUG-74977
Change-Id: I1ec5f5d60eab45835dbdb2596a7bf1b2ac3624e0
Reviewed-by: Mike Krus <mike.krus@kdab.com>

1 files changed, 70 insertions, 0 deletions

diff --git a/examples/qt3d/controlsunderlay/main.cpp b/examples/qt3d/controlsunderlay/main.cpp
new file mode 100644
index 000000000..cb3928a51
--- /dev/null
+++ b/examples/qt3d/controlsunderlay/main.cpp
@@ -0,0 +1,70 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Qt3D module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, 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 <QGuiApplication>
+#include <QQuickView>
+
+int main(int argc, char **argv)
+{
+    QSurfaceFormat format;
+    format.setSamples(4);
+    QSurfaceFormat::setDefaultFormat(format);
+
+    QGuiApplication app(argc, argv);
+
+    QQuickView view;
+
+    view.resize(520, 500);
+    view.setResizeMode(QQuickView::SizeRootObjectToView);
+    view.setSource(QUrl("qrc:/main.qml"));
+    view.show();
+
+    return app.exec();
+}