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/****************************************************************************
**
** Copyright (C) 2017 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
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** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
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** 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
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** $QT_END_LICENSE$
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****************************************************************************/
/*!
\example scenegraph/custommaterial
\title Scene Graph - Custom Material
\ingroup qtquickexamples
\brief Shows how to implement a custom material in the Qt Quick Scene Graph.
The custom material example shows how to implement an item that is rendered
using a material with a custom vertex and fragment shader.
\image custom-material-example.jpg
\section1 Shader and material
The main functionality is in the fragment shader
\quotefile scenegraph/custommaterial/shaders/mandelbrot.frag
The fragment and vertex shaders are combined into a \l QSGMaterialShader subclass.
\snippet scenegraph/custommaterial/customitem.cpp 2
A QSGMaterial subclass encapsulates the shader together with the render state. In
this example, we add state information corresponding to the shader uniforms. The
material is responsible for creating the shader by reimplementing
\l QSGMaterial::createShader().
\snippet scenegraph/custommaterial/customitem.cpp 1
To update the uniform data, we reimplement \l QSGMaterialShader::updateUniformData().
\snippet scenegraph/custommaterial/customitem.cpp 3
\section1 Item and node
We create a custom item to show off our new material:
\snippet scenegraph/custommaterial/customitem.h 1
The CustomItem declaration adds three
properties corresponding to the uniforms that we want to expose to QML.
\snippet scenegraph/custommaterial/customitem.h 2
As with every custom Qt Quick item, the implementation is split in two:
in addition to \c CustomItem, which lives in the GUI thread, we create
a \l QSGNode subclass that lives in the render thread.
\snippet scenegraph/custommaterial/customitem.cpp 4
The node owns an instance of the material, and has logic to update
the material's state. The item maintains the corresponding QML properties.
It needs to duplicate the information from the material since the item and
material live on different threads.
\snippet scenegraph/custommaterial/customitem.cpp 5
The information is copied from the item to the scene graph in a
reimplementation of \l QQuickItem::updatePaintNode(). The two threads
are at a synchronization point when the function is called, so it is safe
to access both classes.
\snippet scenegraph/custommaterial/customitem.cpp 6
\section1 The rest of the example
The application is a straightforward QML application, with a
QGuiApplication and a QQuickView that we pass a .qml file.
In the QML file, we create the
customitem which we anchor to fill the root.
\snippet scenegraph/custommaterial/main.qml 1
To make the example a bit more interesting we add an animation to
change the zoom level and iteration limit. The center stays constant.
*/
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