// Copyright (C) 2017 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \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.
 */