// Copyright (C) 2019 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \example scenegraph/metaltextureimport
    \title Scene Graph - Metal Texture Import
    \examplecategory {Graphics & Multimedia}
    \ingroup qtquickexamples
    \brief Shows how to use a texture created directly with Metal.

    \image metaltextureimport-example.jpg

    The Metal Texture Import example shows how an application can import and
    use a
    \l{https://developer.apple.com/documentation/metal/mtltexture}{MTLTexture}
    in the Qt Quick scene. This provides an alternative to the \l{Scene Graph -
    Metal Under QML}{underlay} or overlay approaches when it comes to integrating
    native Metal rendering. In many cases going through a texture, and
    therefore "flattening" the 3D contents first, is the best option to
    integrate and mix custom 3D contents with the 2D UI elements provided by Qt
    Quick.

    \snippet scenegraph/metaltextureimport/main.qml 1
    \snippet scenegraph/metaltextureimport/main.qml 2

    The application exposes a custom QQuickItem subclass under ther name of
    CustomTextureItem. This is instantiated in QML. The value of the \c t
    property is animated as well.

    \snippet scenegraph/metaltextureimport/metaltextureimport.h 1

    The implementation of our custom item involves overriding
    QQuickItem::updatePaintNode(), as well as functions and slots related to
    geometry changes and cleanup.

    \snippet scenegraph/metaltextureimport/metaltextureimport.mm 1

    We also need a scenegraph node. Instead of deriving directly from QSGNode,
    we can use QSGSimpleTextureNode which gives us some of the functionality
    pre-implemented as a convenience.

    \snippet scenegraph/metaltextureimport/metaltextureimport.mm 2

    The updatePaintNode() function of the item is called on the render thread
    (if there is one), with the main (GUI) thread blocked. Here we create a new
    node if there has not yet been one, and update it. Accessing Qt objects
    living on the main thread is safe here, so sync() will calculate and copy
    the values it needs from QQuickItem or QQuickWindow.

    \snippet scenegraph/metaltextureimport/metaltextureimport.mm 3

    The node does not merely rely on the typical QQuickItem - QSGNode
    update sequence, it connects to QQuickWindow::beforeRendering() as
    well. That is where the contents of the Metal texture will be updated by
    encoding a full render pass, targeting the texture, on the Qt Quicks
    scenegraph's command buffer. beforeRendering() is the right place for this,
    because the signal is emitted before Qt Quick starts to encode its own
    rendering commands. Choosing QQuickWindow::beforeRenderPassRecording()
    instead would be an error in this exanple.

    \snippet scenegraph/metaltextureimport/metaltextureimport.mm 4
    \snippet scenegraph/metaltextureimport/metaltextureimport.mm 5

    After copying the values we need, sync() also performs some graphics
    resource initialization. The MTLDevice is queried from the scenegraph. Once
    a MTLTexture is available, a QSGTexture wrapping (not owning) it is created
    via QQuickWindow::createTextureFromNativeObject(). This function is a
    modern equivalent to QQuickWindow::createTextureFromId() that is not tied
    to OpenGL. Finally, the QSGTexture is associated with the underlying
    materials by calling the base class' setTexture() function.

    \snippet scenegraph/metaltextureimport/metaltextureimport.mm 6

    render(), the slot connected to beforeRendering(), encodes the rendering
    commands using the buffers and pipeline state objects created in sync().

  */
