/****************************************************************************
**
** Copyright (C) 2015 Klaralvdalens Datakonsult AB (KDAB).
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** 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.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** 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
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \example wireframe
    \title Qt 3D: Wireframe QML Example
    \ingroup qt3d-examples-qml

    \brief A Qt 3D QML application that implements a single-pass wireframe
    rendering method.

    \image qt3d-wireframe-rendering.png

    \e {Qt 3D Wireframe Rendering} illustrates how to draw a single entity
    (a trefoil knot) using a custom set of shaders to implement a single-pass
    wireframe rendering method.

    \include examples-run.qdocinc

    \section1 Creating Entities

    The renderer aspect looks for entities that have some geometry, a material,
    and optionally a transformation. These are all specified in the form of
    subclasses of QComponent that have been exported to the QML engine in the
    form of \l Mesh, \l Material, and \l Transform. We use these components to
    create a custom QML item in \e TrefoilKnot.qml.

    We start off by importing the \c {Qt3D 2.0} module that provides the
    \l Entity type and value type helpers, such as Qt.vector3d(). We also import
    the \c {Qt3D.Renderer} module that provides the components and other types
    picked up by the renderer aspect:

    \quotefromfile wireframe/TrefoilKnot.qml
    \skipto import Qt3D
    \printuntil Render

    To use components from other aspects, we would need to import the
    corresponding QML module, too.

    We then use an \l Entity type as the root element of the custom QML type
    exposing some custom properties just as you would with any other type in
    QML:

    \printuntil Material

    In addition to aggregating components, the \l Entity type can be used to
    group child objects together. This is analogous to how the \l Item type is
    used in Qt Quick 2.

    \section1 Specifying Transformations

    We instantiate a \l Transform component and a \l Mesh component. The
    \l Transform component specifies how the renderer should transform the
    geometry when it is drawn with the OpenGL pipeline. We combine an ordered
    set of transformations into a single \l Transform component. This
    information will be automatically available to our shaders through standard
    named uniform variables:

    \skipto Transform
    \printuntil }

    \section1 Loading Dynamic Per-Vertex Data

    The \l Mesh component is very simple. We use its source property to load in
    a static set of geometry (such as vertex positions, normal vectors, and
    texture coordinates) from a file in the Wavefront Obj format. This data was
    exported from the Blender application.

    \printuntil }

    In addition to the \l Mesh element, Qt 3D also enables dynamic generation of
    per-vertex attribute data through C++ hooks that are called by the
    task-based engine.

    \section1 Aggregating Components

    Simply instantiating components is not enough, however. In order for them to
    imbue special behavior on an entity, the entity must aggregate the
    components by means of its components property:

    \quotefromfile wireframe/TrefoilKnot.qml
    \skipto components
    \printuntil ]

    This allows components to be shared between multiple entities very easily.
    In this example, we have components for the transform and mesh that are
    contained within the TrefoilKnot custom type. The final component, of type
    \l Material, is provided by a property of the TrefoilKnot custom type. We
    will later customize the appearance of the entity.

    \section1 Rendering from Cameras

    We use the TrefoilKnot custom type in \e main.qml to draw the trefoil knot
    on the screen.

    We use the same import statements as in \e TrefoilKnot.qml, with the
    addition of a namespaced import for the Qt Quick module that we will
    need for animations:

    \quotefromfile wireframe/main.qml
    \skipto import QtQuick
    \printuntil Render 2.0

    We use an \l Entity type as the root type simply to act as a parent for
    its children. In this sense, the \l Entity type is much like the \l Item
    type:

    \printuntil id

    The RendererSettings component uses the ForwardRenderer type to completely
    configure the renderer without touching any C++ code:

    \printuntil ]

    The BasicCamera type is a trivial wrapper around the built-in \l Camera
    type that represents a virtual camera. It has properties for such things as
    the near and far planes, field of view, aspect ratio, projection type,
    position, and orientation:

    \printuntil }

    The \l Configuration type provides a temporary workaround for having mouse
    control of the camera while the proper implementation that uses aspects and
    components is being completed:

    \printuntil }

    It is trivial to use multiple cameras and choose between them using the
    framegraph for all or part of the scene rendering.

    \section1 Mapping Materials

    Qt 3D has a robust and very flexible \l {Qt 3D Overview#Materials}{material
    system} that allows multiple levels of customization. We use the
    WireframeMaterial custom type to wrap the \l Material type:

    \printuntil diffuse

    We then instantiate the TrefoilKnot type and set the material on it:

    \skipto TrefoilKnot
    \printuntil }

    The Qt 3D engine in conjunction with the renderer aspect now has enough
    information to finally render our mesh using the material we specified.

    \section1 Using Animation Elements

    We use the animation elements provided by Qt Quick 2 to animate the
    properties of the TrefoilKnot and WireframeMaterial types. The properties of
    the components of a type are updated by using the QML property binding
    mechanism:

    \quotefromfile wireframe/main.qml
    \skipto SequentialAnimation
    \printuntil PauseAnimation
    \printuntil }

    The property updates are noticed by the \l{Qt3DCore::}{QNode} base class
    and automatically sent through to the corresponding objects in the renderer
    aspect. The renderer then takes care of translating the property updates
    to new values for uniform variables in the GLSL shader programs.

    Run the example to view the trefoil knot with the width of the wireframe
    lines pulsing. All the heavy lifting is being done by the GPU. The CPU only
    has to run the property animations and to translate the scenegraph and
    framegraph into raw OpenGL calls.

    It is also possible to animate on the GPU via a custom shader program and
    material.
*/