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

/*!
    \example planets-qml
    \title Qt 3D: Planets QML Example
    \ingroup qt3d-examples-qml
    \brief Demonstrates combining Qt 3D rendering and Qt Quick 2 elements.

    \image planets-qml-example.jpg

    \e Planets demonstrates how to implement an application that combines the use of
    Qt 3D rendering with Qt Quick 2D elements. The example shows the eight planets of our Solar
    System with the Sun.

    Planet texture maps are Copyright (c) by James Hastings-Trew
    \l{http://planetpixelemporium.com/planets.html}{http://planetpixelemporium.com/planets.html}
    used with permission.

    The planets are rotating around the Sun based on their orbit at a given time. The rotation
    starts at 2000 Jan 0.0 UT. The planet positions are calculated based on the formulas found here:
    \l {http://www.stjarnhimlen.se/comp/ppcomp.html}{http://www.stjarnhimlen.se/comp/ppcomp.html}
    and \l {http://www.davidcolarusso.com/astro/}{http://www.davidcolarusso.com/astro/}.

    \include examples-run.qdocinc

    \section1 Qt Quick 2D Implementation

    The Qt Quick Implementation in \c {planets-qml/PlanetsMain.qml} of the
    example renders the 3D content using the \c Scene3D type.

    \snippet planets-qml/PlanetsMain.qml 0

    The planet related information is stored into a \c{ListModel}. The selection buttons for the
    planets and the information sheet are created based on the model. The 2D elements, selection
    buttons and sliders, are implemented in \c {planets-qml/PlanetsMain.qml}.

    The selection buttons change the \c{focusedPlanet} property of the \c{mainview}. As the property
    changes, the planet information is updated, and the camera is animated to the new position.

    \snippet planets-qml/PlanetsMain.qml 1

    The camera position and the camera look at point are updated based on values that are animated
    in \c {planets-qml/SolarSystem.qml}, triggered from the
    \c{changePlanetFocus()} function.

    \snippet planets-qml/SolarSystem.qml 0

    The sliders are used to adjust the rotation speed, the planet size, and the viewing distance.
    When a slider value changes, a JavaScript function in \c {planets-qml/SolarSystem.qml}
    is called to adjust the given property. For example, changing the value of
    the \e{Viewing Distance} slider calls the \c{changeCameraDistance()} method.

    \snippet planets-qml/PlanetsMain.qml 2

    \section1 Qt 3D Implementation

    The main part of the implementation, including the movement and rotation maths for the planets,
    is done in \c {planets-qml/SolarSystem.qml}.

    First, a \c Camera, a \c{Light}, and a \c Configuration are added, followed by \c{Effect}s for
    the planet \c{Material}s, and finally the planets themselves. For example, Earth is constructed
    as follows:

    \snippet planets-qml/SolarSystem.qml 1

    Planet data, which is needed for the movement and rotation calculations, among other things, is
    constructed with JavaScript in \c {planets-qml/planets.js} by calling
    \c{loadPlanetData()} as the component completes. Other initializations, such as inserting the
    planets into an array for easier handling, calculating the ring radii for Saturn and Uranus
    rings, and setting the default scale, speed, and camera offset, are done as well:

    \snippet planets-qml/SolarSystem.qml 2

    The scene is animated by calling the \c{animate()} function. That is also the place where the
    time is advanced, and the new positions for all of the planets are calculated. The planets are
    rotated in the \c{positionPlanet()} function based on their axial tilt and their sidereal
    rotation period. Finally, the new camera position is calculated in the \c{updateCamera()}
    function.

    \snippet planets-qml/SolarSystem.qml 3
*/
