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/*!
    \example threejs/planets
    \since QtCanvas3D 1.0
    \title Planets Example
    \ingroup qtcanvas3d-examples
    \brief Demonstrates combining Qt Quick and three.js rendering.

    The Planets example demonstrates how to implement an application that combines the use of
    three.js library-based Canvas3D rendering with Qt Quick 2D elements. The example shows the eight
    planets of our Solar System with the Sun.

    \image planets-example.jpg

    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/}.

    \section1 Qt Quick Implementation

    The Qt Quick Implementation \l{threejs/planets/planets.qml}{planets.qml} of the example
    renders the 3D content using Canvas3D type. The type calls JavaScript code that uses
    \c{three.js} to initialize, paint, and resize the 3D view.

    \snippet threejs/planets/planets.qml 0

    The planet related information is stored into \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 the QML side.

    The selection buttons change the \c{focusedPlanet} property of the mainview. As the property
    changes the planet information is updated and the camera is animated to the new position. The
    camera position and the camera look at point are updated based on values that are animated on
    QML side.

    \snippet threejs/planets/planets.qml 1

    The sliders are used to adjust the rotation speed, the planet size, and the viewing distance.
    When the slider value changes, JavaScript code is called to adjust the given property. For
    example, changing the value of the "Viewing Distance" slider calls the \c{setCameraDistence()}
    method.

    \snippet threejs/planets/planets.qml 2

    \section1 The JavaScript Code

    The JavaScript side of the implementation, \l{threejs/planets/planets.js}{planets.js},
    is done using a version of \c{three.js} that is ported for \l{Qt Canvas 3D}:
    \l{https://github.com/tronlec/three.js}{three.js}.

    The \c{initializeGL()} method creates the camera and the scene. It also adds the lights to the
    scene and creates the planet meshes. The Canvas3D renderer needs to be created at initialization
    phase too.

    Planet texture maps are Copyright (c) by James Hastings-Trew
    \l{http://planetpixelemporium.com/planets.html}{http://planetpixelemporium.com/planets.html}
    used with permission. To calculate the ring geometry for the planets with rings, the
    \c{_RingGeometry()} method from
    \l{https://github.com/jeromeetienne/threex.planets}{three.xplanets} extension is used.

    The scene is rendered in \c{paintGL()} method. That is also the place where the positions for
    all of the planets are calculated. The planets are rotated based on their axial tilt and their
    sidereal rotation period. In the \c{paintGL()} method the camera position and look at point are
    updated based on the focused planet.

    For more information on how to use \c {three.js} the documentation is available here:
    \l{http://threejs.org/docs/}{three.js/docs}

    \section1 Handling the Mouse Events

    In order to handle the mouse event in JavaScript code the Canvas3D type has to include the
    \c{ControlEventSource} type.

    \snippet threejs/planets/planets.qml 3

    This type is then passed to the JavaScript code on initialization.

    \snippet threejs/planets/planets.qml 4

    On JavaScript code in the \c{initializeGL()} method the \c{eventSource} object is saved to a
    global variable. In this example \c{mouseDown} event is connected to the
    \c{onDocumentMouseDown()} method.

    \snippet threejs/planets/planets.js 5

    Based on the mouse position variables passed to \c{onDocumentMouseDown()} method, it's checked
    if the event takes place on top of a planet or not. The focused planet is changed according to
    the mouse position.

*/
