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/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the QtCanvas3D module of the Qt Toolkit.
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/*!
\example threejs/oneqt
\since QtCanvas3D 1.0
\title One Qt Example
\ingroup qtcanvas3d-examples
\brief Demonstrates combining Qt Quick and three.js rendering.
One Qt example demonstrates how to implement a simple QML 3D control that combines the use
of \c{three.js} library-based Canvas3D rendering with Qt Quick 2D elements. The example shows
a view with various benefits of using Qt with related images picked from
\l {http://qt.io} {http://qt.io}. The images are displayed on the side of a spinning 3D cube
that spins to show the correct image when the tabs at the top of the application are selected.
You can also use swipe gestures to spin the cube to navigate between the tabs. The 3D cube
control has been implemented as a simple QML type that internaly uses \c{three.js} library and
\l{Qt Canvas 3D}.
\image oneqt-example.png
\section1 Main QML File
In \l{threejs/oneqt/oneqt.qml}{oneqt.qml}, we build the 2D content as normal in QML.
Then we add a custom \c {ImageCube} type into the scene behind the text elements.
This custom type, implemented using \c{three.js} library, handles the painting of the 3D
cube.
\snippet threejs/oneqt/oneqt.qml 0
\dots
\note The \c {ImageCube} 3D UI component can be created and anchored just like any other
QML type.
\section1 The Custom 3D QML Control
The \l{threejs/oneqt/ImageCube.qml}{ImageCube.qml} takes six images that it loads
and places to the sides of the cube. In addition, the type has a state that defines which of
these images are visible and a \c {backgroundColor} property that is used when painting the 3D
cube. The \c {angleOffset} property can be used to adjust the cube's direction when displaying
the selected image. In this example the cube component sits on the right edge of the screen so
we twist it slightly to the left so that it appears to be facing the rest of the content.
This angle is also used by the 3D light so that the light always illuminates the selected face
of the cube.
\snippet threejs/oneqt/ImageCube.qml 0
\dots
The custom type defines six states, one for each side of the cube along with the x-, y-, and
z-rotations, that must be set to show the face of the cube corresponding to the state.
\snippet threejs/oneqt/ImageCube.qml 1
\dots
We use \c {RotationAnimation} to animate the transition between angles. It enables us to get
smooth transitions between different cube orientations and to always rotate the cube along the
shortest possible angle distance.
\snippet threejs/oneqt/ImageCube.qml 2
\dots
We call the JavaScript code that uses \c{three.js} to do the rendering of the cube, calling
it on the \c{initializeGL}, \c{paintGL}, and \c{resizeGL} signals.
\snippet threejs/oneqt/ImageCube.qml 3
\section1 The JavaScript Code
The JavaScript side of the implementation,
\l{threejs/oneqt/imagecube.js}{imagecube.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}.
In \l{threejs/oneqt/imagecube.js}{imagecube.js}, we start by creating the camera and
the scene that contains all the rest of the \c{three.js} objects.
\snippet threejs/oneqt/imagecube.js 0
\dots
Then we start the asynchronous loading of the textures and create a material array for the sides
of the cube (note that the cube needs 12 materials as each side consists of two triangles).
\snippet threejs/oneqt/imagecube.js 1
\dots
We then create the needed geometry as \c {BoxGeometry} binding the created materials to the
faces of the cube. We then create a \c {MeshFaceMaterial} from the array of materials.
\snippet threejs/oneqt/imagecube.js 2
Finally we create the cube mesh from the geometry and material, position it, and add it
to the 3D scene.
\snippet threejs/oneqt/imagecube.js 3
Next we create and add some lights to the scene. \c{AmbientLight} defines the surrounding light
amount and the directional light is positioned so that it highlights the face of the cube that
is currently selected.
\snippet threejs/oneqt/imagecube.js 6
Final step in the initialization phase is to create the \c {Canvas3D} renderer and set the
initial size and clear color (color of the background) to the renderer.
\snippet threejs/oneqt/imagecube.js 4
When we need to render the scene in response to the \c{paintGL} signal from Canvas3D, we just
copy the current rotation values from the QML side to the cube mesh in the \c{paintGL()} method.
\snippet threejs/oneqt/imagecube.js 5
For more information on how to use \c {three.js} the documentation is available here:
\l{http://threejs.org/docs/}{three.js/docs}
*/
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