/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the QtCanvas3D module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL3$
** 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 http://www.qt.io/terms-conditions. For further
** information use the contact form at http://www.qt.io/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 3 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPLv3 included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 3 requirements
** will be met: https://www.gnu.org/licenses/lgpl.html.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 2.0 or later as published by the Free
** Software Foundation and appearing in the file LICENSE.GPL included in
** the packaging of this file. Please review the following information to
** ensure the GNU General Public License version 2.0 requirements will be
** met: http://www.gnu.org/licenses/gpl-2.0.html.
**
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \example canvas3d/textureandlight
    \since QtCanvas3D 1.0
    \title Lit and Textured Cube Example
    \ingroup qtcanvas3d-examples
    \brief A simple cube with texturing and lighting

    The Lit and Textured Cube example goes through the basics of using
    Qt Canvas 3D.

    \image textureandlight-example.png

    \section1 Qt Quick Implementation

    \section2 Creating Canvas3D

    In \l{canvas3d/textureandlight/qml/textureandlight/main.qml}{main.qml}, we add a
    Canvas3D under the root \c Item:

    \snippet canvas3d/textureandlight/qml/textureandlight/main.qml 0
    \dots

    Inside it, we catch the \c initializeGL and \c paintGL signals to forward the
    initialization and rendering calls to the js object:

    \snippet canvas3d/textureandlight/qml/textureandlight/main.qml 1

    \section2 Importing the JavaScript File

    We import the JavaScript file in the QML:

    \snippet canvas3d/textureandlight/qml/textureandlight/main.qml 4

    In the \c initializeGL function of the JavaScript, we initialize the OpenGL
    state. We also create the TextureImage and register handlers for image
    load success and fail signals. If the load succeeds, the OpenGL texture
    is created and filled with pixel data from the loaded image.

    \section1 JavaScript Implementation

    \section2 Matrix Library

    In \l {canvas3d/textureandlight/qml/textureandlight/textureandlight.js}
    {textureandlight.js}, we first include a fast matrix library. Using this
    makes it a lot easier to handle 3D math operations such as matrix
    transformations:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 0

    \section2 initializeGL Function

    Let's take a closer look at the \c initializeGL function. It is called by
    Canvas3D once the render node is ready.

    First of all, we need to get a Context3D from our Canvas3D. We want
    a context that supports depth buffer and antialising:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 1

    Then we initialize the OpenGL state for the context:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 2

    Next, let's take a look into shader initialization in the
    \c initShaders function, which we call in \c{initializeGL}. First we define
    the vertex shader:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 3

    We follow that up by defining a fragment shader:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 4

    Then we need to create the shader program (Canvas3DProgram), attach the shaders
    to it, and then link and use the program:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 5

    And finally, look up and store the vertex attributes and uniform locations:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 6

    After initializing the shader program, we set up the vertex buffer in
    \c initBuffers function. Let's look at the vertex index buffer creation
    as an example:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 7

    Above, first we create the buffer, then bind it and finally insert the
    data into it. Other buffers are all handled in a similar fashion.

    As the final step in \c{initializeGL}, we create a texture image from
    TextureImageFactory, and register handlers for \c imageLoaded and
    \c imageLoadingFailed signals. Once the texture image is successfully
    loaded, we create the actual texture:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 8

    \section2 paintGL Function

    \c paintGL is called by Canvas3D whenever it is ready to receive a new
    frame. Let's go through the steps that are done in each render cycle.

    First we check if canvas has been resized or if pixel ratio has changed,
    and update the projection matrix if necessary:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 9

    Then we clear the render area using the clear color set in \c{initializeGL}:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 10

    Next we reset the model view matrix and apply translation and rotations:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 11

    As we have a lit cube, we invert and transpose the model view matrix to
    be used for lighting calculations:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 12

    And finally we draw the cube:

    \snippet canvas3d/textureandlight/qml/textureandlight/textureandlight.js 13

    \section1 Logging

    Qt Canvas 3D uses Qt's categorized logging feature. This example enables
    all Qt Canvas 3D log output with the code shown below. For more on
    Canvas3D's logging features refer to \l {Qt Canvas 3D Logging}.

    \snippet canvas3d/textureandlight/main.cpp 0
*/
