// Copyright (C) 2019 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \example customgeometry
    \ingroup quick3d-examples
    \title Qt Quick 3D - Custom Geometry Example
    \brief Demonstrates providing custom vertex data from C++.
    \image customgeometry-example.jpg

    This example makes use of QQuick3DGeometry and \l{Model::geometry}{the
    geometry property} of Model to render a mesh with vertex, normal, and
    texture coordinates specified from C++ instead of a pre-baked asset.

    In addition, the \l GridGeometry is also demonstrated. GridGeometry is a
    built-in QQuick3DGeometry implementation that provides a mesh with line
    primitives suitable for displaying a grid.

    The focus on this example will be on the code that provides the custom
    geometry, so let's first have a look at the \c ExampleTriangleGeometry C++
    header file:

    \snippet customgeometry/examplegeometry.h triangle geometry

    The most important thing to notice is that our \c ExampleTriangleGeometry
    class inherits from QQuick3DGeometry and that we call the \c
    QML_NAMED_ELEMENT(ExampleTriangleGeometry) macro, making our class
    accessible in QML. There are also a few properties defined through the \c
    Q_PROPERTY macro which are automatically exposed in our QML object. Now,
    let's look at the QML Model:

    \snippet customgeometry/main.qml model triangle

    Note that we specify the \c geometry property to use our \c
    ExampleTriangleGeometry class, with the relevant properties specified. This
    is all that is needed on the QML side to use a custom geometry.

    Now, lets look at the other important part of the C++ code, namely the \c
    updateData() method. This method creates and uploads the data for our custom
    geometry whenever a \c ExampleTriangleGeometry class is created or any of
    its QML properties are updated.

    \snippet customgeometry/examplegeometry.cpp update data

    The method starts by calling \c clear() to clear all previously uploaded
    data. It then computes the stride for the vertices, taking into account the
    presence of normals and uv coordinates. Then a byte array is created to hold
    the vertex buffer, which is then filled with vertices for a single triangle
    with corners in (-1, -1, 0), (1, -1, 0) and (0, 1, 0).

    Then the vertex data is uploaded and the stride is set by calling
    \c setVertexData() and \c setStride(). The bounds of the geometry
    is set by calling \c setBounds. Although not used in this example
    setting the bounds is needed for shadows to work. Then the primitive
    type is set by calling \c setPrimitiveType(). Lastly, we specify how
    the attributes for position, normal and uv coords are laid out in
    memory in the previously uploaded buffer by calling \c addAttribute()
    for each attribute.
*/
