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++ // 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
++ \examplecategory {3D}
++ \brief Demonstrates providing custom vertex data from C++ and QML.
++ \image customgeometry-example.jpg
++ {Triangle with Qt logo texture demonstrating custom geometry}
++
++ 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++ and QML 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.
++ */