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// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\example proceduraltexture
\ingroup quick3d-examples
\title Qt Quick 3D - Procedural Texture Example
\examplecategory {3D}
\brief Demonstrates how to provide custom texture data from C++ or QML.
\image proceduraltexture-example.jpg
{Gradient cube with procedural texture size and color controls}
This demonstrates the various ways to provide texture data generated dynamically at
runtime instead of loading it from a static asset. For demonstration purposes
this example generates vertical gradient textures from provided start and end
colors.
First we define a C++ class for our texture data. We make it a subclass
of QQuick3DTextureData. This is not strictly necessary, since there are no
virtual functions, but it is much more convenient to have everything in
one class. We define the properties we are going to use, and add
\l QML_NAMED_ELEMENT to make it available from QML:
\snippet proceduraltexture/gradienttexture.h class definition
\dots
We add a function to update the texture. It uses setSize,
and setFormat to configure the texture, and
setTextureData to set the image data:
\snippet proceduraltexture/gradienttexture.cpp updateTexture
The function \c generateTexture creates a QByteArray of the correct size, and
fills it with image data:
\snippet proceduraltexture/gradienttexture.cpp generateTexture
We call \c updateTexture each time a property is changed:
\snippet proceduraltexture/gradienttexture.cpp property
Finally, we can use our new texture from QML:
\snippet proceduraltexture/Main.qml cppTexture
It is also possible to generate the same texture data in QML. In this case we
use the ProceduralTextureData component:
\snippet proceduraltexture/Main.qml qmlTexture
Just like in C++ we fill a QByteArray with image data that reflects the size and
format of the texture. When doing this from QML use the ArrayBuffer type to avoid
unnecessary type conversion.
For the previous two examples, all of the data for the texture is generated on the
CPU side, then uploaded to the GPU for use as texture data. It is also possible to
generate the texture data directly on the GPU. In this case we use subclass
of QQuick3DTextureProviderExtension instead.
\snippet proceduraltexture/gradienttextureprovider.h class definition
QQuick3DTextureProviderExtension based classes define render extensions using the
Qt RHI API. The subclass must return a QSSGRenderExtension based object when
QQuick3DTextureProviderExtension::updateSpatialNode() is called.
\snippet proceduraltexture/gradienttextureprovider.cpp updateSpatialNode
What actually gets rendered is defined by this QSSGRenderExtension subclass:
\snippet proceduraltexture/gradienttextureprovider.cpp GradientTextureProviderNode
By implementing the interfaces of QSSGRenderExtension, the extension can render
the texture data directly on the GPU. The prepareDate implementation makes sure that
the output texture is created with the correct size and format, as well as registers
the output texture as the texture that is being provided.
\snippet proceduraltexture/gradienttextureprovider.cpp prepareData
The prepareRender is where the pipelines are created, and the uniform buffers are
updated.
\snippet proceduraltexture/gradienttextureprovider.cpp prepareRender
The actual rendering for the pass is defined in the render function.
\snippet proceduraltexture/gradienttextureprovider.cpp render
The example uses the texture provider in QML like this:
\snippet proceduraltexture/Main.qml gpuTexture
*/