cppextensionpoints.qdoc

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// Copyright (C) 2017 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
\page qtquick-cppextensionpoints.html
\title C++ Extension Points Provided By Qt Quick
\brief Description of the C++ extension points provided by the Qt Quick module
 
All QML applications can be extended from C++ in order to use additional
functionality implemented in C++ code or to provide a C++ based QML plugin.
This topic of extending QML from C++ is covered in the
\l {Writing QML Extensions with C++} documentation.
 
Additionally, the Qt Quick module provides several extension and integration points for C++
developers, specific to this module. In particular, it allows C++ developers to create and register custom
QQuickItem-derived types which can be rendered by Qt Quick.  It also provides
several scene graph-related classes which allow developers to define their own
rendering primitives.
 
\target user-defined-qquickitem-derived-types
\section1 User-Defined QQuickItem-Derived Types
 
While the Qt Quick module already provides a rich library of visual item types
for use in a QML application, some developers may wish to define their own
item-derived types in C++ and expose them to the QML type system. The easiest
way to do this is to subclass QQuickItem, which is the base type
for all visual types in the Qt Quick module. See the QQuickItem documentation
for more details.
 
\target scene-graph-related-classes
\section1 Scene Graph-Related Classes
 
Qt Quick 2 makes use of a dedicated scene graph based on graphics APIs such as
OpenGL ES, OpenGL, Vulkan, Metal, or Direct 3D for its rendering. Using a scene
graph for graphics rather than the traditional imperative painting systems
(QPainter and similar), means the scene to be rendered can be retained between
frames and the complete set of primitives to render is known before rendering
starts. This opens up for a number of optimizations, such as batching the
OpenGL draw calls to minimize state changes or discarding obscured primitives.
The \l {Qt Quick C++ Classes}{Qt Quick C++ API} provides various classes to
enable custom nodes to be created in C++. See the \l {Qt Quick Scene Graph}
documentation for details.
 
\target pixmap-and-threaded-image-support
\section1 Pixmap and Threaded Image Support
 
While the QML engine allows QML application to load images from filesystem or
network resources, some applications may require the additional option of
loading images from C++ based processes. This can be implemented through the
QQuickImageProvider class, which provides support for pixmap loading and
threaded image requests for QML applications. Any QML application that
requests an image through the special "image:" URL scheme will be directed
to an appropriate image provider to load the image.
 
For more information, see the QQuickImageProvider documentation.
 
*/