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/****************************************************************************
**
** Copyright (C) 2020 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
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** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page quick-changes-qt6.html
\title Changes to Qt Quick
\ingroup changes-qt-5-to-6
\brief Migrate Qt Quick to Qt 6.
Qt 6 is a result of the conscious effort to make the framework more
efficient and easy to use.
We try to maintain binary and source compatibility for all the public
APIs in each release. But some changes were inevitable in an effort to
make Qt a better framework.
In this topic we summarize those changes in Qt Quick, and provide
guidance to handle them.
\section1 Changes to Qt Quick QML Types
\section2 Changed Type of font.weight
The type of \c font.weight has been changed to \c int. The pre-defined
weight classes still exist, but it is now possible to use arbitrary integers
to select fonts which do not match any of these weight classes. This ensures
parity with the C++ API, where it has always been possible to express the
font weight as an arbitrary integer.
Most code will be unaffected by this change, except in the case where an
implicit conversion from a string to enum value was used.
\code
font.weight: "Bold"
\endcode
This code will no longer parse correctly and has to be replaced by its
equivalent enum value, as demonstrated below.
\code
font.weight: Font.Bold
\endcode
\section2 FontLoader.name Is Now a Read-Only Property
In Qt 5, the \c name property of FontLoader was writable and would override
the source property of the item when set. This caused some confusion as to
its purpose and could cause undeterministic behavior if there was a race
condition between the setters for the conflicting properties.
This means that code such as the following will no longer work.
\code
FontLoader {
id: fontLoader
name: "Helvetica"
}
Text {
font.family: fontLoader.name
text: "Foobar"
}
\endcode
Instead, use a custom property to store font family names.
\code
property string fontName: "Helvetica"
Text {
font.family: fontName
text: "Foobar"
}
\endcode
\section2 The OpenGLInfo QML Type Is Removed
In Qt 5.8, OpenGLInfo was deprecated and is removed for Qt 6.
Please use GraphicsInfo instead.
\section1 ShaderEffect No Longer Supports Inline GLSL Shader Strings
Just like with \l{QSGMaterial}{custom materials}, the effects are no longer
specified in form of GLSL shader strings. Rather, shaders are expected to be
preprocessed by the tools from the \l{Qt Shader Tools} module, such as the
\c qsb command line tool, thus ensuring the shader assets are usable
regardless of which graphics API (Vulkan, Metal, OpenGL, or Direct 3D) is
used at runtime. ShaderEffect items are expected to reference the resulting
\c{.qsb} files.
\section2 ShaderEffect Source Properties Are Now URLs
The ShaderEffect properties \l{ShaderEffect::vertexShader}{vertexShader} and
\l{ShaderEffect::fragmentShader}{fragmentShader} both have a type of QUrl
now, instead of QByteArray. Their behavior is therefore identical to other
similar properties, such as \l{Image::source}{Image.source}. Existing code
that refers to files via the \c file or \c qrc scheme will continue to work
as-is. In addition, this change allows referring to files with a path
relative to the component's (the .qml file's) location. Specifying the
\c{file:} scheme is therefore optional now.
\section1 Changes to Qt Quick C++ APIs
\section2 Changes to QQuickItem
QQuickItem's geometryChanged() function was renamed to
\l{QQuickItem::}{geometryChange()}.
\section2 Changes to QQuickWidget
QQuickWidget is functional only when the scenegraph is rendering with
OpenGL. It will not be functional when using another graphics API, such as
Vulkan or Metal. Applications relying on QQuickWidget should force the usage
of OpenGL by calling
\c{QQuickWindow::setGraphicsApi(QSGRendererInterface::OpenGLRhi)} in their
main() function.
\section2 Changes to QQuick* APIs
\list
\li Applications wishing to integrate their own set of Vulkan, Metal, or
Direct3D rendering commands should be aware of new QQuickWindow signals in
addition to QQuickWindow::beforeRendering() and afterRendering(). The
existing Qt 5 pattern of connecting to just beforeRendering or
afterRendering is often not sufficient anymore on its own, and will likely
need to be complemented by connecting to additional signals, such as
\l{QQuickWindow::beforeRenderPassRecording()}{beforeRenderPassRecording()}
or \l{QQuickWindow::afterRenderPassRecording()}{afterRenderPassRecording()}.
\li Applications that rely on the QQuickWindow::beforeRendering() or
afterRendering() signals to issue their own set of OpenGL rendering commands
should call QQuickWindow::beginExternalCommands() before, and
QQuickWindow::endExternalCommands() after, the OpenGL calls. This ensures
that state changes made by the application code does not lead to confusion
with regards to the scene graph renderer's own cached state. Note however,
that, just like in Qt 5, changing OpenGL 3.x or 4.x state that is not used
by the Qt Quick renderer can still lead to unexpected issues, so therefore
application are advised to reset any such OpenGL state to the default value
before returning from the slots or lambdas connected to these signals.
\li The existing QQuickWindow::setRenderTarget() overloads, and the
related getters, are removed and replaced by a new function taking a
QQuickRenderTarget. Applications performing redirected rendering in
combination with QQuickRenderControl are now expected to use this new
function to specify the render target in a manner that is not tied to
OpenGL.
\li The QQuickWindow::setSceneGraphBackend() overload taking a
QSGRendererInterface::GraphicsApi argument has been renamed to
\l{QQuickWindow::setGraphicsApi()}{setGraphicsApi()}.
\li The QQuickWindow functions setPersistentOpenGLContext and
isPersistentOpenGLContext are renamed, and are now
QQuickWindow::setPersistentGraphics() and
QQuickWindow::isPersistentGraphics().
\li setClearBeforeRendering() and clearBeforeRendering() have been removed
from QQuickWindow. There is no option for skipping the color buffer clearing
in Qt 6. Calling setClearBeforeRendering() was often necessary in Qt 5 in
combination with underlays, to prevent Qt Quick from clearing the content
rendered into the color buffer. In Qt 6, there is a more robust approach:
connecting to the \c beforeRenderPassRecording() signal,
that is emitted after clearing, but before rendering Qt Quick's content.
\li The QQuickWindow::openglContext() function has been removed. When the
application has ensured the scene graph is using OpenGL for rendering, it
can query the QOpenGLContext from QSGRendererInterface::getResource().
\li The QQuickWindow::openglContextCreated() signal has been removed.
\li The deprecated QQuickWindow::createTextureFromId() function has been
removed. Instead, use the fromNative() function from
QPlatformInterface::QSGOpenGLTexture, QPlatformInterface::QSGVulkanTexture,
QPlatformInterface::QSGD3D11Texture, or QPlatformInterface::QSGMetalTexture.
\li The QQuickFramebufferObject class is available with an unchanged API,
but is only functional when the scenegraph is rendering with OpenGL. It will
not be functional when using another graphics API, such as Vulkan or Metal.
Applications relying on QQuickFramebufferObject should force the usage of
OpenGL by calling
\c{QQuickWindow::setGraphicsApi(QSGRendererInterface::OpenGLRhi)} in their
main() function.
\li QQuickRenderControl has a slightly changed API: grab() is now
removed, use QQuickWindow::grabWindow() instead, where applicable. The
initialize() function no longer takes a QOpenGLContext. Applications are
now also required to call QQuickRenderControl::beginFrame() and
QQuickRenderControl::endFrame() as appropriate. When multisampling is
desired, the new function QQuickRenderControl::setSamples() must be
called to indicate the sample count.
\li Applications wishing to perform Qt Quick rendering in combination
with an existing native graphics device or context object must take the
new QQuickWindow::setGraphicsDevice() function into use as
QQuickRenderControl no longer provides the
\c{initialize(QOpenGLContext*)} function.
\li Setting QQuickPaintedItem and Context2D to \c Framebuffer mode has
no effect. It will behave as if the mode was set to the default Image
mode.
\li The environment variable \c{QSG_NO_DEPTH_BUFFER} is still supported in
Qt 6.0, but its usage is recommended to be replaced by calling
\l{QQuickGraphicsConfiguration::setDepthBufferFor2D()}{setDepthBufferFor2D()}
on a QQuickGraphicsConfiguration that is then associated with the
QQuickWindow.
\endlist
\section1 Changes to QSG* APIs
\list
\li QSGMaterialShader has a changed interface. Implementations should
not rely on OpenGL anymore, and cannot assume that functions, such as
the now-removed updateState(), are called with a QOpenGLContext
current. In the new, data-oriented interface updateState() is replaced
by \l{QSGMaterialShader::updateUniformData()}{updateUniformData()},
\l{QSGMaterialShader::updateSampledImage()}{updateSampledImage()}, and
\l{QSGMaterialShader::updateGraphicsPipelineState()}{updateGraphicsPipelineState()}.
Instead of GLSL shader code provided as strings, shaders are now
expected to be preprocessed by the tools from the Qt Shader Tools
module, such as the \c qsb command line tool, thus ensuring the shader
assets are usable regardless of which graphics API (Vulkan, Metal,
OpenGL, or Direct 3D) is used at run time.
\li QSGEngine has been removed. In the unlikely case of an application
utilizing this class, it is recommended to port to using
QQuickRenderControl instead.
\li QSGAbstractRenderer is no longer public. The usage of this class made
sense only in combination with QSGEngine, and with that class being
removed QSGAbstractRenderer has been moved back to private.
\li The QSGSimpleMaterial convenience class has been
removed. Applications are expected to use the revised, OpenGL-independent
QSGMaterial APIs instead.
\li To access the underlying native texture object for a QSGTexture,
textureId() is no longer available. Instead, use
QSGTexture::platformInterface() with QPlatformInterface::QSGOpenGLTexture,
QPlatformInterface::QSGVulkanTexture, QPlatformInterface::QSGD3D11Texture,
or QPlatformInterface::QSGMetalTexture.
\li Subclasses of QSGImageNode are now required to override new
additional virtuals, such as setAnisotropyLevel() and anisotropyLevel().
\li Subclasses of QSGTexture will likely need to be redesigned. Some of
the OpenGL-specific virtual functions, such as bind() or
updateBindOptions(), are no longer present, while there are new virtuals
that are mandatory to implement, such as
\l{QSGTexture::comparisonKey()}{comparisonKey()}.
\endlist
\section1 Changes to OpenGL Use in Qt Quick
While it will present no breaks for many applications, application
developers should be aware that, OpenGL is not always the default choice
anymore for Qt Quick rendering in Qt 6. Unless the \c software backend is
used, a Qt Quick application could use OpenGL, Vulkan, Metal, or Direct3D 11
at runtime. When no explicit request is made, either via the
\c QSG_RHI_BACKEND environment variable or the
QQuickWindow::setSceneGraphBackend() function, a platform-specific
default is chosen by Qt Quick.
For more information, visit the \l{Qt Quick Scene Graph} and the
\l{Qt Quick Scene Graph Default Renderer} pages.
*/
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