diff options
Diffstat (limited to 'src/quick/doc/src/concepts/visualcanvas/adaptations.qdoc')
| -rw-r--r-- | src/quick/doc/src/concepts/visualcanvas/adaptations.qdoc | 354 |
1 files changed, 53 insertions, 301 deletions
diff --git a/src/quick/doc/src/concepts/visualcanvas/adaptations.qdoc b/src/quick/doc/src/concepts/visualcanvas/adaptations.qdoc index 8edc5cb0b6..d4c0c0eb2b 100644 --- a/src/quick/doc/src/concepts/visualcanvas/adaptations.qdoc +++ b/src/quick/doc/src/concepts/visualcanvas/adaptations.qdoc @@ -1,29 +1,5 @@ -/**************************************************************************** -** -** Copyright (C) 2017 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 -** accordance with the commercial license agreement provided with the -** Software or, alternatively, in accordance with the terms contained in -** a written agreement between you and The Qt Company. For licensing terms -** and conditions see https://www.qt.io/terms-conditions. For further -** 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. -** $QT_END_LICENSE$ -** -****************************************************************************/ +// Copyright (C) 2017 The Qt Company Ltd. +// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only /*! \title Scene Graph Adaptations @@ -31,15 +7,38 @@ \section1 Scene Graph Adaptations in Qt Quick -Originally, Qt Quick always relied on OpenGL (OpenGL ES 2.0 or OpenGL 2.0) to parse the scene graph -and render the results to a render target. From Qt 5.8 onwards, Qt Quick also supports rendering in -software and with Direct3D 12. +In Qt 5.0, Qt Quick always relied on OpenGL (OpenGL ES 2.0 or OpenGL 2.0) to +parse the scene graph and render the results to a render target. + +From Qt 5.8 onwards, Qt Quick also supports rendering in software, and with +OpenVG. This is realized by having additional scene graph adaptations, either +in form of plugins (openvg) or built-in to the Qt Quick library +(software). The default adaptation continues to rely directly on OpenGL. + +From Qt 5.14 onwards, the default adaptation gains the option of rendering via +a graphics abstraction layer, the Qt Rendering Hardware Interface (RHI), +provided by the \l [QtGui]{Qt GUI} module. When enabled, no direct OpenGL calls are made. +Rather, the scene graph renders by using the APIs provided by the abstraction +layer, which is then translated into OpenGL, Vulkan, Metal, or Direct 3D calls. +Shader handling is also unified by writing shader code once, compiling to +\l{https://www.khronos.org/spir/}{SPIR-V}, and then translating to the language +appropriate for the various graphics APIs. + +Starting with Qt 6.0, the RHI-based rendering model is the default, and there is +no option to fall back to directly using OpenGL. \target Switching Between the Adaptation Used by the Application \section1 Switch Between Adaptations in Your Application -The default rendering backend is still OpenGL, but in Qt builds with OpenGL support disabled, the -default is the software renderer. You can override this in one of two ways: +Unlike \c software, the RHI-based renderer is not an additional adaptation, and +is always built-in. As of Qt 6.0 it is always enabled. On platforms where +multiple graphics APIs are available, the scenegraph makes a platform-specific +choice. If this is not desired, applications can force a specified graphics API +by setting the environment variable \c{QSG_RHI_BACKEND} or via \l +QQuickWindow::setGraphicsApi() in combination with \l +QSGRendererInterface::GraphicsApi. + +Switching to a different adaptation can be achieved in two ways: \list \li Use an environment variable - Set the \c{QT_QUICK_BACKEND} or the legacy @@ -51,11 +50,10 @@ default is the software renderer. You can override this in one of two ways: The following backends are supported: \list - \li OpenGL - Request with the \c{""} string or the QSGRendererInterface::OpenGL enum value. + \li Default - Request with the \c{"rhi"} string or a QSGRendererInterface::GraphicsApi enum value + different than the ones listed below. \li Software - Request with the \c{"software"} string or the QSGRendererInterface::Software enum value. - \li Direct3D 12 - Request with the \c{"d3d12"} string or the QSGRendererInterface::Direct3D12 - enum value. \li OpenVG - Request with the \c{"openvg"} string or the QSGRendererInterface::OpenVG enum value. \endlist @@ -64,16 +62,21 @@ To find out which backend is in use, you can enable basic scene graph informatio \c{QSG_INFO} environment variable or the \c{qt.scenegraph.general} logging category. This results in some information being printed onto the debug output, during application startup. -\note Typically, adaptations other than OpenGL come with a set of limitations as they are unlikely - to provide a feature set that's 100% compatible with OpenGL. However, these adaptations may - provide their own specific advantages in certain areas. For more information on the various - adaptations, refer to the sections below. +\note In Qt builds with both OpenGL and Vulkan disabled, the default adaptation +is \c software. This does not apply to Windows or \macos however, because these +platforms always have Direct 3D or Metal support, respectively, enabled. + +\note Typically, adaptations other than the default one come with a set of +limitations as they are unlikely to provide a feature set that's 100% +compatible with OpenGL. However, these adaptations may provide their own +specific advantages in certain areas. For more information on the various +adaptations, refer to the sections below. -\section1 OpenGL ES 2.0 and OpenGL 2.0 Adaptation +\section1 Default Adaptation -The OpenGL adaptation is the default adaptation, which is capable of providing the full Qt Quick 2 -feature set. For more details, see -\l{qtquick-visualcanvas-scenegraph-renderer.html}{OpenGL Adaptation}. +When using OpenGL directly, the default adaptation is capable of providing the +full Qt Quick 2 feature set. For more details, see +\l{qtquick-visualcanvas-scenegraph-renderer.html}{Default Adaptation}. \section1 Software Adaptation @@ -81,12 +84,6 @@ The Software adaptation is an alternative renderer for \l{Qt Quick} 2 that uses engine to render the contents of the scene graph. For more details, see \l{qtquick-visualcanvas-adaptations-software.html}{Software Adaptation}. -\section1 Direct3D 12 (experimental) - -The Direct3D 12 adaptation is an alternative renderer for \l{Qt Quick} 2 when running on Windows -10, both for Win32 and UWP applications. For more details, see -\l{qtquick-visualcanvas-adaptations-d3d12.html}{Direct3D 12 Adaptation}. - \section1 OpenVG The OpenVG adaptation is an alternative renderer for \l{Qt Quick} 2 that renders the contents of @@ -101,10 +98,11 @@ graphics. For more details, see \page qtquick-visualcanvas-adaptations-software.html The Software adaptation is an alternative renderer for \l {Qt Quick} 2 that uses the Raster paint -engine to render the contents of the scene graph, instead of OpenGL. Consequently, some features -and optimizations are not available. Most Qt Quick 2 applications can run without any modification, -but any attempts to use unsupported features are ignored. By using the Software adaptation, it is -possible to run Qt Quick 2 applications on hardware and platforms that do not have OpenGL support. +engine to render the contents of the scene graph, instead of a hardware-accelerated 3D graphics API. +Consequently, some features and optimizations are not available. Most Qt Quick 2 applications can run +without any modification, but any attempts to use unsupported features are ignored. +By using the Software adaptation, it is possible to run Qt Quick 2 applications on hardware and +platforms that do not have \l{topics-graphics}{hardware-accelerated 3D graphics API} support. The Software adaptation was previously known as the Qt Quick 2D Renderer. However, unlike the 2D Renderer, this new, integrated version supports partial updates. This means that a full update @@ -115,12 +113,6 @@ updates can significantly improve performance for many applications. ShaderEffect components in QtQuick 2 cannot be rendered by the Software adaptation. -\section2 Qt Graphical Effects Module - -\l {Qt Graphical Effects} uses ShaderEffect items to render effects. If you use graphical effects -from this module, then you should not hide the source item so that the original item can still be -rendered. - \section2 Particle Effects It is not possible to render particle effects with the Software adaptation. Whenever possible, @@ -130,247 +122,13 @@ even though they are not visible. \section2 Rendering Text The text rendering with the Software adaptation is based on software rasterization and does not -respond as well to transformations such as scaling, compared to when using OpenGL. The quality is -similar to choosing \l [QML] {Text::renderType}{Text.NativeRendering} with \l [QML] {Text} items. - -\section2 Qt Multimedia VideoOutput - -The Qt Multimedia module's VideoOutput item is not supported with the Software adaptation. This -is because VideoOutput uses the QVideoRendererControl item which requires custom QSGGeometryNode -behavior, which is only present in the default OpenGL adaptation. +respond as well to transformations such as scaling, compared to when using a hardware-accelerated +3D graphics API. The quality is similar to choosing \l [QML] {Text::renderType}{Text.NativeRendering} +with \l [QML] {Text} items. */ /*! -\title Qt Quick Direct3D 12 Adaptation -\page qtquick-visualcanvas-adaptations-d3d12.html - -The Direct3D 12 adaptation for Windows 10, both in Win32 (\c windows platform plugin) and in UWP -(\c winrt platform plugin), is shipped as a dynamically loaded plugin. This adaptation doesn't work -on earlier Windows versions. Building this plugin is enabled automatically, whenever the necessary -D3D and DXGI develpoment files are present. In practice, this currently means Visual Studio 2015 -and newer. - -The adaptation is available both in normal, OpenGL-enabled Qt builds, and also when Qt is -configured with \c{-no-opengl}. However, it's never the default, meaning that the user or the -application has to explicitly request it by setting the \c{QT_QUICK_BACKEND} environment variable -to \c{d3d12} or by calling QQuickWindow::setSceneGraphBackend(). - -\section2 Motivation - -This experimental adaptation is the first Qt Quick backend that focuses on a modern, lower-level -graphics API in combination with a windowing system interface that's different from the traditional -approaches used in combination with OpenGL. - -This adaptation also allows better integration with Windows, as Direct3D is the primary -vendor-supported solution. Consequently, there are fewer problems anticipated with drivers, -operations like window resizes, and special events like graphics device loss caused by device -resets or graphics driver updates. - -Performance-wise, the general expectation is a somewhat lower CPU usage compared to OpenGL, due to -lower driver overhead, and a higher GPU utilization with less idle time wastage. The backend -doesn't heavily utilize threads yet, which means there are opportunities for further improvements -in the future, for example to further optimize image loading. - -The D3D12 backend also introduces support for pre-compiled shaders. All the backend's own shaders -(used by the built-in materials on which the Rectangle, Image, Text, and other QML types are built -with) are compiled to D3D shader bytecode when you compile Qt. Applications using ShaderEffect -items can choose to ship bytecode either in regular files, via the Qt resource system, or use -High Level Shading Language for DirectX (HLSL) source strings. Unlike OpenGL, the compilation for -HLSL is properly threaded, meaning shader compilation won't block the application and its user -interface. - -\section2 Graphics Adapters - -The plugin does not necessarily require hardware acceleration. You can also use WARP, the Direct3D -software rasterizer. By default, the first adapter providing hardware acceleration is chosen. To -override this and use another graphics adapter or to force the use of the software rasterizer, set -the \c{QT_D3D_ADAPTER_INDEX} environment variable to the index of the adapter. The adapters -discovered are printed at startup when \c{QSG_INFO} or the \c{qt.scenegraph.general} logging -category is enabled. - -\section2 Troubleshooting - -If you encounter issues, always set the \c{QSG_INFO} and \c{QT_D3D_DEBUG} environment variables -to \c 1, to get debug and warning messages printed on the debug output. \c{QT_D3D_DEBUG} enables -the Direct3D debug layer. - -\note The debug layer shouldn't be enabled in production use, since it can significantly impact -performance (CPU load) due to increased API overhead. - -\section2 Render Loops - -By default, the D3D12 adaptation uses a single-threaded render loop similar to OpenGL's \c windows -render loop. A threaded variant is also available, that you can request by setting the -\c{QSG_RENDER_LOOP} environment variable to \c threaded. However, due to conceptual limitations in -DXGI, the windowing system interface, the threaded loop is prone to deadlocks when multiple -QQuickWindow or QQuickView instances are shown. Consequently, for the time being, the default is -the single-threaded loop. This means that with the D3D12 backend, applications are expected to move -their work from the main (GUI) thread out to worker threads, instead of expecting Qt to keep the -GUI thread responsive and suitable for heavy, blocking operations. - -For more information see \l{qtquick-visualcanvas-scenegraph.html}{Qt Quick Scene Graph} for -details on render loops and -\l{https://docs.microsoft.com/en-us/windows/desktop/direct3darticles/dxgi-best-practices#multithreading-and-dxgi}{Multithreading and DXGI} -regarding the issues with multithreading. - -\section2 Renderer - -The scene graph renderer in the D3D12 adaptation currently doesn't perform any batching. This is -less of an issue, unlike OpenGL, because state changes don't present any problems in the first -place. The simpler renderer logic can also lead to lower CPU overhead in some cases. The trade-offs -between the various approaches are currently under research. - -\section2 Shader Effects - -The ShaderEffect QML type is fully functional with the D3D12 adaptation as well. However, the -interpretation of the fragmentShader and vertexShader properties is different than with OpenGL. - -With D3D12, these strings can either be a URL for a local file, a file in the resource system, -or an HLSL source string. Using a URL for a local file or a file in the resource system -indicates that the file in question contains pre-compiled D3D shader bytecode generated by the -\c fxc tool, or, alternatively, HLSL source code. The type of file is detected automatically. -This means that the D3D12 backend supports all options from GraphicsInfo.shaderCompilationType -and GraphicsInfo.shaderSourceType. - -Unlike OpenGL, whenever you open a file, there is a QFileSelector with the extra \c hlsl selector -used. This provides easy creation of ShaderEffect items that are functional across both backends, -for example by placing the GLSL source code into \c{shaders/effect.frag}, the HLSL source code or -- preferably - pre-compiled bytecode into \c{shaders/+hlsl/effect.frag}, while simply writing -\c{fragmentShader: "qrc:shaders/effect.frag"} in QML. For more details, see ShaderEffect. - -\section2 Multisample Render Targets - -The Direct3D 12 adaptation ignores the QSurfaceFormat set on the QQuickWindow or QQuickView, or -set via QSurfaceFormat::setDefaultFormat(), with two exceptions: QSurfaceFormat::samples() and -QSurfaceFormat::alphaBufferSize() are still taken into account. When the sample value is greater -than 1, multisample offscreen render targets will be created with the specified sample count at -the maximum supported quality level. The backend automatically performs resolving into the -non-multisample swapchain buffers after each frame. - -\section2 Semi-transparent Windows - -When the alpha channel is enabled either via QQuickWindow::setDefaultAlphaBuffer() or by setting -alphaBufferSize to a non-zero value in the window's QSurfaceFormat or in the global format managed -by QSurfaceFormat::setDefaultFormat(), the D3D12 backend will create a swapchain for composition -and go through DirectComposition. This is necessary, because the mandatory flip model swapchain -wouldn't support transparency otherwise. - -Therefore, it's important not to unneccessarily request an alpha channel. When the alphaBufferSize -is 0 or the default -1, all these extra steps can be avoided and the traditional window-based -swapchain is sufficient. - -On WinRT, this isn't relevant because the backend there always uses a composition swapchain which -is associated with the ISwapChainPanel that backs QWindow on that platform. - -\section2 Mipmaps - -Mipmap generation is supported and handled transparently to the applications via a built-in compute -shader. However, at the moment, this feature is experimental and only supports power-of-two images. -Textures of other size will work too, but this involves a QImage-based scaling on the CPU first. -Therefore, avoid enabling mipmapping for Non-Power-Of-Two (NPOT) images whenever possible. - -\section2 Image Formats - -When creating textures via C++ scene graph APIs like QQuickWindow::createTextureFromImage(), 32-bit -formats won't involve any conversion, they'll map directly to the corresponding \c{R8G8B8A8_UNORM} -or \c{B8G8R8A8_UNORM} format. Everything else will trigger a QImage-based format conversion on the -CPU first. - -\section2 Unsupported Features - -Particles and some other OpenGL-dependent utilities, like QQuickFramebufferObject, are currently -not supported. - -Like with \l{qtquick-visualcanvas-adaptations-software.html}{Software adaptation}, text is always -rendered using the native method. Distance field-based text rendering is currently not implemented. - -The shader sources in the \l {Qt Graphical Effects} module have not been ported to any format other -than the OpenGL 2.0 compatible one, meaning that the QML types provided by that module are currently -not functional with the D3D12 backend. - -Texture atlases are currently not in use. - -The renderer may lack support for certain minor features, such as drawing points and lines with a -width other than 1. - -Custom Qt Quick items using custom scene graph nodes can be problematic because materials are -inherently tied to the graphics API. Therefore, only items that use the utility rectangle and image -nodes are functional across all adaptations. - -QQuickWidget and its underlying OpenGL-based compositing architecture is not supported. If you need -to mix with QWidget-based user interfaces, use QWidget::createWindowContainer() to embed the native -window of the QQuickWindow or QQuickView. - -Finally, rendering via QSGEngine and QSGAbstractRenderer is not feasible with the D3D12 adaptation -at the moment. - -\section2 Related APIs - -To integrate custom Direct3D 12 rendering, use QSGRenderNode in combination with -QSGRendererInterface. This approach doesn't rely on OpenGL contexts or API specifics like -framebuffers, and allows exposing the graphics device and command buffer from the adaptation. It's -not necessarily suitable for easy integration of all types of content, in particular true 3D, so -it'll likely get complemented by an alternative to QQuickFramebufferObject in future releases. - -To perform runtime decisions based on the adaptation, use QSGRendererInterface from C++ and -GraphicsInfo from QML. They can also be used to check the level of shader support: shading -language, compilation approach, and so on. - -When creating custom items, use the new QSGRectangleNode and QSGImageNode classes. These replace -the now deprecated QSGSimpleRectNode and QSGSimpleTextureNode. Unlike their predecessors, these new -classes are interfaces, and implementations are created via the QQuickWindow::createRectangleNode() -and QQuickWindow::createImageNode() factory functions. - -\section2 Advanced Configuration - -The D3D12 adaptation can keep multiple frames in flight, similar to modern game engines. This is -somewhat different from the traditional "render - swap - wait for vsync" model and allows for -better GPU utilization at the expense of higher resource use. This means that the renderer will -be a number of frames ahead of what is displayed on the screen. - -For a discussion of flip model swap chains and the typical configuration parameters, refer to -\l{https://software.intel.com/en-us/articles/sample-application-for-direct3d-12-flip-model-swap-chains} -{Sample Application for Direct3D 12 Flip Model Swap Chains}. - -Vertical synchronization is always enabled, meaning Present() is invoked with an interval of 1. - -The configuration can be changed by setting the following environment variables: - -\table - \header - \li Environment variable - \li Description - \row - \li \c{QT_D3D_BUFFER_COUNT} - \li The number of swap chain buffers in range 2 - 4. The default value is 3. - \row - \li \c{QT_D3D_FRAME_COUNT} - \li The number of frames prepared without blocking in range 1 - 4. The default value is 2. - Present() starts blocking after queuing 3 frames (regardless of - \c{QT_D3D_BUFFER_COUNT}), unless the waitable object is in use. Every additional frame - increases GPU resource usage since geometry and constant buffer data needs to be - duplicated, and involves more bookkeeping on the CPU side. - \row - \li \c{QT_D3D_WAITABLE_SWAP_CHAIN_MAX_LATENCY} - \li The frame latency in range 1 - 16. The default value is 0 (disabled). - Changes the limit for Present() and triggers a wait for an available swap chain buffer - when beginning each frame. For a detailed discussion, see the article linked above. - \note Currently, this behavior is experimental. - \row - \li \c{QT_D3D_BLOCKING_PRESENT} - \li The time the CPU should wait, a non-zero value, for the GPU to finish its work after - each call to Present(). The default value is 0 (disabled). This behavior effectively - kills all parallelism but makes the behavior resemble the traditional - swap-blocks-for-vsync model, which can be useful in some special cases. However, this - behavior is not the same as setting the frame count to 1 because that still avoids - blocking after Present(), and may only block when starting to prepare the next frame - (or may not block at all depending on the time gap between the frames). -\endtable - -*/ - -/*! \title Qt Quick OpenVG Adaptation \page qtquick-visualcanvas-adaptations-openvg.html @@ -417,12 +175,6 @@ to take advantage of Image Filter operations in the OpenVG API to get effects th what ShaderEffects provides in custom items. To integrate custom OpenVG rendering, use QSGRenderNode in combination with QSGRendererInterface. -\section2 Qt Graphical Effects Module - -\l {Qt Graphical Effects} uses ShaderEffect items to render effects. If you use graphical effects -from this module, then you shouldn't hide the source item so that the original item can still be -rendered. - \section2 Particle Effects It's not possible to render particle effects with the OpenVG adaptation. Whenever possible, remove |