- Qt 5.15
- Qt for Windows - Requirements
- Qt 5.15.16 Reference Documentation

# Qt for Windows - Requirements

This page describes the required libraries and environment for Qt for Windows.

## Libraries

The following third-party libraries may be used when running Qt 5 applications on Windows.

- OpenSSL Toolkit: Qt can make use of OpenSSL to support Secure Socket Layer (SSL) communication.
- ICU: Qt 5 can make use of the ICU library for enhanced UNICODE and Globalization support (see QTextCodec, QCollator::setNumericMode()).

  At compile time, the include and lib folders of the ICU installation must be appended to the `INCLUDE` and `LIB` environment variables. At run-time, the ICU DLLs need to be found by copying the DLLs to the application folder or by adding the bin folder of the ICU installation to the `PATH` environment variable.

- ANGLE: This library converts OpenGL ES 2.0 API calls to DirectX 11 or DirectX 9 calls (depending on availability), removing the need to install graphics drivers on the target machines.

### SSL

Support for Secure Sockets Layer (SSL) communication is provided by the OpenSSL Toolkit, which must be obtained separately. Download the latest version of the toolkit that is supported by Qt.

Qt can be configured to use OpenSSL in three ways:

- Qt Network loads OpenSSL libraries (DDLs) when first needed, at runtime. If not found, the application continues to run, but fails to handle SSL communication.

  All official Qt binary builds use this configuration.

  The OpenSSL libraries are looked up first in the directory of the executable, then in the Windows System directory (usually `C:\Windows\system32`), and finally in all directories listed in the `PATH` environment variable.

- Qt Network links against the OpenSSL libraries. If they cannot be found at load time, the application fails to start.
- Qt Network compiles against a static version of the OpenSSL libs, and OpenSSL becomes part of the Qt5Network library.

If you compile Qt yourself, you can configure how Qt uses OpenSSL by setting either the `-openssl` / `-openssl-runtime` or `-openssl-linked` configure flags.

If OpenSSL is not found in the normal compiler include and library directories, you can set either the `OPENSSL_PREFIX`, or `OPENSSL_INCDIR` and `OPENSSL_LIBDIR` configure arguments. If `OPENSSL_PREFIX` is set, `OPENSSL_INCDIR` defaults to `OPENSSL_PREFIX/include` and `OPENSSL_LIBDIR` to `OPENSSL_PREFIX/lib`.

The actual libraries to link to can be tweaked by setting the `OPENSSL_LIBS`, `OPENSSL_LIBS_DEBUG`, and `OPENSSL_LIBS_RELEASE` configure arguments.

- To load OpenSSL at runtime, set the `-openssl-runtime` configure argument. Qt will try to find `openssl/ssl.h` and `openssl/opensslv.h` in the default include path of the compiler. You can specify an additional include directory by setting `OPENSSL_INCDIR`.

  For example:

       configure -openssl-runtime OPENSSL_INCDIR="C:\Program Files\OpenSSL-Win64\include"

- To link Qt Network against OpenSSL libraries, set the `-openssl-linked` configure argument. Use the `OPENSSL_PREFIX` variable to let Qt correctly locate and build against your OpenSSL installation:

  For example:

       configure -openssl-linked OPENSSL_PREFIX="C:\Program Files\OpenSSL-Win64"

- To link Qt Network against a static version of the OpenSSL libs, set the `-openssl-linked` argument, and set `OPENSSL_PREFIX`, or `OPENSSL_INCDIR` and `OPENSSL_LIBDIR`. In addition, you probably need to set the `OPENSSL_LIBS`, `OPENSSL_LIBS_DEBUG`, `OPENSSL_LIBS_RELEASE` configure arguments to let Qt correctly link against your static build of the OpenSSL libraries.

  For example:

       set OPENSSL_DIR=C:\Program Files\OpenSSL-Win64
       configure -openssl-linked OPENSSL_INCDIR="%OPENSSL_DIR%\include" OPENSSL_LIBDIR="%OPENSSL_DIR%\lib\VC\static" OPENSSL_LIBS="-lWs2_32 -lGdi32 -lAdvapi32 -lCrypt32 -lUser32" OPENSSL_LIBS_DEBUG="-llibssl64MDd -llibcrypto64MDd" OPENSSL_LIBS_RELEASE="-llibssl64MD -llibcrypto64MD"

See Secure Sockets Layer (SSL) Classes for further instructions on Qt with SSL support.

### ICU

From Qt 5.3 and onwards, configure does not link Qt Core against ICU libraries anymore by default. This reduces the size of a self-contained application package considerably.

Letting Qt Core utilize the ICU libraries however has following advantages:

- Behavior matches other platforms more closely.
- Extended set of text codecs (see QTextCodec).
- QLocale::toUpper(), QLocale::toLower() always use case conversion rules specific to the locale.
- QCollator::setNumericMode() does work consistently on all Windows versions.

To explicitly enable the use of ICU in Qt Core, pass `-icu` to `configure`:

     configure -icu

## Graphics Drivers

For Qt Quick 2 to work, a graphics driver that provides OpenGL 2.1 or higher is required. The default driver from Windows is OpenGL 1.1. Qt includes a version of the ANGLE project which is included from the Windows Qt installers. ANGLE implements the OpenGL ES 2.0 API on top of DirectX 11 or DirectX 9.

ANGLE requires that the DirectX SDK is installed when building Qt. If MSVC is used, the DirectX SDK will be provided by the Windows SDK. In this case, you will need at least Windows SDK 10. For MinGW builds, you have to install the DirectX SDK provided by Microsoft.

ANGLE chooses the render backend depending on availability. DirectX 11 is usually preferable. However, some graphics cards may not fully support it. For these cases, the environment variable `QT_ANGLE_PLATFORM` (introduced in Qt 5.4) can be used to control the render backend. Possible values are `d3d11`, `d3d9` and `warp`.

To use a custom version of ANGLE, set the `ANGLE_DIR` environment variable to point to the ANGLE source tree before building Qt.

If you installed additional OpenGL drivers from your hardware vendor, then you may want to consider using this version of OpenGL instead of ANGLE. To use OpenGL, pass the command line options `-opengl desktop` to the configure script.

     configure -opengl desktop

To use an OpenGL ES 2.0 emulator instead of ANGLE, use the configure options: `-opengl es2 -no-angle`.

     configure -opengl es2 -no-angle

### Dynamically Loading Graphics Drivers

In addition to the build time configuration, Qt supports choosing and loading the OpenGL implementation at runtime. To use this mode, pass `-opengl dynamic` to the configure script.

     configure -opengl dynamic

Note: As of Qt 5.5 this is the configuration used by the official, pre-built binary packages of Qt. It is strongly recommended to use it also in custom builds, especially for Qt binaries that are deployed alongside applications.

Note: Combining `-opengl dynamic` with `-static` is also possible, but be aware that ANGLE will not be statically linked into the applications in this case, it will still be built as a shared library.

This configuration is the most flexible because no dependencies or assumptions are hardcoded about the OpenGL implementation during build time. It allows robust application deployment. When a given environment fails to provide a proper OpenGL 2.0 implementation, it will fall back automatically to ANGLE. This fallback will be completely transparent to the application, and will allow Qt Quick or other OpenGL code to function by translating to Direct3D. Such a fallback could, for example, take place on a Windows 7 PC with no additional graphics drivers installed. On other machines, where there is sufficient OpenGL support, the normal desktop OpenGL drivers will be used. Additionally, pure software-based OpenGL implementations may be available as additional fallbacks in the future, allowing running Qt Quick applications without a GPU.

When configured with `-opengl dynamic`, neither Qt nor the applications built using `qmake` will link to the opengl32 (standard desktop OpenGL) or QtANGLE libraries. Instead, the appropriate library is chosen at runtime. By default, Qt will determine whether the system's opengl32.dll provides OpenGL 2 functions. If these are present, opengl32.dll is used, otherwise the ANGLE libraries (libEGL.dll and libGLESv2.dll) will be used. In case the ANGLE libraries are missing or initialization fails for some reason, an additional fallback is attempted by trying to load `opengl32sw.dll`. See below for details.

The loading mechanism can be configured through the `QT_OPENGL` environment variable and the following application attributes:

- `Qt::AA_UseDesktopOpenGL` Equivalent to setting `QT_OPENGL` to `desktop`.
- `Qt::AA_UseOpenGLES` Equivalent to setting `QT_OPENGL` to `angle`.
- `Qt::AA_UseSoftwareOpenGL` Equivalent to setting `QT_OPENGL` to `software`.

When a certain configuration is requested explicitly, no checks are done at application startup, that is, the system-provided opengl32.dll will not be examined.

The dynamic loading has a significant impact on applications that contain native OpenGL calls: they may fail to link since `qmake` no longer automatically adds opengl32.lib or libGLESv2.lib. Instead, applications are expected to use the OpenGL functions via the QOpenGLFunctions class. Thus the direct dependency on the OpenGL library is removed and all calls will be routed during runtime to the implementation chosen by Qt.

Applications that require a certain OpenGL implementation (for example, desktop OpenGL due to relying on features provided by OpenGL 3.0 or higher) should set the application attributes `Qt::AA_UseOpenGLES` or `Qt::AA_UseDesktopOpenGL` before instantiating QGuiApplication or QApplication. When these attributes are set, no other OpenGL implementations are considered. Additionally, if they wish to, such applications are free to make direct OpenGL function calls by adding opengl32.lib to their .pro project files: LIBS += opengl32.lib (Visual Studio) or LIBS += -lopengl32 (MinGW). The result is, from the application's perspective, equivalent to the `-opengl desktop` build configuration of Qt.

`Qt::AA_UseSoftwareOpenGL` is special in the sense that it will try to load an OpenGL implementation with a non-standard name. The default name is `opengl32sw.dll`. This allows shipping a software-only OpenGL implementation, for example a build of Mesa with llvmpipe, under this name. If necessary, the filename can be overridden by setting the `QT_OPENGL_DLL` environment variable.

It is possible to provide a JSON-format configuration file specifying which OpenGL implementation to use depending on the graphics card and driver version. The location is given by the environment variable `QT_OPENGL_BUGLIST`. Relative paths are resolved using `QLibraryInfo::SettingsPath` or `QStandardPaths::ConfigLocation`. The file utilizes the format of the driver bug list used in The Chromium Projects. It consists of a list of entries each of which specifies a set of conditions and a list of feature keywords. Typically, device id and vendor id are used to match a specific graphics card. They can be found in the output of the `qtdiag` or `dxdiag` tool.

The following feature keywords are relevant for choosing the OpenGL implementation:

- `disable_desktopgl` - Disables OpenGL. This ensures that Qt does not attempt to use regular OpenGL (opengl32.dll), and that it starts with ANGLE right away. This is useful to prevent bad OpenGL drivers from crashing the application.
- `disable_angle` - Disables ANGLE. Ensures that Qt does not attempt to use ANGLE (and so Direct3D).
- `disable_d3d11` - Disables the D3D11 rasterizer in ANGLE. Instead, the next D3D rendering option is tried first. The default order is: D3D11, D3D9, WARP, reference implementation.
- `disable_d3d9` - Disables the D3D9 rasterizer in ANGLE
- `disable_rotation` - Forces the application to run in landscape orientation always. It applies to OpengGL only and has no effect when using ANGLE or Software OpenGL implementations. This is intended for drivers that have issues with rotation. This feature keyword was introduced in Qt 5.6.
- `disable_program_cache` - Disable storing shader program binaries on disk. This feature keyword was introduced in Qt 5.12.

A sample file looks like:

     {
     "entries": [
     {
       "id": 1,
       "description": "Disable D3D11 on older nVidia drivers",
       "os": {
         "type": "win"
       },
       "vendor_id": "0x10de",
       "device_id": ["0x0DE9"],
       "driver_version": {
         "op": "<=",
         "value": "8.17.12.6973"
       },
       "features": [
         "disable_d3d11"
       ]
     },
     ...

When `QT_OPENGL_BUGLIST` is not specified, a built-in list will be used. This typically includes some older, less-capable graphics cards with `disable_desktopgl` set, in order to prevent Qt from using their unstable desktop OpenGL implementations and instead fall back to ANGLE right away.

In practice the most common combinations are expected to be the following:

- `disable_desktopgl` - In case the system provides OpenGL 2.0 or newer, but the driver is known to be unstable and prone to crash.
- `disable_desktopgl`, disable_angle - When no accelerated path is desired. This ensures that the only option Qt tries is the sofware rasterizer (opengl32sw.dll). Can be useful in virtual machines and applications that are deployed on a wide range of old systems.
- `disable_d3d11`, disable_d3d9 - When the accelerated D3D options are known to be unstable and WARP is desired (when available). Can be useful in virtual machines.

The supported keys for matching a given card or driver are the following. Note that some of these are specific to Qt.

- `os.type` - Operating system: `win`, `linux`, `macosx`, `android`
- `os.version` - Kernel version
- `os.release` - Specifies a list of operating system releases on Windows: `xp`, `vista`, `7`, `8`, `8.1`, `10`.
- `vendor_id` - Vendor from the adapter identifier
- `device_id` - List of PCI device IDs.
- `driver_version` - Driver version from the adapter identifier
- `driver_description` - Matches when the value is a substring of the driver description from the adapter identifier
- `gl_vendor` - Matches when the value is a substring of the `GL_VENDOR` string

To disable all blacklisting, set the environment variable `QT_NO_OPENGL_BUGLIST` to any value. This will skip reading any configuration files, and instead will assume that nothing is disabled, regardless of the driver or OS.

Note: While not typically needed, `QT_NO_OPENGL_BUGLIST` can become relevant in certain virtualized environments, with multiple, possibly virtual, graphics adapters present. If the logs from categories like qt.qpa.gl indicate that the detection of the driver and display adapter leads to incorrectly disabling OpenGL, it is then recommended to set this environment variable in order to enable the application to run normally. This environment variable was introduced in Qt 5.15.

## Building from Source

These tools are not needed to run Qt 5 applications, but they are required for building Qt 5 from source.

- Perl - Install a recent version of perl (for instance (Strawberry Perl) and add the installation location to your `PATH`.
- Python - Install Python from the here and add the installation location to your `PATH`.

ANGLE depends on these extra tools from the GnuWin32 and Win flex-bison projects, which are provided for your convenience in the gnuwin32/bin folder:

- GPerf
- Bison, Flex

The gnuwin32/bin folder should be added to the `PATH` variable.

Note: If you are building qtbase outside of qt5.git, you will need to download win_bison and win_flex from the link above and rename them to bison and flex.

For instructions for building the Qt 5 source, read the Qt for Windows - Building from Source page.

## Compilers

### Visual Studio

Qt can be built with Visual Studio 2015 (Update 2), Visual Studio 2017, Visual Studio 2019 and Build Tools for Visual Studio 2017 and 2019 (see also Supported Platforms).

### Intel C++ Compiler (Windows, Altix)

Qt has been tested successfully with:

- Windows - Intel(R) C++ Compiler for 32-bit applications, Version 9.1.040.
- Altix - Intel(R) C++ Itanium(R) Compiler for Itanium(R)-based applications Version 8.1 Build 20050406 Package ID: l_cc_pc_8.1.030

### GCC (MinGW-builds)

The minimum version of MinGW-builds supported is GCC 5.1.0 (64bit, 32bit), available from its download page.

For more information about the MinGW builds, visit the Reference Configuration section of the supported platforms page.

### Clang(clang-cl)

Qt has been tested successfully with Clang 3.8(llvm svn rev. 256453 and clang svn rev. 256453). Visual Studio 2015 Update 1 was used to build clang. Mkspec is using the clang-cl tool to build Qt. Clang 3.8 does not support precompiled headers.

### Building Qt WebEngine

Qt WebEngine has additional build requirements which are listed in the Qt WebEngine Platform Notes.

## QDoc Dependencies

Since version 5.11, QDoc uses Clang to parse C++ code. If you wish to build QDoc manually, refer to Installing Clang for QDoc for specific build requirements.

See also QDoc Dependencies.