QWGLNativeContext Class

A class encapsulating a WGL context on Windows with desktop OpenGL (opengl32.dll) More...

Header: #include <QWGLNativeContext>
Since: Qt 5.4

Public Functions

QWGLNativeContext(HGLRC ctx, HWND wnd)
HGLRC context() const
HWND window() const

Detailed Description

A class encapsulating a WGL context on Windows with desktop OpenGL (opengl32.dll)

Note: There is no binary compatibility guarantee for this class, meaning that an application using it is only guaranteed to work with the Qt version it was developed against.

QWGLNativeContext is a value class that can be passed to QOpenGLContext::setNativeHandle(). When creating a QOpenGLContext with the native handle set, no new context will get created. Instead, the provided handles are used, without taking ownership. This allows wrapping a context created by an external framework or rendering engine. The typical usage will be similar to the following snippet:

#include <QtPlatformSupport/QWGLNativeContext>
...create and retrieve the WGL context and the corresponding window...
QOpenGLContext *context = new QOpenGLContext;
QWGLNativeContext nativeContext(hglrc, hwnd);

The window is needed because the its pixel format will be queried. When the adoption is successful, QOpenGLContext::format() will return a QSurfaceFormat describing this pixel format.

It is recommended to restrict the usage of QOpenGLContexts created this way. Various platform-specific behavior and issues may prevent such contexts to be made current with windows (surfaces) created by Qt due to non-matching pixel formats for example. A potentially safer solution is to use the wrapped context only to set up sharing and perform Qt-based rendering offscreen, using a separate, dedicated QOpenGLContext. The resulting textures are then accessible in the foreign context too.

...like above...
QOpenGLContext *qtcontext = new QOpenGLContext;
...use qtcontext for rendering with Qt...

In addition to being used with QOpenGLContext::setNativeHandle(), this class is used also to retrieve the native context handle, that is, a HGLRC value, from a QOpenGLContext. Calling QOpenGLContext::nativeHandle() returns a QVariant which, on Windows with opengl32.dll at least, will contain a QWGLNativeContext:

QVariant nativeHandle = context->nativeHandle();
if (!nativeHandle.isNull() && nativeHandle.canConvert<QWGLNativeContext>()) {
    QWGLNativeContext nativeContext = nativeHandle.value<QWGLNativeContext>();
    HGLRC hglrc = nativeContext.context();

See also QOpenGLContext::setNativeHandle() and QOpenGLContext::nativeHandle().

Member Function Documentation


Construct a new instance with no handles.

QWGLNativeContext::QWGLNativeContext(HGLRC ctx, HWND wnd)

Constructs a new instance with the provided ctx context handle and wnd window handle.

Note: The window specified by wnd must have its pixel format set to a format compatible with the context's. If no SetPixelFormat() call was made on any device context belonging to the window, adopting the context will fail.

HGLRC QWGLNativeContext::context() const

Returns the WGL context.

HWND QWGLNativeContext::window() const

Note: The window handle is not available when the QWGLNativeContext is queried from a regular, non-adopted QOpenGLContext using QOpenGLContext::nativeHandle(). This is because the windows platform plugin creates WGL contexts using a dummy window that is not available afterwards. Instead, the native window handle (HWND) is queriable from a QWindow via QPlatformNativeInterface::nativeResourceForWindow() using the "handle" resource key. Note however that the window will not have its pixel format set until it is first associated with a context via QOpenGLContext::makeCurrent().

Returns handle for the window for which the context was created.

© 2016 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.