Add default format to QSurfaceFormat

Add defaultFormat() and setDefaultFormat() statics to QSurfaceFormat.
These define the default values for the requestedFormat members of
QOpenGLContext, QWindow and QOpenGLWidget (and implicitly QOpenGLWindow,
QQuickWindow, etc.)

This replaces QQuickWindow::setDefaultFormat() which can now be removed.

The main inspiration here is not the convenience (avoiding setFormat() calls
for all windows/widgets), but robustness: by setting the format once at the start
of the application, all windows and contexts, including the internal share context
used by QOpenGLWidget and QQuickWidget, will use the same format, eliminating
the possibility of failing due to trying to share between incompatible contexts.

Furthermore, since such a functionality is anyway mandatory for QQuickWindow
(due to the possibility of creating windows from QML code), extending it to
QSurfaceFormat and QOpenGLContext/QWindow is the next logical step.

Change-Id: Ie94486adc489d17fecfcebb7050fecedffd2688b
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/src/gui/kernel/qsurfaceformat.cpp b/src/gui/kernel/qsurfaceformat.cpp
index 2b8e611dff..f077abc6a2 100644
--- a/src/gui/kernel/qsurfaceformat.cpp
+++ b/src/gui/kernel/qsurfaceformat.cpp
@@ -196,6 +196,9 @@ public:
 
 /*!
     Constructs a default initialized QSurfaceFormat.
+
+    \note By default OpenGL 2.0 is requested since this provides the highest
+    grade of portability between platforms and OpenGL implementations.
 */
 QSurfaceFormat::QSurfaceFormat() : d(new QSurfaceFormatPrivate)
 {
@@ -730,6 +733,43 @@ int QSurfaceFormat::swapInterval() const
     return d->swapInterval;
 }
 
+Q_GLOBAL_STATIC(QSurfaceFormat, qt_default_surface_format)
+
+/*!
+    Sets the global default surface \a format.
+
+    This format is used by default in QOpenGLContext, QWindow, QOpenGLWidget and
+    similar classes.
+
+    It can always be overridden on a per-instance basis by using the class in
+    question's own setFormat() function. However, it is often more convenient to
+    set the format for all windows once at the start of the application. It also
+    guarantees proper behavior in cases where shared contexts are required,
+    because settings the format via this function guarantees that all contexts
+    and surfaces, even the ones created internally by Qt, will use the same
+    format.
+
+    \since 5.4
+    \sa defaultFormat()
+ */
+void QSurfaceFormat::setDefaultFormat(const QSurfaceFormat &format)
+{
+    *qt_default_surface_format() = format;
+}
+
+/*!
+    Returns the global default surface format.
+
+    When setDefaultFormat() is not called, this is a default-constructed QSurfaceFormat.
+
+    \since 5.4
+    \sa setDefaultFormat()
+ */
+QSurfaceFormat QSurfaceFormat::defaultFormat()
+{
+    return *qt_default_surface_format();
+}
+
 /*!
     Returns \c true if all the options of the two QSurfaceFormat objects
     \a a and \a b are equal.