Support windows with sRGB-capable default framebuffers in QSurfaceFormat

Backend implementation is done for GLX for now. WGL and EGL may follow
later on.

[ChangeLog][QtGui] Added support for requesting OpenGL windows with
sRGB-capable default framebuffers. While this is implicit on some
platforms, QSurfaceFormat now has the necessary flags to request
such windows in a cross-platform manner.

Task-number: QTBUG-50987
Change-Id: I4df1f786e41e63396f46920a81afdf5ecb5eedea
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 68 insertions, 1 deletions

diff --git a/src/gui/kernel/qsurfaceformat.cpp b/src/gui/kernel/qsurfaceformat.cpp
index 000d727380..574310f554 100644
--- a/src/gui/kernel/qsurfaceformat.cpp
+++ b/src/gui/kernel/qsurfaceformat.cpp
@@ -73,6 +73,7 @@ public:
         , major(2)
         , minor(0)
         , swapInterval(1) // default to vsync
+        , colorSpace(QSurfaceFormat::DefaultColorSpace)
     {
     }
 
@@ -91,7 +92,8 @@ public:
           profile(other->profile),
           major(other->major),
           minor(other->minor),
-          swapInterval(other->swapInterval)
+          swapInterval(other->swapInterval),
+          colorSpace(other->colorSpace)
     {
     }
 
@@ -110,6 +112,7 @@ public:
     int major;
     int minor;
     int swapInterval;
+    QSurfaceFormat::ColorSpace colorSpace;
 };
 
 /*!
@@ -124,6 +127,12 @@ public:
     contains surface configuration parameters such as OpenGL profile and
     version for rendering, whether or not to enable stereo buffers, and swap
     behaviour.
+
+    \note When troubleshooting context or window format issues, it can be
+    helpful to enable the logging category \c{qt.qpa.gl}. Depending on the
+    platform, this may print useful debug information when it comes to OpenGL
+    initialization and the native visual or framebuffer configurations which
+    QSurfaceFormat gets mapped to.
 */
 
 /*!
@@ -199,6 +208,22 @@ public:
 */
 
 /*!
+    \enum QSurfaceFormat::ColorSpace
+
+    This enum is used to specify the preferred color space, controlling if the
+    window's associated default framebuffer is able to do updates and blending
+    in a given encoding instead of the standard linear operations.
+
+    \value DefaultColorSpace The default, unspecified color space.
+
+    \value sRGBColorSpace When \c{GL_ARB_framebuffer_sRGB} or
+    \c{GL_EXT_framebuffer_sRGB} is supported by the platform and this value is
+    set, the window will be created with an sRGB-capable default
+    framebuffer. Note that some platforms may return windows with a sRGB-capable
+    default framebuffer even when not requested explicitly.
+ */
+
+/*!
     Constructs a default initialized QSurfaceFormat.
 
     \note By default OpenGL 2.0 is requested since this provides the highest
@@ -736,6 +761,47 @@ int QSurfaceFormat::swapInterval() const
     return d->swapInterval;
 }
 
+/*!
+    Sets the preferred \a colorSpace.
+
+    For example, this allows requesting windows with default framebuffers that
+    are sRGB-capable on platforms that support it.
+
+    \note When the requested color space is not supported by the platform, the
+    request is ignored. Query the QSurfaceFormat after window creation to verify
+    if the color space request could be honored or not.
+
+    \note This setting controls if the default framebuffer of the window is
+    capable of updates and blending in a given color space. It does not change
+    applications' output by itself. The applications' rendering code will still
+    have to opt in via the appropriate OpenGL calls to enable updates and
+    blending to be performed in the given color space instead of using the
+    standard linear operations.
+
+    \since 5.10
+
+    \sa colorSpace()
+ */
+void QSurfaceFormat::setColorSpace(ColorSpace colorSpace)
+{
+    if (d->colorSpace != colorSpace) {
+        detach();
+        d->colorSpace = colorSpace;
+    }
+}
+
+/*!
+    \return the color space.
+
+    \since 5.10
+
+    \sa setColorSpace()
+*/
+QSurfaceFormat::ColorSpace QSurfaceFormat::colorSpace() const
+{
+    return d->colorSpace;
+}
+
 Q_GLOBAL_STATIC(QSurfaceFormat, qt_default_surface_format)
 
 /*!
@@ -841,6 +907,7 @@ QDebug operator<<(QDebug dbg, const QSurfaceFormat &f)
                   << ", samples " << d->numSamples
                   << ", swapBehavior " << d->swapBehavior
                   << ", swapInterval " << d->swapInterval
+                  << ", colorSpace " << d->colorSpace
                   << ", profile  " << d->profile
                   << ')';