add color picking support on wayland using the XDG desktop portal

On wayland applications are not trusted to perform screen grabs by
default, it is however possible to let the user specifically pick the
color of a pixel using the XDG desktop portal (otherwise used for
sandboxing etc.). Try to use this portal on unix systems by default.

To support this use case some extra abstraction is necessary as this
constitutes a platformservice rather than a platform feature. To that
end the QPlatformService has gained a capability system and a pure
virtual helper class to facilitate asynchronous color picking. When
supported the color picking capability takes precedence over the custom
picking code in QColorDialog.

Fixes: QTBUG-81538
Change-Id: I4acb3af11d459e9d5ebefe5abbb41e50e3ccf7f0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/gui/kernel/qplatformservices.cpp b/src/gui/kernel/qplatformservices.cpp
index a0db26dda3..1c8062389d 100644
--- a/src/gui/kernel/qplatformservices.cpp
+++ b/src/gui/kernel/qplatformservices.cpp
@@ -19,6 +19,19 @@ QT_BEGIN_NAMESPACE
     \brief The QPlatformServices provides the backend for desktop-related functionality.
 */
 
+/*!
+    \enum QPlatformServices::Capability
+
+    Capabilities are used to determine a specific platform service's availability.
+
+    \value ColorPickingFromScreen The platform natively supports color picking from screen.
+    This capability indicates that the platform supports "opaque" color picking, where the
+    platform implements a complete user experience for color picking and outputs a color.
+    This is in contrast to the application implementing the color picking user experience
+    (taking care of showing a cross hair, instructing the platform integration to obtain
+    the color at a given pixel, etc.). The related service function is pickColor().
+ */
+
 QPlatformServices::QPlatformServices()
 { }
 
@@ -49,5 +62,16 @@ QByteArray QPlatformServices::desktopEnvironment() const
     return QByteArray("UNKNOWN");
 }
 
+QPlatformServiceColorPicker *QPlatformServices::colorPicker(QWindow *parent)
+{
+    Q_UNUSED(parent);
+    return nullptr;
+}
+
+bool QPlatformServices::hasCapability(Capability capability) const
+{
+    Q_UNUSED(capability)
+    return false;
+}
 
 QT_END_NAMESPACE