Fix AMW.color difference between single and multi-process mode

Change-Id: I75242f768d5766d489ce11c1f0477dc095c51fe8
Pick-to: 6.7
Reviewed-by: Dominik Holland <dominik.holland@qt.io>

3 files changed, 12 insertions, 3 deletions

diff --git a/src/application-main-lib/waylandapplicationmanagerwindowimpl.cpp b/src/application-main-lib/waylandapplicationmanagerwindowimpl.cpp
index 8881b452..fb4c88d9 100644
--- a/src/application-main-lib/waylandapplicationmanagerwindowimpl.cpp
+++ b/src/application-main-lib/waylandapplicationmanagerwindowimpl.cpp
@@ -40,6 +40,8 @@ WaylandApplicationManagerWindowImpl::WaylandApplicationManagerWindowImpl(Applica
     , m_applicationMain(applicationMain)
     , m_qwindow(new AMQuickWindowQmlImpl(window))
 {
+    m_color = qUnpremultiply(m_qwindow->color().rgba64());
+
     QObject::connect(m_qwindow, &AMQuickWindowQmlImpl::windowTitleChanged,
                      window, &ApplicationManagerWindow::titleChanged);
     QObject::connect(m_qwindow, &AMQuickWindowQmlImpl::xChanged,
@@ -347,13 +349,15 @@ void WaylandApplicationManagerWindowImpl::setOpacity(qreal opactity)
 
 QColor WaylandApplicationManagerWindowImpl::color() const
 {
-    return m_qwindow ? m_qwindow->color() : QColor { };
+    return m_qwindow ? m_color : QColor { };
 }
 
 void WaylandApplicationManagerWindowImpl::setColor(const QColor &c)
 {
-    if (m_qwindow)
-        m_qwindow->setColor(c);
+    if (m_qwindow) {
+        m_color = c; // qUnpremultiply(qPremultiply(...)) introduces rounding errors
+        m_qwindow->setColor(qPremultiply(c.rgba64()));
+    }
 }
 
 bool WaylandApplicationManagerWindowImpl::isActive() const
diff --git a/src/application-main-lib/waylandapplicationmanagerwindowimpl.h b/src/application-main-lib/waylandapplicationmanagerwindowimpl.h
index b0eb3d19..eaf638b9 100644
--- a/src/application-main-lib/waylandapplicationmanagerwindowimpl.h
+++ b/src/application-main-lib/waylandapplicationmanagerwindowimpl.h
@@ -74,6 +74,7 @@ public:
 private:
     QPointer<ApplicationMain> m_applicationMain;
     QPointer<AMQuickWindowQmlImpl> m_qwindow;
+    QColor m_color;
 };
 
 
diff --git a/src/shared-main-lib/applicationmanagerwindow.cpp b/src/shared-main-lib/applicationmanagerwindow.cpp
index 9398f7fe..1d37abeb 100644
--- a/src/shared-main-lib/applicationmanagerwindow.cpp
+++ b/src/shared-main-lib/applicationmanagerwindow.cpp
@@ -532,6 +532,10 @@ void ApplicationManagerWindow::setOpacity(qreal opacity)
     The background color for the window.
 
     Setting this property is more efficient than using a separate Rectangle.
+
+    \note Since version 6.7, if an alpha channel is used, it needs to be straight alpha. Pre 6.7
+          it needed to be pre-multiplied alpha (which is what the \l{Window} QML type still expects)
+          in multi-process and straight alpha in single-process mode.
 */
 QColor ApplicationManagerWindow::color() const
 {