gnu: qtwayland@5: Fix rendering bug on lodpi screen in hidpi mode.

* gnu/packages/patches/qtwayland-5.15.18-0056-redraw-hidpi.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/qt.scm (qtwayland-5)[source]: Use it.

Change-Id: Iaa2c85b7f17728836465f1ae50f65a1b8dea60ef
Merges: #7127

3 files changed, 38 insertions, 1 deletions

diff --git a/gnu/local.mk b/gnu/local.mk
index 237b0ca6c6e..c7db93ecd68 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -2320,6 +2320,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/qtwayland-5.15.18-0053-client-remove-some-surface-commits.patch  \
   %D%/packages/patches/qtwayland-5.15.18-0054-client-avoid-locking-resizing-in-qwaylandshmbackings.patch        \
   %D%/packages/patches/qtwayland-5.15.18-0055-bradient-use-qwaylandwindow-actual-window-title.patch     \
+  %D%/packages/patches/qtwayland-5.15.18-0056-redraw-hidpi.patch        \
   %D%/packages/patches/qtwebsockets-6.9-fix-tst_QWebSocket.patch\
   %D%/packages/patches/rabbitmq-defaults.patch          \
   %D%/packages/patches/radare2-fix-meson-build-to-use-sys-qjs.patch     \
diff --git a/gnu/packages/patches/qtwayland-5.15.18-0056-redraw-hidpi.patch b/gnu/packages/patches/qtwayland-5.15.18-0056-redraw-hidpi.patch
new file mode 100644
index 00000000000..a18136a2e72
--- /dev/null
+++ b/gnu/packages/patches/qtwayland-5.15.18-0056-redraw-hidpi.patch
@@ -0,0 +1,35 @@
+From 30ed491e1ea190591260f1b73b9dad2a5926e113 Mon Sep 17 00:00:00 2001
+From: Danny Milosavljevic <dannym@friendly-machines.com>
+Date: Mon, 16 Feb 2026 00:00:00 +0100
+Subject: [PATCH] Client: Force full repaint after output scale change
+See: <https://invent.kde.org/qt/qt/qtwayland/-/merge_requests/89>
+
+In handleScreensChanged(), after ensureSize(), call
+requestUpdate() and sendExposeEvent() for the entire window.
+This forces a full repaint at the new scale.
+---
+ src/client/qwaylandwindow.cpp | 8 ++++++++
+ 1 file changed, 8 insertions(+)
+
+diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
+index 7c338d27a..a8d5fe2e4 100644
+--- a/src/client/qwaylandwindow.cpp
++++ b/src/client/qwaylandwindow.cpp
+@@ -1075,6 +1075,14 @@ void QWaylandWindow::handleScreensChanged()
+         if (mSurface && mDisplay->compositorVersion() >= 3)
+             mSurface->set_buffer_scale(mScale);
+         ensureSize();
++        // The buffer was recreated at the new scale but no widgets
++        // are marked dirty, so it is uninitialized (black).  Force a
++        // full repaint by requesting an update and sending an expose
++        // event for the entire window.
++        if (isExposed()) {
++            window()->requestUpdate();
++            sendExposeEvent(QRect(QPoint(), geometry().size()));
++        }
+     }
+ }
+ 
+-- 
+GitLab
+
diff --git a/gnu/packages/qt.scm b/gnu/packages/qt.scm
index 8f0e5d570aa..03eaa2db29e 100644
--- a/gnu/packages/qt.scm
+++ b/gnu/packages/qt.scm
@@ -2290,7 +2290,8 @@ record media, and manage a collection of media content.")
                         "qtwayland-5.15.18-0052-tests-fix-tst_xdgshell-minmaxsize.patch"
                         "qtwayland-5.15.18-0053-client-remove-some-surface-commits.patch"
                         "qtwayland-5.15.18-0054-client-avoid-locking-resizing-in-qwaylandshmbackings.patch"
-                        "qtwayland-5.15.18-0055-bradient-use-qwaylandwindow-actual-window-title.patch"))
+                        "qtwayland-5.15.18-0055-bradient-use-qwaylandwindow-actual-window-title.patch"
+                        "qtwayland-5.15.18-0056-redraw-hidpi.patch"))
               (sha256
                (base32
                 "07gqgd6ixqnsvc9r1c9y92vaxwj11ijrqvnxib8sv6xwhcmhvw43"))))