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  1. Qt
  2. QTBUG-138882

[Wayland] QWaylandShmBackingStore::scroll() is scrolling the busy buffer

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    • Icon: Bug Bug
    • Resolution: Fixed
    • Icon: P2: Important P2: Important
    • 6.10.0 RC
    • 6.10.0 Beta1, 6.10.0 Beta2
    • QPA: Wayland
    • None
    • Linux/Wayland
    • 1aa383378 (dev), 9eae9081b (6.10)

      When QWaylandShmBackingStore::scroll() is called by QtWidgets (it's called before the beginPaint()), the mBackBuffer is busy by the compositor, so Qt is scrolling the busy buffer.

      This code asserts:

      diff --git a/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp b/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
index 8698348db27..4a2825c00cd 100644
--- a/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
+++ b/src/plugins/platforms/wayland/qwaylandshmbackingstore.cpp
@@ -225,6 +225,8 @@ bool QWaylandShmBackingStore::scroll(const QRegion &region, int dx, int dy)
     if (!mBackBuffer)
         return false;
 
+    Q_ASSERT(!mBackBuffer->busy());
+
     QImage *backBufferImage = mBackBuffer->image();
     const qreal devicePixelRatio = backBufferImage->devicePixelRatio();

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