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  1. Qt
  2. QTBUG-88562

In the case of multiple screen and scale ratio greater than 1, the global mouse coordinates are wrong

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    • Platform/s:
      Linux/Wayland

      Description

      As we know the QCursor::pos is transformed by QPlatformCursor::pos() like this

      QPoint QCursor::pos(const QScreen *screen)
      {
      if (screen) {
      if (const QPlatformCursor *cursor = screen->handle()->cursor())

      Unknown macro: { const QPlatformScreen *ps = screen->handle(); QPoint nativePos = cursor->pos(); ps = ps->screenForPosition(nativePos); return QHighDpi}

      }
      return QGuiApplicationPrivate::lastCursorPosition.toPoint();
      }

      In QtWayland the QWaylandCursor::pointerEvent effect QWaylandCursor::pos

      void QWaylandCursor::pointerEvent(const QMouseEvent &event)

      Unknown macro: { mLastPos = event.globalPos(); }

      QPoint QWaylandCursor::pos() const

      Unknown macro: { return mLastPos; }

      The QWaylandCursor::pointerEvent is Used in QGuiApplicationPrivate::processMouseEvent

      void QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent *e)
      {
      ......
      #ifndef QT_NO_CURSOR
      if (!e->synthetic()) {
      if (const QScreen *screen = window->screen())
      if (QPlatformCursor *cursor = screen->handle()->cursor())

      Unknown macro: { const QPointF nativeLocalPoint = QHighDpi}

      }
      #endif
      ......
      }

      Based on the following conditions :
      1. multiple screen
      2. The window is displayed between two screens
      3. The window's scale ratio is 1.5(QT_SCALE_FACTOR=1.5 or QPlatformScreen::logicDpi = 144)
      4. The mouse pointer is on window and in second screen
      5. Suppose the physical size of the two screens is 1920*1080

      Based on the above conditions to calculate QCursor::pos :
      1. QGuiApplicationPrivate::processMouseEvent e->globalPos = (1500, 200)
      2. const QPointF nativeGlobalPoint = QHighDpi::toNativePixels(globalPoint, screen) = (2250, 300)
      3. cursor->pointerEvent(ev) -> QWaylandCursor::pos = (2250, 150)
      4. QWaylandCursor::pos = (2250, 150) -> QCursor::pos = (2140, 150)

      Calculation error in the second step, becase of toNativePixels's calculation methods.

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            Assignee:
            michealchen Chen Gong
            Reporter:
            michealchen Chen Gong
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              Created:
              Updated:
              Resolved:

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