Uploaded image for project: 'Qt'
  1. Qt
  2. QTBUG-83917

QHighDpiScaling Code Structure for Qt 6

    XMLWordPrintable

    Details

    • Type: Task
    • Status: Reported
    • Priority: P4: Low
    • Resolution: Unresolved
    • Affects Version/s: None
    • Fix Version/s: Some future release
    • Component/s: GUI: High-DPI
    • Labels:
      None

      Description

      QHighDpiScaling implements the scaling between the device independent and native coordinate systems.

      Today, this is implemented in lower level QtGui / upper level of QPA (more details in option 0 below). The implementation has the following characteristics:

      • It's possible to maintain a platform plugin without specific knowledge about QHighDpiScaling
      • It's possible to maintain upper layers of Qt Gui (and above) without specific knowledge about QHighDpiScaling
      • The implementation is cross-platform, and can be tested/simulated on any platform.

      The code is isolated to a specific layer in the QtGui stack - at least to a certain degree. Is it possible to isolate it further?

      Option 0: (the current implementation)

      • Insert scaling calls when calling QPlatform* API
      • Insert scaling calls when creating QWindowSystemInterface events
      • Implement event handling code (related to QHighDpiScaling) in QGuiApplication

      Example pseudo-code:

      QRect QWindow::geometry() {
         return QHighDpiScaling::fromNative(
              platformWindow->geometry(), this);
      }
      void QWindow::setGeometry(QRect geometry) {
         platformWindow->setGeometry(
             QHighDpiScaling::toNative(geometry, this));
      }
      
      {code:java}
      QT_DEFINE_QPA_EVENT_HANDLER(bool, handleMouseEvent, window, pos) {
          auto *event = new QWindowSystemInterfacePrivate::MouseEvent(
              window, QHighDpi::fromNative(pos, window));
      }
      

      Option 1: Move QHighDpiScaling calls down to the QPA level

      • QPlatform* API returns geometry in device independent pixels - no scaling calls in QWindow.
      • Insert scaling calls when creating QWindowSystemInterface events
      • Implement event handling code (related to QHighDpiScaling) in the QWindowSystemInterface::handle* functions, instead of in QGuiApplication

      This creates a conflict: QPlatformWindow::geometry() now needs to perform the scaling, but is at the same time overridden by the platforms. One way to resolve this is to add new "public" QPlatformWindow API:

      QRect QPlatformWindow::deviceIndependentGeometry() {
          return QHighDpi::fromNative(this->geometry(), this);
      }
      

      QWindow then becomes:

      QRect QWindow::geometry() {
          return platformWindow->deviceIndependentGeometry();
      }
      

      Option 2: Move QHighDpiScaling calls down to the QPA level and leave geometry() untouched

      • QPlatform* API returns geometry in device independent pixels - no scaling calls in QWindow.
      • Limits dealing with scaling to platforms that need it
      QRect QWindowsWindow::geometry() {
          return QHighDpi::fromNative(m_nativeHandle->geometry(), this); // scaling needed 
      }
      
      QRect QCocoaWindow::geometry() {
          return m_nativeHandle->geometry(); // no scaling needed
      }
      
      QRect QWindow::geometry() {
          return platformWindow->geometry(); // no need to think about scaling, platform layer always reports device independent pixels, isolating the logic
      }
      

        Attachments

        No reviews matched the request. Check your Options in the drop-down menu of this sections header.

          Activity

            People

            Assignee:
            sorvig Morten Sørvig
            Reporter:
            sorvig Morten Sørvig
            Votes:
            0 Vote for this issue
            Watchers:
            1 Start watching this issue

              Dates

              Created:
              Updated:

                Gerrit Reviews

                There are no open Gerrit changes