qt: add base window classes for compositors

CompositorOffscreenWindow allows to fake making the window visible without
instantiating it

DummyRenderWindow is a simple window that doesn't draw anything, as using a bare
QWindow on Linux makes the window freeze while resizing

modules/gui/qt/Makefile.am

@@ -164,6 +164,8 @@ libqt_plugin_la_SOURCES = \
 	gui/qt/dialogs/playlists/playlists.cpp gui/qt/dialogs/playlists/playlists.hpp \
 	gui/qt/maininterface/compositor.hpp \
 	gui/qt/maininterface/compositor.cpp \
+	gui/qt/maininterface/compositor_common.hpp \
+	gui/qt/maininterface/compositor_common.cpp \
 	gui/qt/maininterface/compositor_dummy.hpp \
 	gui/qt/maininterface/compositor_dummy.cpp \
 	gui/qt/maininterface/interface_window_handler.cpp \
@@ -440,6 +442,7 @@ nodist_libqt_plugin_la_SOURCES = \
 	gui/qt/dialogs/toolbar/controlbar_profile_model.moc.cpp \
 	gui/qt/dialogs/playlists/playlists.moc.cpp \
 	gui/qt/maininterface/compositor.moc.cpp \
+	gui/qt/maininterface/compositor_common.moc.cpp \
 	gui/qt/maininterface/compositor_dummy.moc.cpp \
 	gui/qt/maininterface/interface_window_handler.moc.cpp \
 	gui/qt/maininterface/mainctx.moc.cpp \

modules/gui/qt/maininterface/compositor_common.cpp

@@ -0,0 +1,172 @@
+/*****************************************************************************
+ * Copyright (C) 2023 VLC authors and VideoLAN
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+
+#include "compositor_common.hpp"
+
+#include <QBackingStore>
+#ifndef QT_NO_ACCESSIBILITY
+#include <QAccessible>
+#endif
+
+#ifdef QT5_DECLARATIVE_PRIVATE
+#include <private/qquickwindow_p.h>
+#endif
+
+using namespace vlc;
+
+DummyRenderWindow::DummyRenderWindow(QWindow* parent)
+    : QWindow(parent)
+{
+    setSurfaceType(RasterSurface);
+    QSurfaceFormat fmt = format();
+    fmt.setAlphaBufferSize(8);
+    setFormat(fmt);
+}
+
+QAccessibleInterface* DummyRenderWindow::accessibleRoot() const
+{
+#ifndef QT_NO_ACCESSIBILITY
+    QAccessibleInterface* iface = QAccessible::queryAccessibleInterface(
+                const_cast<DummyRenderWindow*>(this));
+    return iface;
+#else
+    return nullptr;
+#endif
+}
+
+bool DummyRenderWindow::event(QEvent* event)
+{
+    switch (event->type() )
+    {
+    case QEvent::UpdateRequest:
+        render();
+        return true;
+    case QEvent::Expose:
+        if (isExposed())
+            requestUpdate();
+        return true;
+    default:
+        break;
+    }
+
+    return QWindow::event(event);
+}
+
+void DummyRenderWindow::resizeEvent(QResizeEvent* resizeEvent)
+{
+    if (!m_backingStore)
+        return;
+    if (!m_initialized)
+        init();
+    m_backingStore->resize(resizeEvent->size());
+}
+
+void DummyRenderWindow::init()
+{
+    if (m_initialized)
+        return;
+    m_initialized = true;
+    m_backingStore = new QBackingStore(this);
+}
+
+void DummyRenderWindow::render()
+{
+    if (!m_initialized)
+        init();
+    if (!isExposed())
+        return;
+    QRect rect(0, 0, width(), height());
+    if (m_backingStore->size() != size())
+    {
+        m_backingStore->resize(size());
+    }
+
+    //note that we don't need to actually use our backing store
+    //drawing anything would just lead to flickering
+    m_backingStore->flush(QRect(0, 0, 1, 1));
+    return;
+}
+
+#ifdef QT5_DECLARATIVE_PRIVATE
+
+class OffscreenWindowPrivate: public QQuickWindowPrivate
+{
+public:
+    void setVisible(bool newVisible) override {
+        Q_Q(QWindow);
+        if (visible != newVisible)
+        {
+            visible = newVisible;
+            q->visibleChanged(newVisible);
+            // this stays always invisible
+            visibility = newVisible ? QWindow::Windowed : QWindow::Hidden;
+            q->visibilityChanged(visibility); // workaround for QTBUG-49054
+        }
+    }
+};
+
+CompositorOffscreenWindow::CompositorOffscreenWindow(QQuickRenderControl* renderControl)
+    : QQuickWindow(* (new OffscreenWindowPrivate()), renderControl)
+{
+}
+
+static Qt::WindowState resolveWindowState(Qt::WindowStates states)
+{
+    // No more than one of these 3 can be set
+    if (states & Qt::WindowMinimized)
+        return Qt::WindowMinimized;
+    if (states & Qt::WindowMaximized)
+        return Qt::WindowMaximized;
+    if (states & Qt::WindowFullScreen)
+        return Qt::WindowFullScreen;
+    // No state means "windowed" - we ignore Qt::WindowActive
+    return Qt::WindowNoState;
+}
+
+void CompositorOffscreenWindow::setWindowStateExt(Qt::WindowState state)
+{
+    QWindow::setWindowState(resolveWindowState(state));
+}
+
+void CompositorOffscreenWindow::setPseudoVisible(bool visible)
+{
+    setVisible(visible);
+}
+
+#else
+
+CompositorOffscreenWindow::CompositorOffscreenWindow(QQuickRenderControl* renderControl)
+: QQuickWindow(renderControl)
+{
+}
+
+void CompositorOffscreenWindow::setWindowStateExt(Qt::WindowState state)
+{
+    QWindow::setWindowState(state);
+}
+
+//don't set the window visible, this would create the window, and show make it actually visible
+void CompositorOffscreenWindow::setPseudoVisible(bool)
+{
+}
+
+#endif
+
+
+

modules/gui/qt/maininterface/compositor_common.hpp

@@ -0,0 +1,74 @@
+/*****************************************************************************
+ * Copyright (C) 2023 VLC authors and VideoLAN
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifndef COMPOSITOR_COMMON_HPP
+#define COMPOSITOR_COMMON_HPP
+
+#include <QWindow>
+#include <QQuickWindow>
+
+namespace vlc {
+
+/**
+ * a minimal window with no content
+ * this may be useful on linux platform to provide a
+ * window which can be drawn into, using a bare QWindow
+ * usually freeze on resize
+ */
+class DummyRenderWindow : public QWindow
+{
+    Q_OBJECT
+public:
+    explicit DummyRenderWindow(QWindow* parent = nullptr);
+
+    virtual QAccessibleInterface *accessibleRoot() const override;
+
+protected:
+    bool event(QEvent *event) override;
+
+    void resizeEvent(QResizeEvent *resizeEvent) override;
+
+private:
+    void init();
+    void render();
+
+    QBackingStore* m_backingStore = nullptr;
+    bool m_initialized = false;;
+};
+
+
+/**
+ * @brief The CompositorOffscreenWindow class allows to fake the visiblilty
+ * of the the QQuickWindow, note that this feature will only work if QT5_DECLARATIVE_PRIVATE
+ * are available
+ */
+class CompositorOffscreenWindow : public QQuickWindow
+{
+    Q_OBJECT
+public:
+    explicit CompositorOffscreenWindow(QQuickRenderControl* renderControl);
+
+    void setWindowStateExt(Qt::WindowState);
+
+    void setPseudoVisible(bool visible);
+};
+
+
+}
+
+#endif /* COMPOSITOR_COMMON_HPP */

modules/gui/qt/meson.build

@@ -65,6 +65,7 @@ moc_headers = files(
     'dialogs/playlists/playlists.hpp',
     'dialogs/vlm/vlm.hpp',
     'maininterface/compositor.hpp',
+    'maininterface/compositor_common.hpp',
     'maininterface/compositor_dummy.hpp',
     'maininterface/interface_window_handler.hpp',
     'maininterface/mainctx.hpp',
@@ -272,6 +273,8 @@ some_sources = files(
     'dialogs/playlists/playlists.hpp',
     'maininterface/compositor.hpp',
     'maininterface/compositor.cpp',
+    'maininterface/compositor_common.hpp',
+    'maininterface/compositor_common.cpp',
     'maininterface/compositor_dummy.hpp',
     'maininterface/compositor_dummy.cpp',
     'maininterface/interface_window_handler.cpp',