plugins/screencast: send frame callbacks if the window is otherwise invisible

If we don't send frame callbacks, the application might stop rendering or
throttle to single digit fps.

BUG: 464217

src/plugins/screencast/windowscreencastsource.cpp

@@ -18,7 +18,6 @@
 #include "scene/itemrenderer.h"
 #include "scene/windowitem.h"
 #include "scene/workspacescene.h"
-#include "window.h"
 
 namespace KWin
 {
@@ -26,6 +25,7 @@ namespace KWin
 WindowScreenCastSource::WindowScreenCastSource(Window *window, QObject *parent)
     : ScreenCastSource(parent)
     , m_window(window)
+    , m_offscreenRef(window)
 {
     connect(m_window, &Window::windowClosed, this, &ScreenCastSource::closed);
 }

src/plugins/screencast/windowscreencastsource.h

@@ -7,14 +7,14 @@
 #pragma once
 
 #include "screencastsource.h"
+#include "window.h"
 
 #include <QPointer>
+#include <QTimer>
 
 namespace KWin
 {
 
-class Window;
-
 class WindowScreenCastSource : public ScreenCastSource
 {
     Q_OBJECT
@@ -31,6 +31,7 @@ public:
 
 private:
     QPointer<Window> m_window;
+    WindowOffscreenRenderRef m_offscreenRef;
 };
 
 } // namespace KWin

src/window.cpp

@@ -119,6 +119,7 @@ Window::Window()
     connect(Workspace::self()->applicationMenu(), &ApplicationMenu::applicationMenuEnabledChanged, this, [this] {
         Q_EMIT hasApplicationMenuChanged(hasApplicationMenu());
     });
+    connect(&m_offscreenFramecallbackTimer, &QTimer::timeout, this, &Window::maybeSendFrameCallback);
 }
 
 Window::~Window()
@@ -4537,6 +4538,45 @@ bool Window::isLockScreenOverlay() const
     return m_lockScreenOverlay;
 }
 
+void Window::refOffscreenRendering()
+{
+    if (m_offscreenRenderCount == 0) {
+        m_offscreenFramecallbackTimer.start(1'000'000 / output()->refreshRate());
+    }
+    m_offscreenRenderCount++;
+}
+
+void Window::unrefOffscreenRendering()
+{
+    Q_ASSERT(m_offscreenRenderCount);
+    m_offscreenRenderCount--;
+    if (m_offscreenRenderCount == 0) {
+        m_offscreenFramecallbackTimer.stop();
+    }
+}
+
+void Window::maybeSendFrameCallback()
+{
+    if (m_surface && !m_windowItem->isVisible()) {
+        m_surface->frameRendered(std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count());
+        // update refresh rate, it might have changed
+        m_offscreenFramecallbackTimer.start(1'000'000 / output()->refreshRate());
+    }
+}
+
+WindowOffscreenRenderRef::WindowOffscreenRenderRef(Window *window)
+    : m_window(window)
+{
+    window->refOffscreenRendering();
+}
+
+WindowOffscreenRenderRef::~WindowOffscreenRenderRef()
+{
+    if (m_window) {
+        m_window->unrefOffscreenRendering();
+    }
+}
+
 } // namespace KWin
 
 #include "moc_window.cpp"

src/window.h

@@ -27,6 +27,7 @@
 #include <QObject>
 #include <QPointer>
 #include <QRectF>
+#include <QTimer>
 #include <QUuid>
 
 class QMouseEvent;
@@ -1429,6 +1430,9 @@ public:
 
     void setTile(Tile *tile);
 
+    void refOffscreenRendering();
+    void unrefOffscreenRendering();
+
 public Q_SLOTS:
     virtual void closeWindow() = 0;
 
@@ -1913,6 +1917,8 @@ private Q_SLOTS:
     void shadeUnhover();
 
 private:
+    void maybeSendFrameCallback();
+
     // when adding new data members, check also copyToDeleted()
     QUuid m_internalId;
     Xcb::Window m_client;
@@ -2029,6 +2035,8 @@ private:
     WindowRules m_rules;
     quint32 m_lastUsageSerial = 0;
     bool m_lockScreenOverlay = false;
+    uint32_t m_offscreenRenderCount = 0;
+    QTimer m_offscreenFramecallbackTimer;
 };
 
 /**
@@ -2375,6 +2383,17 @@ inline void Window::setPendingMoveResizeMode(MoveResizeMode mode)
 
 KWIN_EXPORT QDebug operator<<(QDebug debug, const Window *window);
 
+class KWIN_EXPORT WindowOffscreenRenderRef
+{
+public:
+    WindowOffscreenRenderRef(Window *window);
+    WindowOffscreenRenderRef() = default;
+    ~WindowOffscreenRenderRef();
+
+private:
+    QPointer<Window> m_window;
+};
+
 } // namespace KWin
 
 Q_DECLARE_METATYPE(KWin::Window *)