Introduce DamageJournal helper

src/platformsupport/scenes/opengl/openglbackend.cpp

@@ -35,30 +35,6 @@ void OpenGLBackend::setFailed(const QString &reason)
     m_failed = true;
 }
 
-void OpenGLBackend::addToDamageHistory(const QRegion &region)
-{
-    if (m_damageHistory.count() > 10)
-        m_damageHistory.removeLast();
-
-    m_damageHistory.prepend(region);
-}
-
-QRegion OpenGLBackend::accumulatedDamageHistory(int bufferAge) const
-{
-    QRegion region;
-
-    // Note: An age of zero means the buffer contents are undefined
-    if (bufferAge > 0 && bufferAge <= m_damageHistory.count()) {
-        for (int i = 0; i < bufferAge - 1; i++)
-            region |= m_damageHistory[i];
-    } else {
-        const QSize &s = screens()->size();
-        region = QRegion(0, 0, s.width(), s.height());
-    }
-
-    return region;
-}
-
 OverlayWindow* OpenGLBackend::overlayWindow() const
 {
     return nullptr;

src/platformsupport/scenes/opengl/openglbackend.h

@@ -129,16 +129,6 @@ public:
     }
     virtual bool directScanoutAllowed(int screen) const;
 
-    /**
-     * Returns the damage that has accumulated since a buffer of the given age was presented.
-     */
-    QRegion accumulatedDamageHistory(int bufferAge) const;
-
-    /**
-     * Saves the given region to damage history.
-     */
-    void addToDamageHistory(const QRegion &region);
-
     /**
      * The backend specific extensions (e.g. EGL/GLX extensions).
      *
@@ -244,10 +234,6 @@ private:
      * @brief Whether the initialization failed, of course default to @c false.
      */
     bool m_failed;
-    /**
-     * @brief The damage history for the past 10 frames.
-     */
-    QList<QRegion> m_damageHistory;
     QList<QByteArray> m_extensions;
 };
 

src/plugins/platforms/drm/egl_gbm_backend.cpp

@@ -528,20 +528,13 @@ QRegion EglGbmBackend::prepareRenderingForOutput(Output &output)
     }
     setViewport(output);
 
+    const QRect geometry = output.output->geometry();
     if (supportsBufferAge()) {
-        QRegion region;
-
-        // Note: An age of zero means the buffer contents are undefined
-        if (output.current.bufferAge > 0 && output.current.bufferAge <= output.current.damageHistory.count()) {
-            for (int i = 0; i < output.current.bufferAge - 1; i++)
-                region |= output.current.damageHistory[i];
-        } else {
-            region = output.output->geometry();
-        }
-
-        return region;
+        auto current = &output.current;
+        return current->damageJournal.accumulate(current->bufferAge, geometry);
     }
-    return output.output->geometry();
+
+    return geometry;
 }
 
 QSharedPointer<DrmBuffer> EglGbmBackend::endFrameWithBuffer(int screenId, const QRegion &dirty)
@@ -581,10 +574,7 @@ void EglGbmBackend::updateBufferAge(Output &output, const QRegion &dirty)
 {
     if (supportsBufferAge()) {
         eglQuerySurface(eglDisplay(), output.current.gbmSurface->eglSurface(), EGL_BUFFER_AGE_EXT, &output.current.bufferAge);
-        if (output.current.damageHistory.count() > 10) {
-            output.current.damageHistory.removeLast();
-        }
-        output.current.damageHistory.prepend(dirty);
+        output.current.damageJournal.add(dirty);
     }
 }
 
@@ -665,7 +655,7 @@ bool EglGbmBackend::scanout(int screenId, SurfaceItem *surfaceItem)
     // ensure that a context is current like with normal presentation
     makeCurrent();
     if (output.output->present(bo, damage)) {
-        output.current.damageHistory.clear();
+        output.current.damageJournal.clear();
         if (output.surfaceInterface != surface) {
             auto path = surface->client()->executablePath();
             qCDebug(KWIN_DRM).nospace() << "Direct scanout starting on output " << output.output->name() << " for application \"" << path << "\"";

src/plugins/platforms/drm/egl_gbm_backend.h

@@ -9,6 +9,7 @@
 #ifndef KWIN_EGL_GBM_BACKEND_H
 #define KWIN_EGL_GBM_BACKEND_H
 #include "abstract_egl_drm_backend.h"
+#include "utils.h"
 
 #include <kwinglutils.h>
 
@@ -87,10 +88,7 @@ private:
             QSharedPointer<ShadowBuffer> shadowBuffer;
             QSharedPointer<GbmSurface> gbmSurface;
             int bufferAge = 0;
-            /**
-            * @brief The damage history for the past 10 frames.
-            */
-            QList<QRegion> damageHistory;
+            DamageJournal damageJournal;
 
             // for secondary GPU import
             ImportMode importMode = ImportMode::Dmabuf;

src/plugins/platforms/x11/standalone/eglbackend.cpp

@@ -98,8 +98,9 @@ QRegion EglBackend::beginFrame(int screenId)
     glViewport(0, 0, size.width(), size.height());
 
     QRegion repaint;
-    if (supportsBufferAge())
-        repaint = accumulatedDamageHistory(m_bufferAge);
+    if (supportsBufferAge()) {
+        repaint = m_damageJournal.accumulate(m_bufferAge, screens()->geometry());
+    }
 
     eglWaitNative(EGL_CORE_NATIVE_ENGINE);
 
@@ -122,7 +123,7 @@ void EglBackend::endFrame(int screenId, const QRegion &renderedRegion, const QRe
 
     // Save the damaged region to history
     if (supportsBufferAge()) {
-        addToDamageHistory(damagedRegion);
+        m_damageJournal.add(damagedRegion);
     }
 }
 

src/plugins/platforms/x11/standalone/eglbackend.h

@@ -40,6 +40,7 @@ private:
 
     X11StandalonePlatform *m_backend;
     SoftwareVsyncMonitor *m_vsyncMonitor;
+    DamageJournal m_damageJournal;
     int m_bufferAge = 0;
 };
 

src/plugins/platforms/x11/standalone/glxbackend.cpp

@@ -746,8 +746,9 @@ QRegion GlxBackend::beginFrame(int screenId)
     const QSize size = screens()->size();
     glViewport(0, 0, size.width(), size.height());
 
-    if (supportsBufferAge())
-        repaint = accumulatedDamageHistory(m_bufferAge);
+    if (supportsBufferAge()) {
+        repaint = m_damageJournal.accumulate(m_bufferAge, screens()->geometry());
+    }
 
     glXWaitX();
 
@@ -770,8 +771,9 @@ void GlxBackend::endFrame(int screenId, const QRegion &renderedRegion, const QRe
         overlayWindow()->show();   // since that pass may take long
 
     // Save the damaged region to history
-    if (supportsBufferAge())
-        addToDamageHistory(damagedRegion);
+    if (supportsBufferAge()) {
+        m_damageJournal.add(damagedRegion);
+    }
 }
 
 void GlxBackend::vblank(std::chrono::nanoseconds timestamp)

src/plugins/platforms/x11/standalone/glxbackend.h

@@ -106,6 +106,7 @@ private:
     QHash<xcb_visualid_t, FBConfigInfo *> m_fbconfigHash;
     QHash<xcb_visualid_t, int> m_visualDepthHash;
     std::unique_ptr<SwapEventFilter> m_swapEventFilter;
+    DamageJournal m_damageJournal;
     int m_bufferAge;
     bool m_haveMESACopySubBuffer = false;
     bool m_haveMESASwapControl = false;

src/utils.h

@@ -210,6 +210,73 @@ protected:
 #endif
 };
 
+/**
+ * The DamageJournal class is a helper that tracks last N damage regions.
+ */
+class KWIN_EXPORT DamageJournal
+{
+public:
+    /**
+     * Returns the maximum number of damage regions that can be stored in the journal.
+     */
+    int capacity() const
+    {
+        return m_capacity;
+    }
+
+    /**
+     * Sets the maximum number of damage regions that can be stored in the journal
+     * to @a capacity.
+     */
+    void setCapacity(int capacity)
+    {
+        m_capacity = capacity;
+    }
+
+    /**
+     * Adds the specified @a region to the journal.
+     */
+    void add(const QRegion &region)
+    {
+        while (m_log.size() >= m_capacity) {
+            m_log.takeLast();
+        }
+        m_log.prepend(region);
+    }
+
+    /**
+     * Clears the damage journal. Typically, one would want to clear the damage journal
+     * if a buffer swap fails for some reason.
+     */
+    void clear()
+    {
+        m_log.clear();
+    }
+
+    /**
+     * Accumulates the damage regions in the log up to the specified @a bufferAge.
+     *
+     * If the specified buffer age value refers to a damage region older than the last
+     * one in the journal, @a fallback will be returned.
+     */
+    QRegion accumulate(int bufferAge, const QRegion &fallback = QRegion()) const
+    {
+        QRegion region;
+        if (bufferAge > 0 && bufferAge <= m_log.size()) {
+            for (int i = 0; i < bufferAge - 1; ++i) {
+                region |= m_log[i];
+            }
+        } else {
+            region = fallback;
+        }
+        return region;
+    }
+
+private:
+    QList<QRegion> m_log;
+    int m_capacity = 10;
+};
+
 } // namespace
 
 // Must be outside namespace