[libkwineffects] Gracefully release previous window pixmap

Summary:
If the cross fade animation is cancelled, we are not gracefully
unreference the previous window pixmap.

This change addresses that issue by using RAII approach to
reference/unreference the previous window pixmap.

Test Plan: Manually. The Maximize and the Morphing Popups effect still work.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16391

libkwineffects/anidata.cpp

@@ -52,6 +52,21 @@ KeepAliveLock::~KeepAliveLock()
     m_window->unrefWindow();
 }
 
+PreviousWindowPixmapLock::PreviousWindowPixmapLock(EffectWindow *w)
+    : m_window(w)
+{
+    m_window->referencePreviousWindowPixmap();
+}
+
+PreviousWindowPixmapLock::~PreviousWindowPixmapLock()
+{
+    m_window->unreferencePreviousWindowPixmap();
+
+    // Add synthetic repaint to prevent glitches after cross-fading
+    // translucent windows.
+    effects->addRepaint(m_window->expandedGeometry());
+}
+
 AniData::AniData()
  : attribute(AnimationEffect::Opacity)
  , customCurve(0) // Linear
@@ -67,7 +82,8 @@ AniData::AniData()
 
 AniData::AniData(AnimationEffect::Attribute a, int meta_, int ms, const FPx2 &to_,
                  QEasingCurve curve_, int delay, const FPx2 &from_, bool waitAtSource_, bool keepAtTarget_,
-                 FullScreenEffectLockPtr fullScreenEffectLock_, bool keepAlive)
+                 FullScreenEffectLockPtr fullScreenEffectLock_, bool keepAlive,
+                 PreviousWindowPixmapLockPtr previousWindowPixmapLock_)
  : attribute(a)
  , curve(curve_)
  , from(from_)
@@ -80,6 +96,7 @@ AniData::AniData(AnimationEffect::Attribute a, int meta_, int ms, const FPx2 &to
  , waitAtSource(waitAtSource_)
  , keepAtTarget(keepAtTarget_)
  , keepAlive(keepAlive)
+ , previousWindowPixmapLock(previousWindowPixmapLock_)
 {
 }
 

libkwineffects/anidata_p.h

@@ -56,13 +56,28 @@ private:
 };
 typedef QSharedPointer<KeepAliveLock> KeepAliveLockPtr;
 
+/**
+ * References the previous window pixmap to prevent discarding.
+ **/
+class PreviousWindowPixmapLock
+{
+public:
+    PreviousWindowPixmapLock(EffectWindow *w);
+    ~PreviousWindowPixmapLock();
+
+private:
+    EffectWindow *m_window;
+    Q_DISABLE_COPY(PreviousWindowPixmapLock)
+};
+typedef QSharedPointer<PreviousWindowPixmapLock> PreviousWindowPixmapLockPtr;
+
 class KWINEFFECTS_EXPORT AniData {
 public:
     AniData();
     AniData(AnimationEffect::Attribute a, int meta, int ms, const FPx2 &to,
             QEasingCurve curve, int delay, const FPx2 &from, bool waitAtSource,
             bool keepAtTarget = false, FullScreenEffectLockPtr=FullScreenEffectLockPtr(),
-            bool keepAlive = true);
+            bool keepAlive = true, PreviousWindowPixmapLockPtr previousWindowPixmapLock = {});
     inline void addTime(int t) { time += t; }
     inline bool isOneDimensional() const {
         return from[0] == from[1] && to[0] == to[1];
@@ -81,6 +96,7 @@ public:
     bool waitAtSource, keepAtTarget;
     bool keepAlive;
     KeepAliveLockPtr keepAliveLock;
+    PreviousWindowPixmapLockPtr previousWindowPixmapLock;
 };
 
 } // namespace

libkwineffects/kwinanimationeffect.cpp

@@ -220,8 +220,6 @@ quint64 AnimationEffect::p_animate( EffectWindow *w, Attribute a, uint meta, int
 {
     const bool waitAtSource = from.isValid();
     validate(a, meta, &from, &to, w);
-    if (a == CrossFadePrevious)
-        w->referencePreviousWindowPixmap();
 
     Q_D(AnimationEffect);
     if (!d->m_isInitialized)
@@ -247,7 +245,27 @@ quint64 AnimationEffect::p_animate( EffectWindow *w, Attribute a, uint meta, int
             fullscreen = d->m_fullScreenEffectLock.toStrongRef();
         }
     }
-    it->first.append(AniData(a, meta, ms, to, curve, delay, from, waitAtSource, keepAtTarget, fullscreen, keepAlive));
+
+    PreviousWindowPixmapLockPtr previousPixmap;
+    if (a == CrossFadePrevious) {
+        previousPixmap = PreviousWindowPixmapLockPtr::create(w);
+    }
+
+    it->first.append(AniData(
+        a,              // Attribute
+        meta,           // Metadata
+        ms,             // Duration
+        to,             // Target
+        curve,          // Easing curve
+        delay,          // Delay
+        from,           // Source
+        waitAtSource,   // Whether the animation should be kept at source
+        keepAtTarget,   // Whether the animation is persistent
+        fullscreen,     // Full screen effect lock
+        keepAlive,      // Keep alive flag
+        previousPixmap  // Previous window pixmap lock
+    ));
+
     quint64 ret_id = ++d->m_animCounter;
     it->first.last().id = ret_id;
     it->second = QRect();
@@ -344,11 +362,6 @@ void AnimationEffect::prePaintScreen( ScreenPrePaintData& data, int time )
                 ++animCounter;
             } else {
                 EffectWindow *oldW = entry.key();
-                AniData *aData = &(*anim);
-                if (aData->attribute == KWin::AnimationEffect::CrossFadePrevious) {
-                    oldW->unreferencePreviousWindowPixmap();
-                    effects->addRepaint(oldW->expandedGeometry());
-                }
                 d->m_justEndedAnimation = anim->id;
                 animationEnded(oldW, anim->attribute, anim->meta);
                 d->m_justEndedAnimation = 0;