From f85e34a3e99038d3fd2c939f3bf7355f4f2df4a3 Mon Sep 17 00:00:00 2001
From: "Uwe L. Korn" <uwelk@xhochy.com>
Date: Sun, 12 Oct 2014 11:29:44 +0100
Subject: [PATCH] Memoize visibility filter

---
 .../playlist/PlayableProxyModel.cpp           | 30 ++++++++++++-------
 src/libtomahawk/playlist/PlayableProxyModel.h | 20 +++++++++++--
 2 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/src/libtomahawk/playlist/PlayableProxyModel.cpp b/src/libtomahawk/playlist/PlayableProxyModel.cpp
index 88d521d86..e58aafc00 100644
--- a/src/libtomahawk/playlist/PlayableProxyModel.cpp
+++ b/src/libtomahawk/playlist/PlayableProxyModel.cpp
@@ -145,20 +145,22 @@ PlayableProxyModel::setSourcePlayableModel( PlayableModel* sourceModel )
 bool
 PlayableProxyModel::filterAcceptsRow( int sourceRow, const QModelIndex& sourceParent ) const
 {
+    PlayableProxyModelFilterMemo memo;
+
     PlayableItem* pi = itemFromIndex( sourceModel()->index( sourceRow, 0, sourceParent ) );
     if ( !pi )
         return false;
 
-    return filterAcceptsRowInternal( sourceRow, pi, sourceParent );
+    return filterAcceptsRowInternal( sourceRow, pi, sourceParent, memo );
 }
 
 
 bool
-PlayableProxyModel::filterAcceptsRowInternal( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent ) const
+PlayableProxyModel::filterAcceptsRowInternal( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent, PlayableProxyModelFilterMemo& memo ) const
 {
-    if ( m_maxVisibleItems > 0 && !visibilityFilterAcceptsRow( sourceRow, sourceParent ) )
+    if ( m_maxVisibleItems > 0 && !visibilityFilterAcceptsRow( sourceRow, sourceParent, memo ) )
         return false;
-    if ( m_hideDupeItems && !dupeFilterAcceptsRow( sourceRow, pi, sourceParent ) )
+    if ( m_hideDupeItems && !dupeFilterAcceptsRow( sourceRow, pi, sourceParent, memo ) )
         return false;
 
     return nameFilterAcceptsRow( sourceRow, pi, sourceParent );
@@ -166,7 +168,7 @@ PlayableProxyModel::filterAcceptsRowInternal( int sourceRow, PlayableItem* pi, c
 
 
 bool
-PlayableProxyModel::dupeFilterAcceptsRow( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent ) const
+PlayableProxyModel::dupeFilterAcceptsRow( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent, PlayableProxyModelFilterMemo& memo ) const
 {
     if ( !m_hideDupeItems )
         return true;
@@ -181,7 +183,7 @@ PlayableProxyModel::dupeFilterAcceptsRow( int sourceRow, PlayableItem* pi, const
                  ( pi->album() && pi->album() == di->album() ) ||
                  ( pi->artist() && pi->artist()->name() == di->artist()->name() );
 
-        if ( b && filterAcceptsRowInternal( i, di, sourceParent ) )
+        if ( b && filterAcceptsRowInternal( i, di, sourceParent, memo ) )
             return false;
     }
 
@@ -190,18 +192,26 @@ PlayableProxyModel::dupeFilterAcceptsRow( int sourceRow, PlayableItem* pi, const
 
 
 bool
-PlayableProxyModel::visibilityFilterAcceptsRow( int sourceRow, const QModelIndex& sourceParent ) const
+PlayableProxyModel::visibilityFilterAcceptsRow( int sourceRow, const QModelIndex& sourceParent, PlayableProxyModelFilterMemo& memo ) const
 {
     if ( m_maxVisibleItems <= 0 )
         return true;
 
-    int items = 0;
-    for ( int i = 0; ( i < sourceRow ) && ( items < m_maxVisibleItems ) ; i++ )
+    if ( static_cast<size_t>( sourceRow ) < memo.visibilty.size() )
+    {
+        // We have already memoized the return value.
+        return memo.visibilty[sourceRow] < m_maxVisibleItems;
+    }
+
+    int items = memo.visibilty.back();
+    for ( int i = memo.visibilty.size() - 1; ( i < sourceRow ) && ( items < m_maxVisibleItems ) ; i++ )
     {
         PlayableItem* pi = itemFromIndex( sourceModel()->index( i, 0, sourceParent ) );
-        if ( pi && dupeFilterAcceptsRow( i, pi, sourceParent ) && nameFilterAcceptsRow( i, pi, sourceParent ) )
+        // We will not change memo in these calls as all values needed in them are already memoized.
+        if ( pi && dupeFilterAcceptsRow( i, pi, sourceParent, memo ) && nameFilterAcceptsRow( i, pi, sourceParent ) )
         {
             items++;
+            memo.visibilty.push_back( items ); // Sets memo.visibilty[i + 1] to items
         }
     }
 
diff --git a/src/libtomahawk/playlist/PlayableProxyModel.h b/src/libtomahawk/playlist/PlayableProxyModel.h
index 9adc0aa93..86a92dceb 100644
--- a/src/libtomahawk/playlist/PlayableProxyModel.h
+++ b/src/libtomahawk/playlist/PlayableProxyModel.h
@@ -27,6 +27,20 @@
 
 #include "DllMacro.h"
 
+class PlayableProxyModelFilterMemo
+{
+public:
+    PlayableProxyModelFilterMemo()
+    {
+        // First element always has no predecessors.
+        // TODO C++11: Make this a constexpr using initializer lists.
+        visibilty.push_back( 0 );
+    }
+
+    virtual ~PlayableProxyModelFilterMemo() {}
+    std::vector<int> visibilty;
+};
+
 class DLLEXPORT PlayableProxyModel : public QSortFilterProxyModel
 {
 Q_OBJECT
@@ -117,10 +131,10 @@ private slots:
     void onCurrentIndexChanged( const QModelIndex& newIndex, const QModelIndex& oldIndex );
 
 private:
-    bool filterAcceptsRowInternal( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent ) const;
+    bool filterAcceptsRowInternal( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent, PlayableProxyModelFilterMemo& memo ) const;
     bool nameFilterAcceptsRow( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent ) const;
-    bool dupeFilterAcceptsRow( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent ) const;
-    bool visibilityFilterAcceptsRow( int sourceRow, const QModelIndex& sourceParent ) const;
+    bool dupeFilterAcceptsRow( int sourceRow, PlayableItem* pi, const QModelIndex& sourceParent, PlayableProxyModelFilterMemo& memo ) const;
+    bool visibilityFilterAcceptsRow( int sourceRow, const QModelIndex& sourceParent, PlayableProxyModelFilterMemo& memo ) const;
     bool lessThan( int column, const Tomahawk::query_ptr& left, const Tomahawk::query_ptr& right ) const;
 
     PlayableModel* m_model;