diff -r 89c329efa980 -r e48454f237ca ganeswidgets/src/HgScrollBufferManager.cpp
--- a/ganeswidgets/src/HgScrollBufferManager.cpp	Mon Apr 19 14:40:06 2010 +0300
+++ b/ganeswidgets/src/HgScrollBufferManager.cpp	Mon May 03 13:32:54 2010 +0300
@@ -216,145 +216,368 @@
         mTotalCount-1 : mBufferPosition+mBufferSize;
 }
 
-void HgScrollBufferManager::removeItems(int start, int end, int totalCount)
+void HgScrollBufferManager::addItems(int start, int end)
 {
-    int oldTotalCount = mTotalCount;
-    mTotalCount = totalCount;
+    FUNC_LOG;
+
+    mTotalCount += (end-start+1);
+    int lastBufferItem = mBufferPosition+mBufferSize-1;
 
-    if (isInsideBuffer(start, end)) {
-        if (mTotalCount > mBufferSize && mBufferPosition+mBufferSize == oldTotalCount) {
-            // We are at the end of items, move buffer
-            int oldBufferPos = mBufferPosition;
-            mBufferPosition = qMax(0, totalCount-mBufferSize);
+    if (start < mBufferPosition) {
+        simpleAddItems(start, end);
+        // New items push the buffer forward, items inside the buffer do not change
+    }
+    // Check buffer higher limit
+    else if (start <= lastBufferItem && end > lastBufferItem) {
+        simpleAddItems(start, lastBufferItem);
+        // Items added after the buffer are ignored
+    }
+    else {
+        simpleAddItems(start, end);
+    }
+}
+
+void HgScrollBufferManager::removeItems(int start, int end)
+{
+    FUNC_LOG;
+
+    int lastBufferItem = mBufferPosition+mBufferSize-1;
+    int removedItemCount = end-start+1;
 
-            if (start < oldBufferPos) { // Removed items are partially inside buffer
-                emit requestItems(mBufferPosition, start-1);
-            }
-            else {
-                emit requestItems(mBufferPosition, oldBufferPos-1);
-            }
-        }
-        else {
-            int first = qBound(mBufferPosition, start, mBufferPosition+mBufferSize-1);
-            int last = qBound(mBufferPosition, end, mBufferPosition+mBufferSize-1);
+    if (mTotalCount < mBufferSize) {
+        // Do nothing
+    }
+    else if (start > lastBufferItem) {
+        // Do nothing
+    }
+    else if (end < mBufferPosition) {
+        mTotalCount = mTotalCount-removedItemCount;
+        simpleRemoveItems(start, end);
+    }
+    else if (start < mBufferPosition && end > lastBufferItem) {
+        mTotalCount = mTotalCount-removedItemCount;
+        mBufferPosition = qBound(0, mBufferPosition, mTotalCount-mBufferSize);
+        resetBuffer(mBufferPosition, mTotalCount);
+    }
+    // Check buffer higher limit
+    else if (start <= lastBufferItem && end > lastBufferItem) {
+        mTotalCount = mTotalCount-(end-lastBufferItem);
+        simpleRemoveItems(lastBufferItem+1, end);
+        mTotalCount = mTotalCount-(lastBufferItem-start+1);
+        simpleRemoveItems(start, lastBufferItem);
+        // Order does matter
+        mTotalCount = mTotalCount-(end-lastBufferItem);
+        simpleRemoveItems(lastBufferItem+1, end);
+        mTotalCount = mTotalCount-(lastBufferItem-start+1);
+        simpleRemoveItems(start, lastBufferItem);
+    }
+    // Check buffer lower limit
+    else if (start < mBufferPosition && end >= mBufferPosition) {
+        // Order does matter
+        mTotalCount = mTotalCount-(end-mBufferPosition+1);
+        simpleRemoveItems(mBufferPosition, end);
+        mTotalCount = mTotalCount-(mBufferPosition-start);
+        simpleRemoveItems(start, mBufferPosition-1);
+    }
+    else {
+        mTotalCount = mTotalCount-removedItemCount;
+        simpleRemoveItems(start, end);
+    }
+}
 
-            // Requested from the end
-            emit requestItems(mBufferPosition+mBufferSize-(last-first+1),
-                              qMin(mBufferPosition+mBufferSize-1, mTotalCount));
-        }
+void HgScrollBufferManager::moveItems(int start, int end, int target)
+{
+    int lastBufferItem = mBufferPosition+mBufferSize-1;
+
+    INFO("Move" << start << "-" << end << "to" << target << ",buffer:" << mBufferPosition << "-" << lastBufferItem << "total count:" << mTotalCount);
+
+    if (mTotalCount < mBufferSize) {
+        // Do nothing
+    }
+    else if (start < mBufferPosition && end > lastBufferItem) {
+        resetBuffer(mBufferPosition, mTotalCount);
+    }
+    else if (start > lastBufferItem && target > lastBufferItem) {
+        // Do nothing
+    }
+    else if (start > lastBufferItem && target < mBufferPosition) {
+        simpleAddItems(start, end);
+    }
+    else if (end < mBufferPosition && target < mBufferPosition) {
+        // Do nothing
+    }
+    else if (end < mBufferPosition && target > lastBufferItem) {
+        simpleRemoveItems(start, end);
+    }
+    else if (start >= mBufferPosition && end <= lastBufferItem &&
+             target >= mBufferPosition && target <= lastBufferItem) {
+        // Do nothing
+    }
+    else {
+        // Rare and complicated use cases: reset the whole buffer
+        resetBuffer(mBufferPosition, mTotalCount);
     }
 }
 
-void HgScrollBufferManager::addItems(int start, int end, int totalCount)
+void HgScrollBufferManager::flushRequestBuffers()
 {
-    int oldTotalCount = mTotalCount;
-    mTotalCount = totalCount;
+    FUNC_LOG;
+
+    qSort(mReleaseBuffer);
+    int releaseCount = mReleaseBuffer.count();
+    int lastReleased = -1;
+    for (int i = 0; i < releaseCount; i++) {
+        UpdatePair update = mReleaseBuffer.at(i);
+        emit releaseItems(qMax(lastReleased+1, update.start()), update.end());
+        lastReleased = update.end();
+    }
+    mReleaseBuffer.clear();
 
-    if (isInsideBuffer(start, end)) {
-        int first = start;
-        int last = end;
+    qSort(mRequestBuffer);
+    int requestCount = mRequestBuffer.count();
+    int lastRequested = -1;
+    for (int i = 0; i < requestCount; i++) {
+        UpdatePair update = mRequestBuffer.at(i);
+        emit requestItems(qMax(lastRequested+1, update.start()), update.end());
+        lastRequested = update.end();
+    }
+    mRequestBuffer.clear();
+}
+
+int HgScrollBufferManager::changeBufferPosition(int newPos)
+{
+    FUNC_LOG;
+    INFO("Change buffer position to" << newPos << "total count:" << mTotalCount);
+    HANDLE_ERROR_BOOL((newPos >= 0));
+    HANDLE_ERROR_BOOL((newPos+mBufferSize <= mTotalCount));
+
+    int bufferShift = newPos-mBufferPosition;
+    if (bufferShift > 0) {
+        mRequestBuffer.shiftRight(mBufferPosition, bufferShift);
+        mReleaseBuffer.shiftRight(mBufferPosition, bufferShift);
+    }
+    else if (bufferShift < 0) {
+        mRequestBuffer.shiftLeft(mBufferPosition, -bufferShift);
+        mReleaseBuffer.shiftLeft(mBufferPosition, -bufferShift);
+    }
+    mBufferPosition = newPos;
+    return bufferShift;
+}
 
-        if (mTotalCount > mBufferSize && mBufferPosition+mBufferSize == oldTotalCount) {
-            // We are at the end of items, keep it that way
-            int oldBufferPos = mBufferPosition;
-            mBufferPosition = qMin(mBufferPosition+(end-start+1), totalCount-mBufferSize);
+/**
+    This function manages only simple item additions: all items are either
+    outside the buffer or inside it.
+    Firs call prepare, then update model, then call fecth.
+*/
+void HgScrollBufferManager::simpleAddItems(int start, int end)
+{
+    FUNC_LOG;
+
+    int lastBufferItem = mBufferPosition+mBufferSize-1;
+    int numAddedItems = end-start+1; // [start, end] inclusive
 
-            if (oldBufferPos < mBufferPosition) {
-                // Release from the beginning
-                emit releaseItems(oldBufferPos, mBufferPosition-1);
-            }
+    if (mTotalCount < mBufferSize) {
+        appendRequestBuffer(start, numAddedItems);
+    }
+    else if (start > lastBufferItem) {
+        // Do nothing
+    }
+    else if (start <= mBufferPosition) {
+        changeBufferPosition(mBufferPosition+numAddedItems);
+        // No need to fetch items, the indexes just change
+    }
+    else {
+        // free from end
+        appendReleaseBuffer(lastBufferItem+1-numAddedItems, numAddedItems);
+        mReleaseBuffer.shiftRight(start, numAddedItems);
+        mRequestBuffer.shiftRight(start, numAddedItems);
+        appendRequestBuffer(start, numAddedItems);
+    }
+}
 
-            // Added items may fall outside the buffer as the buffer is moved
-            if (isInsideBuffer(start, end)) {
-                first = qBound(mBufferPosition, start, mBufferPosition+mBufferSize-1);
-                last = qBound(mBufferPosition, end, mBufferPosition+mBufferSize-1);
-                emit requestItems(first, last);
-            }
+/**
+    This function manages only simple item removals: all items are either
+    outside the buffer or inside it.
+    Firs call prepare, then update model, then call fecth.
+*/
+void HgScrollBufferManager::simpleRemoveItems(int start, int end)
+{
+    FUNC_LOG;
+
+    int lastBufferItem = mBufferPosition+mBufferSize-1;
+    int numRemovedItems = end-start+1; // [start, end] inclusive
+
+    if (start > lastBufferItem) {
+        // Do nothing
+    }
+    else if (end < mBufferPosition) {
+        changeBufferPosition(qMax(0, mBufferPosition-numRemovedItems));
+        // No need to fetch items, the indexes just change
+    }
+    else {
+        if (mTotalCount < mBufferPosition+mBufferSize) {
+            // Buffer is at the end of items
+            int bufferShift = changeBufferPosition(qMax(0, mTotalCount-mBufferSize));
+            // Fetch from beginning
+            // Releasing removed items has been done outside this class
+            appendRequestBuffer(mBufferPosition, qAbs(bufferShift));
         }
         else {
-            first = qBound(mBufferPosition, start, mBufferPosition+mBufferSize-1);
-            last = qBound(mBufferPosition, end, mBufferPosition+mBufferSize-1);
-
-            if (mTotalCount > mBufferSize) {
-                // Release from the end
-                emit releaseItems(mBufferPosition+mBufferSize,
-                                  mBufferPosition+mBufferSize+(last-first+1)-1);
-            }
-            // If all the items fit in the buffer no need to release items
-
-            emit requestItems(first, last);
+            // Fetch from end
+            appendRequestBuffer(lastBufferItem+1-numRemovedItems, numRemovedItems);
         }
     }
 }
 
-void HgScrollBufferManager::moveItems(int start, int end, int target, int totalCount)
+void HgScrollBufferManager::appendRequestBuffer(int start, int count)
+{
+    FUNC_LOG;
+    INFO("Request items" << start << ":" << count)
+
+    mRequestBuffer.add(start, count);
+    mReleaseBuffer.remove(start, count);
+}
+
+void HgScrollBufferManager::appendReleaseBuffer(int start, int count)
+{
+    FUNC_LOG;
+    INFO("Release items" << start << ":" << count)
+
+    mReleaseBuffer.add(start, count);
+    mRequestBuffer.remove(start, count);
+}
+
+UpdatePair::UpdatePair(int start, int count) : mStart(start), mCount(count)
 {
-    if (isInsideBuffer(start) && isInsideBuffer(end) && isInsideBuffer(target)) {
-        return;
-    }
+    HANDLE_ERROR_BOOL(mCount > 0);
+}
+
+int UpdatePair::start() const
+{
+    return mStart;
+}
+
+int UpdatePair::end() const
+{
+    return mStart+mCount-1;
+}
 
-    if (!isInsideBuffer(start, end) && !isInsideBuffer(target)) {
-        return;
-    }
+bool UpdatePair::adjacent(int start, int count) const
+{
+    if (start+count < mStart) return false;
+    if (start > mStart+mCount) return false;
+    return true;
+}
+
+bool UpdatePair::contains(const UpdatePair &other) const
+{
+    if (other.mStart+other.mCount-1 < mStart) return false;
+    if (other.mStart > mStart+mCount-1) return false;
+    return true;
+}
 
-    if (!isInsideBuffer(target)) {
-        if (isInsideBuffer(start) && isInsideBuffer(end)) {
-            if (mBufferPosition+mBufferSize == mTotalCount) {
-                // Fetch from beginning
-                emit requestItems(mBufferPosition, mBufferPosition+end-start);
-            }
-            else {
-                // Fetch from end
-                emit requestItems(mBufferPosition+mBufferSize-(end-start+1),
-                                  qMin(mBufferPosition+mBufferSize-1, mTotalCount));
-            }
+void UpdatePair::extend(int start, int count)
+{
+    int end = qMax(mStart+mCount, start+count);
+    mStart = qMin(mStart, start);
+    mCount = end-mStart;
+    INFO("Pair extended to:" << mStart << ":" << mCount);
+}
+
+void UpdatePair::subtract(int start, int count)
+{
+    int end = qMin(mStart+mCount, start+count);
+    mStart = qMax(mStart, start);
+    mCount = end-mStart;
+    INFO("Pair reduced to:" << mStart << ":" << mCount);
+}
+
+void UpdatePair::shiftRight(int count)
+{
+    mStart += count;
+    INFO("Pair shifted to:" << mStart << ":" << mCount);
+}
+
+void UpdatePair::shiftLeft(int count)
+{
+    mStart -= count;
+    HANDLE_ERROR_BOOL((mStart >= 0));
+    INFO("Pair shifted to:" << mStart << ":" << mCount);
+}
+
+bool UpdatePair::operator== (const UpdatePair &other) const
+{
+    return mStart == other.mStart && mCount == other.mCount;
+}
+
+bool UpdatePair::operator< (const UpdatePair &other) const
+{
+    return (mStart < other.mStart || mStart == other.mStart && mCount < other.mCount);
+}
+
+UpdateBuffer::UpdateBuffer()
+{
+    FUNC_LOG;
+}
+
+void UpdateBuffer::add(int start, int count)
+{
+    FUNC_LOG;
+
+    int itemCount = this->count();
+    for (int i = 0; i < itemCount; i++) {
+        if (at(i).contains(UpdatePair(start, count))) {
+            // It is already there
+            return;
         }
-        else if (isInsideBuffer(start) && end >= mBufferPosition+mBufferSize-1) {
-            emit requestItems(start, mBufferPosition+mBufferSize-1);
-        }
-        else if (start <= mBufferPosition && isInsideBuffer(end)) {
-            emit requestItems(mBufferPosition, end);
-        }
-        else {
-            emit requestItems(mBufferPosition, mBufferPosition+mBufferSize-1);
+        if (at(i).adjacent(start, count)) {
+            (*this)[i].extend(start, count);
+            return;
         }
     }
+    append(UpdatePair(start, count));
+}
 
-    if (isInsideBuffer(target)) {
-        // start-end may be partially inside buffer
-        if (!isInsideBuffer(start, end)) {
-            addItems(target, target+end-start, totalCount);
+void UpdateBuffer::remove(int start, int count)
+{
+    FUNC_LOG;
+
+    int itemCount = this->count();
+    for (int i = itemCount-1; i >= 0; i--) {
+        UpdatePair pair = at(i);
+        UpdatePair comp = UpdatePair(start, count);
+        if (comp.contains(pair)) {
+            INFO("Removing pair" << pair.start() << "-" << pair.end());
+            removeAt(i);
         }
-        else if (isInsideBuffer(start)) {
-            addItems(target+(mBufferPosition+mBufferSize-start), target+end-start, totalCount);
+        else if (pair.contains(comp)) {
+            // Subtraction from middle is not applicable in mediawall use cases
+            (*this)[i].subtract(start, count);
         }
-        else { // end is inside buffer
-            addItems(target, target+mBufferPosition-start-1, totalCount);
+        // Item may be present in multiple pairs.
+    }
+}
+
+void UpdateBuffer::shiftRight(int startingFrom, int amount)
+{
+    FUNC_LOG;
+
+    int itemCount = this->count();
+    for (int i = 0; i < itemCount; i++) {
+        if (at(i).start() >= startingFrom) {
+            (*this)[i].shiftRight(amount);
         }
     }
 }
 
-bool HgScrollBufferManager::isInsideBuffer(int pos)
+void UpdateBuffer::shiftLeft(int startingFrom, int amount)
 {
-    return (pos >= mBufferPosition && pos < mBufferPosition+mBufferSize);
-}
-
-bool HgScrollBufferManager::isInsideBuffer(int start, int end)
-{
-    INFO("Buffer:" << mBufferPosition << "-" << mBufferPosition+mBufferSize-1);
-    INFO("Change:" << start << "-" << end);
+    FUNC_LOG;
 
-    if (isInsideBuffer(start)) {
-        return true;
-    }
-    if (isInsideBuffer(end)) {
-        return true;
+    int itemCount = this->count();
+    for (int i = 0; i < itemCount; i++) {
+        if (at(i).start() >= startingFrom) {
+            (*this)[i].shiftLeft(amount);
+        }
     }
-    if (start < mBufferPosition && end >= mBufferPosition+mBufferSize) {
-        return true;
-    }
-
-    INFO("Buffer not affected");
-    return false;
 }
-