Fix the remaining compositing issues reported by Harald (mimick the 18.x behavior)

src/timeline2/model/builders/meltBuilder.cpp

@@ -134,31 +134,28 @@ bool constructTimelineFromMelt(const std::shared_ptr<TimelineItemModel> &timelin
     }
     // Sort compositions and insert
     bool compositionOk = true;
-    if (!compositions.isEmpty()) {
-        std::sort(compositions.begin(), compositions.end(), [](Mlt::Transition *a, Mlt::Transition *b) { return a->get_b_track() > b->get_b_track(); });
-        while (!compositions.isEmpty()) {
-            QScopedPointer<Mlt::Transition> t(compositions.takeFirst());
-            auto transProps = std::make_unique<Mlt::Properties>(t->get_properties());
-            QString id(t->get("kdenlive_id"));
-            int compoId;
-            int aTrack = t->get_a_track();
-            if (aTrack > tractor.count()) {
-                m_errorMessage << i18n("Invalid composition %1 found on track %2 at %3, compositing with track %4.", t->get("id"), t->get_b_track(),
+    while (!compositions.isEmpty()) {
+        QScopedPointer<Mlt::Transition> t(compositions.takeFirst());
+        auto transProps = std::make_unique<Mlt::Properties>(t->get_properties());
+        QString id(t->get("kdenlive_id"));
+        int compoId;
+        int aTrack = t->get_a_track();
+        if (aTrack > tractor.count()) {
+            m_errorMessage << i18n("Invalid composition %1 found on track %2 at %3, compositing with track %4.", t->get("id"), t->get_b_track(),
                                        t->get_in(), t->get_a_track());
-                continue;
-            }
+            continue;
+        }
 
-            compositionOk = timeline->requestCompositionInsertion(id, timeline->getTrackIndexFromPosition(t->get_b_track() - 1), t->get_a_track(), t->get_in(),
+        compositionOk = timeline->requestCompositionInsertion(id, timeline->getTrackIndexFromPosition(t->get_b_track() - 1), t->get_a_track(), t->get_in(),
                                                                   t->get_length(), std::move(transProps), compoId, undo, redo);
-            if (!compositionOk) {
-                qDebug() << "ERROR : failed to insert composition in track " << t->get_b_track() << ", position" << t->get_in() << ", ID: " << id
+        if (!compositionOk) {
+            qDebug() << "ERROR : failed to insert composition in track " << t->get_b_track() << ", position" << t->get_in() << ", ID: " << id
                          << ", MLT ID: " << t->get("id");
-                // timeline->requestItemDeletion(compoId, false);
-                m_errorMessage << i18n("Invalid composition %1 found on track %2 at %3.", t->get("id"), t->get_b_track(), t->get_in());
-                continue;
-            }
-            qDebug() << "Inserted composition in track " << t->get_b_track() << ", position" << t->get_in() << "/" << t->get_out();
+            // timeline->requestItemDeletion(compoId, false);
+            m_errorMessage << i18n("Invalid composition %1 found on track %2 at %3.", t->get("id"), t->get_b_track(), t->get_in());
+            continue;
         }
+        qDebug() << "Inserted composition in track " << t->get_b_track() << ", position" << t->get_in() << "/" << t->get_out();
     }
 
     // build internal track compositing

src/timeline2/model/timelinemodel.cpp

@@ -2572,7 +2572,7 @@ bool TimelineModel::requestCompositionMove(int compoId, int trackId, int composi
 
 bool TimelineModel::replantCompositions(int currentCompo, bool updateView)
 {
-    // We ensure that the compositions are planted in a decreasing order of b_track.
+    // We ensure that the compositions are planted in a decreasing order of a_track, and increasing order of b_track.
     // For that, there is no better option than to disconnect every composition and then reinsert everything in the correct order.
     std::vector<std::pair<int, int>> compos;
     for (const auto &compo : m_allCompositions) {
@@ -2588,7 +2588,13 @@ bool TimelineModel::replantCompositions(int currentCompo, bool updateView)
         }
     }
     // sort by decreasing b_track
-    std::sort(compos.begin(), compos.end(), [](const std::pair<int, int> &a, const std::pair<int, int> &b) { return a.first > b.first; });
+    std::sort(compos.begin(), compos.end(), [&](const std::pair<int, int> &a, const std::pair<int, int> &b) { 
+        if (m_allCompositions[a.second]->getATrack() == m_allCompositions[b.second]->getATrack()) {
+            return a.first < b.first;
+        }
+        return m_allCompositions[a.second]->getATrack() > m_allCompositions[b.second]->getATrack();
+        
+    });
     // replant
     QScopedPointer<Mlt::Field> field(m_tractor->field());
     field->lock();