fixed linux compilation issues

app/widget/slider/floatslider.cpp

@@ -20,6 +20,7 @@
 
 #include "floatslider.h"
 
+#include <cmath>
 #include <QAudio>
 #include <QDebug>
 

app/widget/timelinewidget/timelineundo.h

@@ -1356,12 +1356,13 @@ private:
 class TimelineAddTrackCommand : public UndoCommand {
 public:
   TimelineAddTrackCommand(TrackList *timeline) :
-    timeline_(timeline)
+    timeline_(timeline),
+    direct_(nullptr)
   {
     track_ = new Track();
     track_->setParent(&memory_manager_);
 
-    if (Config::Current()[QStringLiteral("AutoMergeTracks")].toBool()) {
+    if (timeline->GetTrackCount() > 0 && Config::Current()[QStringLiteral("AutoMergeTracks")].toBool()) {
       if (timeline_->type() == Track::kVideo) {
         MergeNode* merge = new MergeNode();
         base_ = merge->base_in();
@@ -1379,6 +1380,11 @@ public:
     }
   }
 
+  Track* track() const
+  {
+    return track_;
+  }
+
   virtual Project* GetRelevantProject() const override
   {
     return timeline_->GetParentGraph()->project();
@@ -1409,6 +1415,21 @@ public:
       // Connect this as the "blend" track
       Node::ConnectEdge(track_, blend_);
       Node::ConnectEdge(last_track, base_);
+    } else if (timeline_->GetTrackCount() == 1) {
+      // If this was the first track we added,
+      NodeInput* relevant_input;
+
+      if (timeline_->type() == Track::kVideo) {
+        relevant_input = timeline_->parent()->texture_input();
+      } else {
+        relevant_input = timeline_->parent()->samples_input();
+      }
+
+      if (!relevant_input->IsConnected()) {
+        Node::ConnectEdge(track_, relevant_input);
+
+        direct_ = relevant_input;
+      }
     }
   }
 
@@ -1429,6 +1450,8 @@ public:
       }
 
       merge_->setParent(&memory_manager_);
+    } else if (direct_) {
+      Node::DisconnectEdge(track_, direct_);
     }
 
     // Remove track
@@ -1445,6 +1468,8 @@ private:
   NodeInput* base_;
   NodeInput* blend_;
 
+  NodeInput* direct_;
+
   QObject memory_manager_;
 
 };