Add support for drawing timeline item overlays.

server/TracyTimelineItem.cpp

@@ -53,6 +53,7 @@ void TimelineItem::Draw( bool firstFrame, double pxns, int& offset, const ImVec2
         }
     }
 
+    DrawOverlay( wpos + ImVec2( 0, oldOffset ), wpos + ImVec2( w, offset ) );
     ImGui::PopClipRect();
 
     float labelWidth;

server/TracyTimelineItem.hpp

@@ -35,6 +35,7 @@ protected:
     virtual int64_t RangeEnd() const = 0;
 
     virtual bool DrawContents( double pxns, int& offset, const ImVec2& wpos, bool hover, float yMin, float yMax ) = 0;
+    virtual void DrawOverlay( const ImVec2& ul, const ImVec2& dr ) {}
 
     virtual bool IsEmpty() const { return false; }