make start positions per-device

Author: aalkin

Framework/Core/include/Framework/DeviceControl.h

@@ -52,6 +52,8 @@ struct DeviceControl {
   int logStreams = 0;
   /// An incremental number to identify the device state
   int requestedState = 0;
+  /// The first slot in the records buffer to display in GUI
+  int firstSlot = 0;
 };
 
 } // namespace o2::framework

Framework/GUISupport/src/FrameworkGUIDevicesGraph.cxx

@@ -725,9 +725,9 @@ void showTopologyNodeGraph(WorkspaceGUIState& state,
     }();
     if (records > 0) {
       ImGui::PushItemWidth(140);
-      ImGui::SliderInt("##window", &v, 0, records - gui::WND, "start: %d", ImGuiSliderFlags_AlwaysClamp);
+      ImGui::SliderInt("##window", &controls[node->ID].firstSlot, 0, records - gui::WND, "start: %d", ImGuiSliderFlags_AlwaysClamp);
     }
-    gui::displayDataRelayer(metricsInfos[node->ID], infos[node->ID], specs[node->ID], allStates[node->ID], ImVec2(140., 90.), v);
+    gui::displayDataRelayer(metricsInfos[node->ID], infos[node->ID], specs[node->ID], allStates[node->ID], ImVec2(140., 90.), controls[node->ID].firstSlot);
     ImGui::EndGroup();
 
     // Save the size of what we have emitted and whether any of the widgets are being used