Analyse the call graph to identify potential classes to be factored out of C code.
Create a DGML file using a tool for reading the source code, for example
DeepEnds ReadCpp extract=callgraph output=C:\project\callgraph.dgml C:\project\source.sln
Note that the analyser expects
C++ style structs.
Run the cluster tool, for example,
DeepEnds ReportClusters --output=C:\project\clusters.dgml C:\project\callgraph.dgml
Open the clusters file in the DGML editor of Visual Studio. The clusters that have been extracted will have been placed in numbered groups.
Find a cluster of interest and move it around between groups that it is connected to. Move nodes into that cluster until satisfied with an outline class.
Move the code around to be consistent with the outline class diagram.