Code Generation

To synchronize variables, Mirage uses property-based [SyncVar] definitions. During the build process, the Weaver intercepts each auto-property, completely clearing its compiled getter and setter method bodies. It then injects custom IL directly into these accessors:

• Getter: Directly returns the backing field (e.g. ldfld).
• Setter: Injects an equality check (SyncVarEqual), a dirty flag update (SetDirtyBit), hook execution checks, and updates the backing field.

The compiler also generates SerializeSyncVars and DeserializeSyncVars methods to serialize/deserialize these values.

So for this script:

public class Data : NetworkBehaviour
 {
     [SyncVar(hook = nameof(OnInt1Changed))]
     public int int1 = 66;

     [SyncVar]
     public int int2 = 23487;

     [SyncVar]
     public string MyString = "Example string";

     void OnInt1Changed(int oldValue, int newValue)
     {
         // do something here
     }
 }

The following sample shows the code that is generated by Mirage for the SerializeSyncVars function which is called inside NetworkBehaviour.OnSerialize:

public override bool SerializeSyncVars(NetworkWriter writer, bool initialState)
 {
     // Write any SyncVars in base class
     bool written = base.SerializeSyncVars(writer, initialState);

     if (initialState)
     {
         // The first time a game object is sent to a client, send all the data (and no dirty bits)
         writer.WritePackedUInt32((uint)this.int1);
         writer.WritePackedUInt32((uint)this.int2);
         writer.Write(this.MyString);
         return true;
     }
     else 
     {
         // Writes which SyncVars have changed
         writer.Write(base.SyncVarDirtyBits, 3);

         if ((base.SyncVarDirtyBits & 1uL) != 0uL)
         {
             writer.WritePackedUInt32((uint)this.int1);
             written = true;
         }

         if ((base.SyncVarDirtyBits & 2uL) != 0uL)
         {
             writer.WritePackedUInt32((uint)this.int2);
             written = true;  
         }

         if ((base.SyncVarDirtyBits & 4uL) != 0uL)
         {
             writer.Write(this.MyString);
             written = true;     
         }

         return written;
     }
 }

The following sample shows the code that is generated by Mirage for the DeserializeSyncVars function which is called inside NetworkBehaviour.OnDeserialize:

public override void DeserializeSyncVars(NetworkReader reader, bool initialState)
 {
     // Read any SyncVars in base class
     base.DeserializeSyncVars(reader, initialState);

     if (initialState)
     {
         // The first time a game object is sent to a client, read all the data (and no dirty bits)
         int oldInt1 = this.int1;
         this.int1 = (int)reader.ReadPackedUInt32();
         // if old and new values are not equal, call hook
         if (!base.SyncVarEqual<int>(oldInt1, this.int1))
             this.OnInt1Changed(oldInt1, this.int1);

         this.int2 = (int)reader.ReadPackedUInt32();
         this.MyString = reader.ReadString();
         return;
     }

     ulong dirtySyncVars = reader.Read(3);
     base.SetDeserializeMask(dirtySyncVars, 0);

     // is 1st SyncVar dirty
     if ((dirtySyncVars & 1uL) != 0uL)
     {
         int oldInt1 = this.int1;
         this.int1 = (int)reader.ReadPackedUInt32();
         // if old and new values are not equal, call hook
         if (!base.SyncVarEqual<int>(oldInt1, this.int1))
             this.OnInt1Changed(oldInt1, this.int1);
     }

     // is 2nd SyncVar dirty
     if ((dirtySyncVars & 2uL) != 0uL)
         this.int2 = (int)reader.ReadPackedUInt32();

     // is 3rd SyncVar dirty
     if ((dirtySyncVars & 4uL) != 0uL)
         this.MyString = reader.ReadString();
 }

If a NetworkBehaviour has a base class that also has serialization functions, the base class functions should also be called.