Bit Count

The bit count of Integer based fields can be set using the BitCountAttribute.

This will truncate the bits so that only the small bits are sent. There is no range checking for values using BitCount, so the value that is too big or negative will not be unpacked correctly

This means that BitCount should not be used with values that can be negative because this data will be lost. If you do need to send negative values then use ZigZagEncode or BitCountFromRange

Use cases

• A Value with a maximum value
• An index in an array of known size
  • eg array with 10 elements, the index can be sent as 4 bits
• A Random int hash where you only need to send 16 bits

Supported Types

• Byte
• Short
• UShort
• Int
• Uint
• Long
• ULong
• Enum

Example 1

Health which is between 0 and 100

public class MyNetworkBehaviour : NetworkBehaviour 
{
    [SyncVar, BitCount(7)]
    public int Health;
}

BitCount = 7 so max value of Health is 127

health = 57 will serialize to 011_1001

health = -1 (out of range) will serialize to 111_1111

health = 130 (out of range) will serialize to 000_0010

Example 2

Weapon index in a list of 6 weapons

public class MyNetworkBehaviour : NetworkBehaviour 
{
    [SyncVar, BitCount(3)]
    public int WeaponIndex;
}

BitCount = 3 so max value of Health is 7

WeaponIndex = 5 will serialize to 101

Generated Code

Source:

[SyncVar, BitCount(7)]
public int myValue;

Generated:

public override bool SerializeSyncVars(NetworkWriter writer, bool initialState)
{
    ulong syncVarDirtyBits = base.SyncVarDirtyBits;
    bool result = base.SerializeSyncVars(writer, initialize);

    if (initialState) 
    {
        writer.Write((ulong)this.myValue, 7);
        return true;
    }

    writer.Write(syncVarDirtyBits, 1);
    if ((syncVarDirtyBits & 1UL) != 0UL)
    {
        writer.Write((ulong)this.myValue, 7);
        result = true;
    }

    return result;
}

public override void DeserializeSyncVars(NetworkReader reader, bool initialState)
{
    base.DeserializeSyncVars(reader, initialState);

    if (initialState)
    {
        this.myValue = reader.Read(7);
        return;
    }

    ulong dirtyMask = reader.Read(1);
    if ((dirtyMask & 1UL) != 0UL)
    {
        this.myValue = reader.Read(7);
    }
}

Last updated for Mirage v101.8.0.