This RPC is used to teleport players to a location.

Rpc[21] := xLerped:u16 yLerped:u16 sid:u16;

When a player receives this message and the sequence id (sid) is recent enough, the player is teleported to the specified location.

Usage

There are two scenarios where SnapTo is used: while venting or when spawning in Airship.

If a player moves to another vent, SnapTo is used with the position of the new vent. See EnterVent and ExitVent for more details about the ventilation system.

The second scenario involves the Airship map: this map has a minigame to pick a spawn location at the start of the game and after every meeting. First every player is teleported to -25,40, which is not visible from the rest of the map. Every player then gets three random spawn suggestions out of a pool of 6 items. After picking an location SnapTo is called by the client to the chosen location. The following table lists the 6 possible spawn location and their coordinates.

Lerping

The coordinates sent by this RPC are compressed using linear interpolation between -50 and 50. This has a few advantages:

1. This saves a few bytes: instead of sending a 4-byte float, 2 bytes are sent. As movement packets are the most common packet, this is a worthwhile optimization.
2. Floating point numbers do not have an equal precision across their range. Floating points use an exponent to quickly change to a different scale and can only represent a limited amount of values per exponent. Basically, if you have a very lange number you can't store as much data below the decimal point as you can with a number like 0 or 1. For Among Us this is less of a concern, since its maps are very small, but in larger games this may become problematic.

To convert between a lerped coordinate and an unlerped coordinate, use the following code:

/// Convert a floating point x to a value in the range between min and max
/// In Among Us, min = -50 and max = 50
public ushort Lerp(float min, float max, float x)
{
    // Clamp your value of x to inside your range
    if (x <= min) {
        return 0;
    }
    if (x >= max) {
        return 65535;
    }
    // Calculate the total range of your linear interpolation
    float range = max - min;
    // Subtract the minimum from x turns x into a value between 0 and range.
    // Divide by your source range turns x into a value between 0 and 1
    // Finally multiply by your target range (in this case, all 16 bit unsigned integers, so between 0 and 65535)
    float f = (x - min) / range * 65535f;
    return (ushort) f;
}

/// Convert an unsigned 16-bit integer x to a value between min and max
public float Unlerp(float min, float max, ushort x)
{
    // Calculate the total range of your linear interpolation
    float range = max - min;
    // First cast x to an floating point otherwise all following calculations aren't precise.
    // Dividing by 65535 turns x into a value between 0 and 1
    // Multiplying by range turns x into a value between 0 and range
    // Then add min to turn x into a value between min and max
    return ((float) x) / 65535f * range + min;
}

Sequence ID

All movement updates in Among Us have a sequence id: this allows packets to get reordered without consequences. Movement packets with a lower sequence ID are ignored. To make sure that the SnapTo RPC is processed, the sequence ID counter is incremented by 5 when SnapTo is sent.

Version History