Source Code 2018 Foot-Yaw Resolver

// if so, move yaw = move yaw ideal, and we can calculate foot yaw by an accuracy of ~45 degrees
if( started_moving_this_frame && previous_record->layers[ 6 ].weight <= 0.f && !record->in_air( ) )
{
    const float local_cycle_increment = record->layers[ 6 ].playback_rate;
    float raw_yaw_ideal = atan2( -record->anim_velocity.y, -record->anim_velocity.x ) * 180.f /
        constants::pi;
    if( raw_yaw_ideal < 0.f )
        raw_yaw_ideal += 360.f;

    const int move_seq = record->layers[ 6 ].sequence;
    float move_yaw = FLT_MAX;
    constexpr std::array angles = { 180.f, 135.f, 90.f, 45.f, 0.f, -45.f, -90.f, -135.f };
    for( int i = animtag_startcycle_n; i <= animtag_startcycle_nw; i++ )
    {
        const float pred_cycle = player->animation_state( )->clamp_cycle(
            player->first_sequence_anim_tag( move_seq, i ) + local_cycle_increment );
        if( static_cast< int >( pred_cycle * 1000.f ) == static_cast< int >( record->layers[
            animation_layer_movement_move ].cycle * 1000.f ) )
        {
            move_yaw = angles[ i - animtag_startcycle_n ];
            break;
        }
    }

    if( move_yaw != FLT_MAX )
    {
        const float foot_yaw = g_math.angle_normalize( g_math.angle_diff( raw_yaw_ideal, move_yaw ) );
    }
}