INTERNALS.md

Internals

These may get out of date.

Reverse Engineering

I use NSA's Ghidra to analyse the following files:

• steam/steamapps/common/Team Fortress 2 Dedicated Server/tf/bin/server_srv.so
• steam/steamapps/common/Team Fortress 2 Dedicated Server/tf/bin/server.dll

The process requires some knowledge of C and C++.

The auto-analysis will take in the range of half an hour to a couple hours. If it results in lots of errors on Ghidra 9.1.2, try downgrading to 9.1 temporarily.

The Linux binary (server_srv.so) is unstripped, which means it contains the symbols unmodified. This is particularly helpful to research and prototype. The Windows binary does not contain any debugging information.

DepotDownloader can be used to download previous versions of the binaries alongside steamdb.info.

Leaks

Some leak of the source code before Jungle Inferno can easily be found online, the search term hl2_src should give you succesful results.

Remove Medic Attach Speed

The method CTFPlayer::TeamFortress_CalculateMaxSpeed(this, bool) contains the behavior we are trying to change, consider the following pseudocode:

float CTFPlayer::TeamFortress_CalculateMaxSpeed(CTFPlayer *this, param) {
    // ..

    float max_speed = 0.0;
    auto active_weapon = CBaseCombatCharacter::GetActiveWeapon(this);

    // ..

    if (this->class == Medic) {
        max_speed = MEDIC_MAX_SPEED;

        if (active_weapon != NULL
                && (medigun = dynamic_cast<CTFWeaponMedigun *>(active_weapon) )
                && medigun != NULL
                && medigun->target_id != INVALID_TARGET) {

            auto medigun_type = CWeaponMedigun::GetMedigunType(medigun);
            auto medigun_target = g_players[medigun->target_id];

            if (medigun_type == 2 // Quick-Fix
                    && CTFPlayerShared::InCond(medigun_target, COND_SHIELD_CHARGING)) {
                max_speed = g_tf_max_charge_speed;
            } else {
                float medigun_target_speed =
                    CTFPlayer::TeamFortress_CalculateMaxSpeed(medigun_target, true),

                // -- WE DON'T WANT THIS
                if (medigun_target_speed > max_speed) {
                    max_speed = medigun_target_speed;
                }
                // -- WE DON'T WANT THIS
            }
        }
    }

    // ..

    return max_speed;
}

In this, we see that CTFPlayer::TeamFortress_CalculateMaxSpeed is called to get the speed of the medigun target. The boolean parameter is set to true, and that is the only occurence in the binary. This parameter probably exists to ignore the max speed achieved when a demoman is charging with a shield, and instead fetches the max speed while not charging.

We can easily patch this behavior by hooking CTFPlayer::TeamFortress_CalculateMaxSpeed itself and returning 0.0 when this parameter is set to true. Obviously, this applies to all mediguns, the Quick-Fix included. The Quick-Fix still benefits from the speed boost while a demoman is charging.

Fix Ghost Crossbow Bolts & Projectiles Ignore Teammates

The virtual method bool CBaseProjectile::CanCollideWithTeammates(*this) returns the field m_bCanCollideWithTeammates which is initialized to false and updated to true during CollideWithTeammatesThink. CBaseProjectile::Spawn() schedules this Think to execute after gpGlobals->curtime + GetCollideWithTeammatesDelay(), the latter returning 250ms by default. The file concerned is game/shared/baseprojectile.cpp.

CTFProjectile_HealingBolt overrides GetCollideWithTeammatesDelay to always return 0ms, however the projectile obviously doesn't collide with teammates as soon as it spawns. I believe this behavior to not be expected, the intent seems to want it collide as soon as possible but it seems that Thinks are only precise over a few server ticks.

One could argue that developers were aware of the effects of both methods as CTFProjectile_GrapplingHook, which is just below and shares its mother class with CTFProjectile_HealingBolt, and simply overrides CanCollideWithTeammates to always return false. I don't believe this to be a fair assessment. Grappling hooks were added later on, and the only way to implement the logic to ignore teammates would have been by overriding CanCollideWithTeammates (or CollideWithTeammatesThink), possibly creating the need for a virtual method altogether. In this case, as the behaviors are different and as the Crossbow's current implementation was probably not known to be an issue, it was overlooked and was not updated. The file concerned is game/server/tf/tf_projectile_arrow.cpp.

On entity creation, we can simply hook this virtual method to always return true when the classname is tf_projectile_healing_bolt, or otherwise false if it starts with tf_projectile_.