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This is the lowest level entry to the engine. It also maps quite conveniently to Quake-C stuff, so check that out! This is not an exhaustive list, but I'll hopefully be adding to it as I find out more, and people send me in info (hint hint). How engine functions work Engine functions are passed by Half-Life to the dll. Pointers to these functions can be found in g_engfuncs. They are listed in eiface.h. Valve have nicely provided us with easy-to-use wrappers for these functions (e.g. VEC_TO_ANGLES. They can be found in enginecallback.h. Engine Functions g_engfuncs.pfnSetClientMaxspeed void pfnSetClientMaxspeed(const edict_t *pEdict, float fNewMaxspeed); Pass this function an edict to a client (eg a player) and a max speed, and you've just forced his maximum movement speed. This is used in TFC to slow down flag holders or heavy-weapons players. g_engfuncs.pfnChangeYaw void pfnChangeYaw(edict_t* ent); void oldCHANGE_YAW(edict_t* ent); This function should be called every 0.1 seconds. It causes the given entity to turn towards its pev->ideal_yaw at a speed specified by pev->yaw_speed. ideal_yaw is measured in 'world' angles and yaw_speed is measured in degrees per second (as long as the function is called every 0.1 seconds.) See the challenge 1 solution for a description of how to use this. g_engfuncs.pfnChangePitch void pfnChangePitch(edict_t* ent); void CHANGE_PITCH(edict_t* ent); UNTESTED This probably performs the same function as pfnChangeYaw, except that it affects the pitch rather than the yaw. g_engfuncs.pfnWalkMove int pfnWalkMove(edict_t* ent, float yaw, float dist, int iMode); int WALK_MOVE(edict_t* ent, float yaw, float dist, int iMode); This function is used to make an entity move around as if it is walking. This means that the engine performs the necessary calculations to make the entity go up slopes and steps. The movetype of the entity should be MOVETYPE_STEP. iMode can be one of the following: WALKMOVE_NORMAL WALKMOVE_WORLDONLY (doesn't hit any entities) WALKMOVE_CHECKONLY (doesn't touch triggers) ent is the entity to move, yaw is the direction in which to move it and dist is the distance to move it. Sequences define their linear movement values, and this can be obtained by using the SDK function GetSequenceInfo. An easier way is to call ResetSequenceInfo which will automatically set the member variable m_flGroundSpeed to be ten times the value to pass in to WALK_MOVE. See the challenge 2 solution for an example of this function.