Cdtrjyty

ToME 4 uses both turns and action speed in its terminology, and it's confusing me.

Is one turn a set amount of game time (e.g. 2.6 seconds), an abstract "as long as it takes one to act" kind of deal, or something else entirely? This is extremely important, because it heavily affects how I should interact with timed effects.

For example, if I get a buff that lasts 10 turns, will increasing my action speed burn through the effect faster (because I take my 10 actions sooner), or get me more its use (because I can take more actions over the effect's fixed duration)?

Essentially, a turn is "however long your action takes". In particular, it is independent of real time - you can let the game sit as long as you want, and it will wait for you. More precisely (after skimming the source code), various actions take different amounts of energy. The actors, including your character, gain some energy (how much depends on factors such as their speed) on each internal tick. When you have accumulated enough energy to do something, the game pauses (i.e. no more ticks) until you have acted.

You're on the right track: each action takes a fixed amount of time. In the very basic sense they are 0 (instant) or 1 turn.

Then you get into modifiers. Say your movement speed is 120% of normal and a creature is at 100%. You'll move 12 tiles for every 10 that he moves, meaning you can eventually outrun him.

To your latter example, you get more actions per turn. It's very noticeable with a Movement infusion (where you might get 400 or 500% movement speed). Watch the monsters as you run away.

Global speed works the same way but also applies to attacking, casting and all other actions you might take, and stacks up with movement speed.

First, see the wiki page for Character sheet, in the Speed section: Speed determines how many 'actions' you can do in a turn. At 100% global speed you can do one action, at 200% global speed you can do two actions, and so on. Global speed is modified by the additive movement/spell/attack/mental speeds. So if your character has a global speed of 200%, a movement speed of 0%, and an attack speed of -100%, then each movement takes half a turn, while each attack takes a full turn.

Second, see the page for Speed. To determine when Actors get to take an action, the game gives them 1000 energy points per turn (EPT). A regular attack costs 1000 energy points per hit (EPH). So an actor with a 100% global speed, and no attack speed or weapon speed modifiers will spend all of their energy in one attack. Increasing global speed increases the amount of energy you get per turn, e.g., 140% global speed means you get 1400 EPT. Increasing weapon speed or attack speed reduces EPH: EPH = 1000 / ((1 + attack speed) * weapon speed). For example, a 110% sword wielded by a character with -30% attack speed will have EPH = 1000 / (0.7 * 1.1) = 1000 / 0.77 = 1299. If that character has a global speed of 140%, they would get 1400 EPT. After spending 1299 on an attack, they would be left with 101 energy. Next turn they would get another 1400 energy, attack, and be left with 202...after 14 turns they store up enough energy for two attacks in one turn.

So if you have a buff that lasts X turns, increasing your speed sufficiently will let you get more actions before the buff ends.

To see the turns/energy in the source code, in the current version (1.5.10) look at GameEnergyBased.lua. Line 95 defines tickLevel, which loops through an array of entities on the level, gives each entity "energy_per_tick" (aka EPT), and then calls the entity's act function (i.e., asks for an action) at line 129.