Action-Queue
While in Gothic, every Vob can have an Action-Queue, they are most used by Npcs. Actually, the Action-Queue is the inner core of Npc behavior!
The Action-Queue itself is best described as a First-In-First-Out buffer with extra steps. It holds actions of the following categories:
- Damage
- Weapon
- Movement (Go somewhere)
- Attack (Single attacks)
- UseItem
- Script State
- Manipulate (Items/Mobs)
- Conversation
- Magic
For a full list of categories and sub-types, basically everything an Npc can do in Gothic, see this document.
On every frame, the action at the front of the queue is executed. The action itself can decide whether it is done after it was executed, or if it needs to be executed again next frame:
- If the action says it is done, it will be popped from the queue and the next action will be executed next frame.
- If the action is not done yet, it will stay at the front of the queue and will be executed again next frame.
Example
Let's assume the following sequence of actions has been pushed into an Npcs Action-Queue:
| Index | 0 | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| Action | Goto Location | Take Item | Use Item (Beer) | Goto Character (Player) | Give Item (5x Ore) |
The Action at index 0 (Goto Location) is at the front of the queue and thus will be executed for as long as the Npc is not at the target location.
On every frame, when the Goto Location action is executed, it will check whether the Npc arrived at its destination. Lets say, it did. Then, the action will be popped off the Queue and the next one takes its place. The Queue now looks like this:
| Index | 0 | 1 | 2 | 3 |
|---|---|---|---|---|
| Action | Take Item | Use Item (Beer) | Goto Character (Player) | Give Item (5x Ore) |
The next Action is now at the front of the queue and will be executed. For Take Item, it will block the queue until all animations have been finished and the item is in the inventory (if the Npc could pick it up, that is). After the item was picked up, the Action signals that it is done. The queue now looks like this:
| Index | 0 | 1 | 2 |
|---|---|---|---|
| Action | Use Item (Beer) | Goto Character (Player) | Give Item (5x Ore) |
And so on, you get the Idea.
Filling the Queue via Scripting
The Action-Queue is the most important system to let the games scripts work in the way they do. Many of the Npc related script external functions actually just push an action into the queue and continue with executing the script.
Most commonly used in dialogues, the AI_Output external lets a character say something. In the original scripts, a dialogue can look like this:
FUNC void PC_Thief_WHEEL_Info()
{
AI_Output(self, hero,"PC_Thief_WHEEL_Info_11_01"); //Die Winde scheint zu klemmen.
AI_Output(self, hero,"PC_Thief_WHEEL_Info_11_02"); //Lass mich mal, vielleicht kann ich da was machen!
AI_StopProcessInfos(self); // Cancels dialogue
AI_GotoWP(self,"LOCATION_12_14_WHEEL");
AI_AlignToWP(self);
AI_PlayAni(self,"T_PLUNDER");
};
In this dialogue option, Diego tells the Hero "Let me try" and goes to the
broken wind to turn it. All those AI_-functions push an action into Diegos
Action-Queue and are executed sequentially, one after another.
Overlay Events
Usually, only the event at the front of the queue is active and passed to the target object. However, events marked as "Overlay" will act a little bit different.
If such an overlay-event is at the front of the queue, it will be passed to the target object every update cycle. Then, the next event in the queue is looked at. If that is also an overlay-event, it is passed to the object as well.
This continues until the first event is encountered which is not an overlay. That will be the last event passed to the object.