Goal oriented gameplay (was: generators, triggers and aiming)

[Eero Tamminen]

Hi,

Here's the new TODO list with updated generator, trigger and aim syntax.

TODO (goal oriented game play)
====

* Get old features back to the biplane:
  - Disable plane controlling once it's gotten too much damage
  - Kill plane after a while after it's gotten enough damage

* Make everything in Airstrike an object: ai, trigger, generator etc.

* Add types to objects:
  - Member for the object type
  - Parent link that points to parent object type
  - Helper function that traverses the type tree to root and checks
    whether object or it's parent type had requested type
  - Cast macros for the base types: sprite|mech|trigger|generator|ai|aim
    using the helper/traverse function. If cast macros are compiled
    without debug, they do just casting, not the check
  - Everywhere objects are cast, these macros are used

* Note: Sprite capabilities and attribute checks are handled with
  messages (e.g. MSG_IS_WALKING). This is needed by triggers

* Add to object type struct counters for how many objects (sprites) of the
  given type have been created and killed (live = created - killed).
  - Modify these counters when objects are created/killed
  - Add clearing of these stats to and call that on level load or unload.

* Add generator objects:
  - generator <name tag> <sprite type> <x> <y> <generator type> [options]

  When this gets activate message, it creates a sprite of the given
  type to the x,y co-ordinates.  Same generator can get messages
  from multiple triggers.

  Available generator types and their (additional) options would be:
  - player <index> <count> [tag]
    - Assigns an AI given from Airstrike command line to the sprites:
    	airstrike -level <nr> <ai-1> <ai-2> <ai-3> <etc>
    - If 'tag' is set, tags the sprite (needed e.g. for aiming)
    - Monitors the sprite and creates a new when old dies <count> times
      - Whe activated, sets player# as alive on the level
      - When count has finished, sets player# as dead for the level,
        see "playerdead" and "playeralive" triggers
      - With count some levels or players can have less lives
  - singleton <count>
    - Creates a new sprite once the old one has been killed, but does it
      only for a certain number of times. This can be done by checking
      the object type live count (= created - freed objects), it doesn't
      need to ref the object
  - random <rx> <ry>
    - The creation happens at given random positive/negative offset
  - ai <ai>
    - Sprites are generated with given AI

* Add triggers:
  - trigger <name tag> <object tag1,tag2...> <event type> [options]
  Sends activate message to the all given tagged objects when an event
  of the given type happens.  Used to trigger generators, aims and other
  triggers, or even individual tagged objects.

  Object tag "level-done" is a special one for setting LEVEL_DONE flag
  and tag "level-fail" for setting LEVEL_FAIL flag.  "level-winner" tag
  is for setting the level "winner" member to the AI of the sprite that
  completed the level (triggered level-end condition).
  
  Available event types and their options would be:
  - playerdead <count>
    - Activation happens when at least <count> players have been killed
      (until they are dead)
  - playeralive <count>
    - Activation happens when only <count> players are alive
  - timer <ms> [count]
    - Activation happens after each <ms> millisecs period until count 
reached
  - random <min ms> <max ms> [count]
    - Activation happens at random time interval until count reached
  - spritekill <sprite type> <min kill count>
  - spritecreate <sprite type> <min create count>
    - Whether player (or other objects) have created/killed
      enough of these types of objects
  - spriteactive <sprite type> <min count> <max count>
    - Triggered if number of live (created-freed) sprites of given type
      get into given range (or would out of range be better?)
  - proximity <x> <y> <r> [above|below|left|right]
    - If one of above|below|left|right is set, proximity is checked
      only in that direction
    - Sends MSG_SET_TARGET message for the found sprite to the tagged object
      (not activate message)
    - Needs to scan through all live sprites :-/
  - aicontrol <ai> <tag>
    - Used to check whether <ai> has gained control of a tagged object
    - Basically checks which AI the tagged object has
  - tagkill <tag>
    - Used to check whether anything has killed tagged object

* Implement global aim for objects and shell syntax:
   - aim <name tag> <sprite type> <tag> [ai]
   When this gets activate message, it makes sprites of given type to
   follow the object with given tag. If 'ai' is set, objects should
   use that instead of the default following AI.  Tag "NONE" can be
   used (later) to clear the tag from aiming.
   
   This might be done e.g. by having the aim as additional information
   in the sprite type structs:
   struct {
      sprite_type_t type;	/* current sprite type stuff */
      int createcount;		/* how many created on this level */
      int killcount;		/* how many killed on this level */
      char *aim;		/* which tagged sprite to aim for, if set */
      ai_t aim_ai;		/* AI to use in aiming, if set */
   }

* Add [generator|trigger|aim] activation and inactivation to the shell
  as they are by default inactive:
  - activate <generator|trigger|aim tag>
  - inactivate <generator|trigger|aim tag>
  With this it's even possible that another player starts later after
  certain trigger (time, first player death, whatever)...
  
  An example level:
  ---------------------------------------
  level_name "Zeppelin birds"
  description "Kill two zeppelins and then persist for 15 secs an assault of 
the birds to finish the level"
  # create two zeppelins to kill
  sprite zeppelin 200 400
  sprite zeppelin 600 400
  # start generating birds and aiming them at player...
  generator bird-generator bird 400 300 random 200 50
  trigger bird-timer bird-generator timer 500 50
  aim bird-aim bird p1plane
  # ...and finish level in 15 secs...
  trigger level-timer level-done timer 15000
  # ...once the two zeppelins have been killed
  trigger end-trigger bird-aim,bird-timer,level-timer,level-winner 
spritekill zeppelin 2
  activate end-trigger
  # create player
  generator player1 biplane 400 50 player 1 p1plane
  activate player1
  # level failure
  trigger fail-trigger level-fail playeralive 0
  --------------------------------------

I think this will be fairly straightforward to do with the new object
system, but it will require quite a lot of work...


	- Eero