Spawning multiple instances of a sprite (firing bullets). Help needed.

Question

Hello there.  I'm currently trying to make a game in director 11.5 for a University project.  I've decided to make a scrolling space shooter but I've run into a problem.  Any tutorial I've found has created a limited 'bank' of bullets to fire, only allowing a certain number on the stage at any given time.  What I need to do is to leave a single bullet sprite off the boundaries of the page and essentially copy it and it's lingo behaviors to spawn another instance of the bullet on the stage when the player fires (using the left mouse button in this case).  I also need this copy to be deleted entirely when it collides with an enemy or leaves the boundaries of the stage, otherwise the game will just run slower and slower as more shots are fired.
I have heard that this is possible using the puppetSprite() method but the API doesn't shine much light on the issue and neither has literally hours of google searches.  If anyone can let me know any method of doing this, I'd be very grateful.
On a related issue, when fired the bullet will need to intsect the location of where the mouse cursor was when the bullet was fired and then continue on a linear path.  I've worked out a method of doing this but it isn't very effective or efficient (the speed of the bullets would be determined by how far away the mouse cursor is from the players ship and I think there's probably a less calculation intensive method for doing this) and as I can't spawn the bullets as of now, I really don't know if it will even work.  If anyone has any advice on how to better implement this mechanic, again I'd welcome your input.  Thanks in advance.

Answer 1

You want to work with objects not numbers which means using Points for locs and Sprite references and not sprite numbers.
I feel that using a object manager object would make programming this a lot easier, cleaner, and more efficient. Rather than give a lecture on OOP and OOD, I took some of Josh's ideas like using a timeout object and wrote some scripts in my style to give you something else to boggle your brain.
I tested these scripts but not thoroughly and I left plenty for you to do.
I separated out the creation and control of "bullets" from the movement of the bullets. So, there is a behavior that does nothing more than move the bullet sprites and the control object handles everything else using a single timeout object.
I suggest creating a new project to play with these scripts. Throw a bunch of sprites on the stage and attach the "Hitable Sprite" behavior to them, make sure you have a sprite named "bullet", and a " go the frame" behavior to loop on and you should be good to go.
Note that where I set the velocity of the bullet sprites, that I use "100.0" instead of 20.  20 would be a very fast speed.
Here's the Parent script for the control:
-- Bullet Control parent script
property  pUpdateTimer  -- timeout object for doing updates
property  pBullets  -- list of bullet sprites
property  pGunLoc  -- location of the gun, ie the location where your bullets start at.
property  pRightBounds  -- right edge of the stage
property  pBottomBounds  -- bottom edge of the state
property  pZeroRect  -- used for intersection hit detection
on new me
  pUpdateTimer = timeout().new("BulletCntrl", 25, #update, me)  -- 25 milleseconds = 40 updates per second
  pBullets = []
  pGunLoc = point(300,550)  -- *** SET THIS to where you want your bullets to start at.
  pZeroRect = rect(0,0,0,0)
  -- store stage bounds for later use
  pRightBounds = _movie.stage.rect.width
  pBottomBounds = _movie.stage.rect.height
  return me
end new
on fire me
  NewBullet = script("Bullet behavior").new(pGunLoc)  -- create new bullet sprite
  if ilk(NewBullet, #sprite) then pBullets.add(NewBullet)  -- store sprite reference
end fire
on update me, timeob
  if pBullets.count = 0 then exit  -- no bullets to update
  -- update bullet positions
  call(#update, pBullets)
  -- get list of sprites to test for hits/collisions
  HitSprites = []
  sendAllSprites(#areHitable, HitSprites)  -- the list "HitSprites" is populated by each hitable sprite.
  BulletsToDelete = []  -- list of bullet sprites to delete
  -- check if any bullet has hit a hitable sprite
  repeat with Bullet in pBullets
    repeat with HitSprite in HitSprites
      if Bullet.rect.intersect(HitSprite.rect) <> pZeroRect then
        HitSprite.explode()
        BulletsToDelete.add(bullet)
        exit repeat  -- leave inner loop
      end if
    end repeat
  end repeat
  -- check if bullet is out of bounds
  repeat with Bullet in pBullets
    Die = false
    if Bullet.right < 0 then Die = true
    if Bullet.left > pRightBounds then Die = true
    if Bullet.top > pBottomBounds then Die = true
    if Bullet.bottom < 0 then Die = true
    if Die then BulletsToDelete.add(Bullet)
  end repeat
  -- remove any sprites that hit something or went off the screen
  repeat with Bullet in BulletsToDelete
    Bullet.die()
    pBullets.deleteOne(Bullet)  -- remove bullet from list of active bullets
  end repeat
end update
on stopMovie
  -- end of app cleanup
  if pUpdateTimer.objectP then
    pUpdateTimer.forget()
    pUpdateTimer = void
  end if
end
The behavior for the bullets is:
-- Bullet behavior
property  pMe
property  pVelocity
property  pCurLoc
on new me, StartLoc
  -- get a sprite
  pMe = me.getSprite()
  if pMe.voidP then return void  -- if not a sprite then give up
  -- setup this bullet sprite
  pMe.puppet = true
  pMe.member = member("bullet")
  pMe.loc = StartLoc
  pMe.scriptInstanceList.add(me)  -- add this behavior to this sprite
  -- set velocity
  pVelocity = ( _mouse.mouseLoc - StartLoc) / 100.0  -- Note: magic number "20.0"
  updateStage()  -- need to update pMe.rect values
  pCurLoc = pMe.loc -- store current location
  return pMe  -- Note: returning "pMe" not "me"
end new
on getSprite me
  repeat with CurChannel = 1 to the lastchannel
    if sprite(CurChannel).member = (member 0 of castLib 0) AND sprite(CurChannel).puppet = false then
      return sprite(CurChannel)
    end if
  end repeat
  return void
end getSprite
on update me
  -- move bullet. 
  pCurLoc = pCurLoc + pVelocity  -- add velocity to pCurLoc to maintain floating point accuracy
  pMe.loc = pCurLoc 
end update
on die me
  pMe.scriptInstanceList = []  -- must manually clear this property
  pMe.puppet = false
end
We setup everything in a Movie script:
-- Movie Script
global gBulletCntrl
on prepareMovie
  gBulletCntrl = script("Bullet Control").new()
  the mouseDownScript = "gBulletCntrl.fire()"  -- route mouseDown events to the global object gBulletCntrl.
end prepareMovie
on stopMovie
  the mouseDownScript = ""
end stopMovie
Finally since we are shooting at other sprites we need a script on them to interact with the bullets.
--  Hitable Sprite Behavior
property  pMe
on beginSprite me
  pMe = sprite(me.spriteNum)
end beginSprite
on enterFrame me
  -- movie sprite
end enterFrame
on areHitable me, HitList
  HitList.add(pMe)
end areHitable
on explode me
  put "Boom"
end explode