Type List Example

[kevin]

 This example requires PB1.61.  it shows how you can create native linked lists through typed variables.  Lists can not only store the parent type but any inherited children also. So it's linked collection.. :)
 

PlayBASIC Code: [Select]

   ; Limit the program to a max of 60 frames per second or less
   SetFPs 60


 ; Declare a type to hold all the properties of our BALL object
    Type Ball
      x#,y#
      angle#
      speed#
      Radius
      Colour
   Endtype
   
   ; Dimension the Typed Variable OBJECT with LIST support
   Dim Object as Ball list


   ; Start of main DO/LOOp
   Do

      ; Clear Screen to rgb(0,0,0)  (black)
         Cls rgb(0,0,0)
         print Fps()

      ; Check if the space key as pressed, if so, create a new ball
         if Spacekey() and FireTimer<Timer()
            Addball()
            FireTimer=Timer()+20
         endif

      ; PreLock the current buffer for a batch of 2D drawing
         Lockbuffer

         ; Draw and move all the objects in the list
            For Each Object()

               ; Move Object 
               x#=CosNewValue(Object.x,Object.angle,object.speed)
               y#=SinNewValue(Object.y,Object.angle,object.speed)
            
               ; Check if the move balls position is inside the default screen size
               if POintInBox(x#,y#,-50,-50,850,650)=false
                  ; if the point it outside this area, then it's left the screen
                  ; so we can delete it
               
                  Object = NULL      ;  Delete the current object 
                  Continue            ; Jump to the NEXT, so we avoid drawing a dead object
                  
               endif

               ; Store it's New position
               Object.x#=x#   
               Object.Y#=y#   

               ; Draw this ball as a filled coloured circle
               CircleC X#,Y#,Object.Radius,true,Object.COlour            

            next

      ; unlock the screen buffer
         unlockbuffer
      
      Sync         
   loop 



Function AddBall()

   ; Add a New Ball to the list
   Object = New Ball

   Object.X#      =Rnd(GetScreenWidth())
   Object.y#      =Rnd(GetScreenHeight())
   Object.Angle#   =rnd(360)
   Object.Speed#   =rndrange(2,10)
   Object.Radius   =rndrange(10,50)
   Object.Colour  =rndrgb()

EndFunction

[kevin]

 This is a variation of the above code, however this time we're dynamically managing sprites to be the graphical representations of our game characters.

PlayBASIC Code: [Select]

; Grab chunk of screen for as image for our sprites latter on. 
   CircleC 16,16,16,true,rgb(255,255,255)   ; drab a circle in white to the screen
   GetImage 1,0,0,32,32         ; grab the circle block from the screen as an image
   preparefximage 1         ; convert the image to an FX version, so it can be more easily rotated/tinted.
   
   


; Limit the program to a max of 60 frames per second or less
   SetFPs 60.7


 ; Declare a type to hold all of the properties of each object
    Type GameObject
      Sprite      ; sprite this object uses
      angle#      ; direction it's moving in
      speed#      ; speed it's moving at
      Colour      ; colour
   Endtype
   
   ; Dimension the Typed Variable OBJECT with LIST support
   Dim Object as GameObject list


   ; Start of main DO/LOOp
   Do

      ; Clear Screen to rgb(0,0,0)  (black)
         Cls rgb(0,0,0)
         
         Print "Press Space to Add Object to Scene"


      ; Check if the space key was pressed, if so, add a new character to the object list
         if Spacekey() and FireTimer<Timer()
            Addball()
            FireTimer=Timer()+20
         endif


         ; Run through and move all the objects in the list
            For Each Object()

               ; Get the sprite this object is using
                  ThisSprite=Object.Sprite

               ; Move Object 
                  x#=CosNewValue(GetSpriteX(ThisSprite),Object.angle,object.speed)
                  y#=SinNewValue(GetSpriteY(ThisSprite),Object.angle,object.speed)
            
               ; Check if the moved position is inside the default screen size ?
                  if POintInBox(x#,y#,-50,-50,850,650)=false

                     ; if the point it outside this area, then it's left the screen
                     ; so we can delete the sprite and the remove it's object from the list
                  
                     DeleteSprite Sprite
                  
                     ; Delete the  object in the list
                     Object = NULL      ;  Delete the current object 
                     Continue            ; Jump to the NEXT, so we avoid trying to position the deleted sprite bellow
                     
                  endif

               ; Set the sprites new position.
               PositionSprite ThisSprite,x#,y# 

            next


         ; Draw All Sprites 
            DrawAllSprites


      ; show the screen to the player               
      Sync         


   ; loop back to the DO statement to keep this program running
   loop 






Function AddBall()

   ; Add a New Ball to the list
   Object = New GameObject
   

   Object.Angle#   =rnd(360)            ; Get the direction this object is moving
   Object.Speed#   =rndrange(2,10)      ; Get the speed it'll be moving at
   Object.Colour  =rndrgb()


   x#=Rnd(GetScreenWidth())
   Y#=Rnd(GetScreenHeight())

   // Create sprite to represent this object visually
   ThisSprite=NewSprite(x#,y#,1)
   SpriteDrawMode ThisSprite,2
   SpriteTint ThisSprite,Object.Colour


   Object.Sprite   =ThisSprite

EndFunction

[frenchgui]

With Object=NULL line, the object still exists, is there a way to really delete it?

The function I use to count objects:

function countball()
   local i
   i=0
   for each object()
      inc i
   next
Endfunction i

[kevin]

With Object=NULL line, the object still exists, is there a way to really delete it?

Object=Null does delete it.

You could also use FreeCell.

[frenchgui]

OOOoops! Sorry you're right. My error was that I've typed object()=null instead of object=null. Thanks for your fast reply...