Sprite Arrays - Featured Article
I recently wrote a TechNet Wiki article describing how to manage arrays of sprites in a game.
For the full article see https://social.technet.microsoft.com/wiki/contents/articles/24857.small-basic-sprite-arrays.aspx.
The following is an excerpt from one section...
Recycling sprites
We often want sprites to appear and disappear. One way to do this is to recycle the sprites from a 'pool', activating and using them as required. This can be good for example to fire bullets or missiles, when we only ever need a limited number on screen at the same time.
The example below fires missiles when the mouse is clicked. A new spriteData property "Status" is used to flag that missiles are active or not. Inactive missiles are hidden and they are shown while they are active on the screen.
gw `` = ``600
gh `` = ``600
GraphicsWindow``.`` Width `` = ``gw
GraphicsWindow``.`` Height `` = ``gh
GraphicsWindow``.`` MouseDown `` = ``OnMouseDown
CreateSprites``(``)
'Game Loop
While ``(``"True"``)
`` start `` = ``Clock``.``ElapsedMilliseconds
`` If ``(``mouseDown`` ) ``Then
``FireMissile``(``)
`` mouseDown `` = ``"False"
``EndIf
``UpdateSprites``(``)
`` delay `` = `` 20 - ``(``Clock``.`` ElapsedMilliseconds `` - ``start``)
`` If ``(`` delay > ``0`` ) ``Then
``Program``.``Delay``(``delay``)
``EndIf
EndWhile
Sub ``CreateSprites
`` spriteImage `` = ``ImageList``.``LoadImage``(``"https://litdev.hostoi.com/game_images/missile.png"``)
``'Sprite dimensions we use the half width and height
`` spriteWidth `` = ``ImageList``.``GetWidthOfImage``(``spriteImage``)``/``2
`` spriteHeight `` = ``ImageList``.``GetHeightOfImage``(``spriteImage``)``/``2
`` numSprite `` = ``50
`` For `` i `` = 1 `` To ``numSprite
``spriteData``[``"image"`` ] `` = ``Shapes``.``AddImage``(``spriteImage``)
``spriteData``[``"Xpos"`` ] `` = `` spriteWidth `` + ``Math``.``GetRandomNumber``(``gw``-``2``*``spriteWidth``)
``spriteData``[``"Ypos"`` ] `` = ``gh``-``spriteHeight
``spriteData``[``"Xvel"`` ] `` = ``0
``spriteData``[``"Yvel"`` ] `` = ``-``5
``spriteData``[``"Status"`` ] `` = ``0
``Shapes``.``HideShape``(``spriteData``[``"image"``]``)
``sprites``[``i`` ] `` = ``spriteData
``EndFor
EndSub
Sub ``UpdateSprites
`` For `` i `` = 1 `` To ``numSprite
`` spriteData `` = ``sprites``[``i`` ] ``'get current sprite array
`` If ``(``spriteData``[``"Status"`` ] `` = ``1`` ) ``Then
``'Reposition sprite center
``spriteData``[``"Xpos"`` ] `` = ``spriteData``[``"Xpos"`` ] `` + ``spriteData``[``"Xvel"``]
``spriteData``[``"Ypos"`` ] `` = ``spriteData``[``"Ypos"`` ] `` + ``spriteData``[``"Yvel"``]
``'Move sprite center
``Shapes``.``Move``(``spriteData``[``"image"``]``,``spriteData``[``"Xpos"``]``-``spriteWidth``,``spriteData``[``"Ypos"``]``-``spriteHeight``)
``'Sprite finished with
`` If ``(``spriteData``[``"Ypos"`` ] `` < ``-``spriteHeight`` ) ``Then
``spriteData``[``"Status"`` ] `` = ``0
``Shapes``.``HideShape``(``spriteData``[``"image"``]``)
``EndIf
``sprites``[``i`` ] `` = `` spriteData ``'save updated sprite array (it may have been modified)
``EndIf
``EndFor
EndSub
Sub ``FireMissile
`` For `` i `` = 1 `` To ``numSprite
`` spriteData `` = ``sprites``[``i`` ] ``'get current sprite array
`` If ``(``spriteData``[``"Status"`` ] `` = ``0`` ) ``Then
``spriteData``[``"Status"`` ] `` = ``1
``Shapes``.``ShowShape``(``spriteData``[``"image"``]``)
``spriteData``[``"Xpos"`` ] `` = ``GraphicsWindow``.``MouseX
``spriteData``[``"Ypos"`` ] `` = ``gh``-``spriteHeight
``sprites``[``i`` ] `` = `` spriteData ``'save updated sprite array (it may have been modified)
`` i `` = `` numSprite ``'End loop
``EndIf
``EndFor
EndSub
Sub ``OnMouseDown
`` mouseDown `` = ``"True"
EndSub
