Authored by LitDev
I recently wrote a TechNet Wiki article describing how to manage arrays of sprites in a game.
For the full article see http://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
'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
