# per pixel collision calculating start position

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Hi I am currently implementing per pixel collision into my project. I have calculated the collision box where the overlap occur. I now need to get the part in my sprites where this box is positioned. So how do I calculate where the box is in the two sprites? Best Regards Andreas

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Here is some code from something I wrote just the other day:
	Dim As Integer x1,y1,x2,y2,Aw=_maskA.sprite->Width,Ah=_maskA.sprite->height,Bw=_maskB.sprite->width,Bh=_maskB.sprite->height	Dim As UInteger oAx,oAy,oBx,oBy	Dim As UInteger maxA,minA,maxB,minB	Select Case _Ax-_Bx		Case Is >0			If (_Ax>=_Bx+Bw)Then Return 0 'boxes don't overlap.			x1=_Ax			oAx=0			oBx=x1-_Bx		Case Is <=0			If (_Bx>=_Ax+Aw)Then Return 0 'boxes don't overlap.			x1=_Bx			oBx=0			oAx=x1-_Ax	End Select'	Print "1"	Select Case _Ay-_By		Case Is >0			If (_Ay>=_By+Bh)Then Return 0 'boxes don't overlap.			y1=_Ay			oAy=0			oBy=y1-_By		Case Is <=0			If (_By>=_Ay+Ah)Then Return 0 'boxes don't overlap.			y1=_By			oBy=0			oAy=y1-_Ay	End Select'	Print "2"	Select Case (_Ax+Aw)-(_Bx+Bw)		Case Is <=0			If (_Ax+Aw<=_Bx)Then Return 0 'boxes don't overlap.			x2=_Ax+Aw		Case Is >0			If (_Bx+Bw<=_Ax)Then Return 0 'boxes don't overlap.			x2=_Bx+Bw	End Select'	Print "3"	Select Case (_Ay+Ah)-(_By+Bh)		Case Is <=0			If (_Ay+Ah<=_By)Then Return 0 'boxes don't overlap.			y2=_Ay+Ah		Case Is >0			If (_By+Bh<=_Ay)Then Return 0 'boxes don't overlap.			y2=_By+Bh	End Select'	Print "4"	Dim As Integer dx=x2-x1,dy=y2-y1	If (dx<0)or(dy<0)Then		Return 0 'no collision	EndIf

Notes:
' is the comment mark.
Select case/end case is a switch.
_Ax,_Ay is the position of the first sprite in the scene.
_Bx,_By is the position of the second sprite in the scene.
(x1,y1),(x2,y2) is the collision rectangle.
oAx,oAy are the offsets of where the collision box is located in the first sprite.
oBx,oBy are the offsets of where the collision box is located in the second sprite.

Return 0= no collision
Return -1 = collision (there is no return -1 in the above code :P)

I hope that helps ;)

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Thanks that worked out :)

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