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Determining heading on a grid

 
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Determining heading on a grid
rjolitz
post 4 Aug, 2008 - 04:49 PM
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Evening All.

I'm working on a browser based game for starship combat.

My plan, at this point, is to use a standard x y grid for positioning. What I'm not seeming to be able to figure out is how to figure what direction a ship will be facing based on movement.

using:

CODE


A .. B .. C
D .. .. .. E
F .. G .. H



A ship moving from (1,1) to (5,5) would be at heading H after that move. What I'm having trouble with is figuring out to determine that.

I'm working in PHP on this [suprise, suprise].

Can anyone kinda point me in the right direction on how to tackle this? I don't necessarily want the code [but won't turn it down] but some idea of a way to implement this.

Any help appreciated assuming this isn't clear as mud.
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AdamSpeight2008
post 4 Aug, 2008 - 05:09 PM
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The basics are
CODE

Xd=X1 - X0
Yd=Y1 - Y0
If Xd<0 and Yx<0 Then Return A
If Xd=0 and Yx<0 Then Return B
If Xd>0 and Yx<0 Then Return C
If Xd>0 and Yx=0 Then Return D
If Xd>0 and Yx>0 Then Return E
If Xd=0 and Yx>0 Then Return F
If Xd<0 and Yx>0 Then Return G
If Xd<0 and Yx=0 Then Return H
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NickDMax
post 4 Aug, 2008 - 05:19 PM
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Well it helps to look at this mathematically.

your change is x is (5 - 1) = 4 > 0 so you know you are moving easterly (C, E, H).

your change in y is (5 - 1) = 4 > 0 so you know you are moving in... well I assume a northly direction (F G H)

The intersection of the two sets is H.

OK -- so to crystallize this a little:

deltaX = (X_to - X_from);
deltaX = deltaX/abs(deltaX); //normalize
deltaY = (Y_to - Y_from);
deltaY = deltaY/abs(deltaY); //normalize

Now the deltas have 3 possible values -1, 0, 1

your grid is

A = (-1, 1)
B = (0, 1)
C = (1, 1)
D = (-1, 0)
E = (1, 0)
F = (-1, -1)
G = (0, -1)
H = (1, -1)
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