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Re:Distance to target check


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#1 altra4u   Members   -  Reputation: 122

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Posted 06 April 2012 - 01:03 PM

Hi
So normally a distance check would be done by simply doing distance < range check. So lets say distance between character a from character b.
However to optimize one would do d^2 < r^2 check.

However if one has to include the radius of each of the characters then the check would be
distance - characterradii < range where characterradii = raidusofa + radiusofb

I'm trying to think of some way where I could keep the squared optimization and also be able to include the radii part.
Thoughts??
I'm discounting this one
(d^2 - r^2)/(d+r)
as that will need the square root value of d
Thanks.

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#2 Álvaro   Crossbones+   -  Reputation: 12940

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Posted 06 April 2012 - 01:12 PM

distance < range + sum_of_radii

distance^2 < range^2 + 2*range*sum_of_radii + sum_of_radii^2

You should be able to precompute everything on the right-hand side and then the check again becomes distance^2 < constant. So no square root needed.

#3 altra4u   Members   -  Reputation: 122

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Posted 06 April 2012 - 01:27 PM

Good suggestion.
Do you think its worth doing this addition and multiplication operations over doing square root of distance though?
Plus I will either have radius or radius^2. So if I have radius then I will have to square it and if I have radius^2 then I will have to root it. lol.
Or I would have to save both. Probably not a good idea to double data storage.

#4 altra4u   Members   -  Reputation: 122

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Posted 06 April 2012 - 01:36 PM

Basically I have distance^2, range^2 and radius of each character and I want to keep it the most optimized.
Looks like its going to have to be d - r < range check.

#5 Álvaro   Crossbones+   -  Reputation: 12940

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Posted 06 April 2012 - 02:15 PM

Multiplications and additions are much cheaper than square roots. Don't bother storing the squares of numbers, because they are easy to compute.




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