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Message: 7089

Author: ian.rushforth

Date: 10/03/2017

Subject: Re: Arrows in JSW: Getting them in phase

 

Andrew wrote:

L = 287-R (mod 256)

Or in hex, L = #11F - R

And it works the other way around: R = #11F - L

I find that easier to get my head around, because if you end up with a value greater than #FF (255), the 'modulus' can be simply taken account of by just disregarding the 'hundreds' digit.

e.g. L to R arrow in original JSW: start position = #D0

To calculate the start position of a laterally-inverted arrow:

11F

- D0

= 4F

e.g. R to L arrow in original JSW: start position = #1C

To calculate the start position of a laterally-inverted arrow:

11F

- 1C

= 103

= 03 (drop the 'hundreds' digit)

P.S. Don't forget that the position where the arrow first appears, when Willy first enters a room, has been incremented or decremented along by one column before it is actually drawn to the screen!

 

 

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