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2018-06-26 11:39

jamiefuller
Account closed

Registered: Mar 2018
Posts: 25

Simple "look at" function, avoiding atan2

Hi All,

I am writing a game that requires the player character to aim his gun at a movable point around the screen, I would usually calculate the angle using atan2 but don't want the overhead of a fully blown atan2 routine ( http://codebase64.org/doku.php?id=base:8bit_atan2_8-bit_angle )

The player can be any random x,y and the crosshaor can be any other random x,y

The gun sprite only needs to point in one of 8 directions so I can't help think that it must be easier to calculate/table. but I'm drawing a major blank :(

Any pointers or suggestions would be much appreciated.

Thanks

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2018-06-28 12:37

TWW

Registered: Jul 2009
Posts: 545

In which case you only need to LDA X1 CMP X2

2018-06-28 12:47

jamiefuller
Account closed

Registered: Mar 2018
Posts: 25

Quote: In which case you only need to LDA X1 CMP X2

Good point, and I had to double check my code to make sure :)

but in this case while I am not using dx later, I am using dx to calculate absdx, so I still need to do the subtraction to calculate dx, just not store it anywhere, only store absdx.

But I think I could probably do that for the last subtraction

        sec
        sbc absdx

which calculates absdy-absdx and only uses the sign of the output. I'll give it a try :)

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