OpenEuphoria

Re: Help with "facing" routine

• Posted by Jiri Babor <jbabor at PARADISE.NET.NZ> Jul 01, 1998
• 618 views

One or two more symmetries could be explored to further reduce the code
size, but I doubt it would result in any speed increase. Enjoy. Jiri


function determine_facing(sequence char_pos, sequence point)
    integer dx,dy,i
    atom raw_t,t
    dx=point[1]-char_pos[1]
    dy=point[2]-char_pos[2]
    if dy then                      -- if dy!=0
        raw_t=-dx/dy
        if raw_t>0 then t=raw_t else t=-raw_t end if
        -- 1st quadrant
        if t<0.1317 then i=1        -- tan( 7.5 deg)
        elsif t<0.4142 then i=2     -- tan(22.5 deg)
        elsif t<0.7673 then i=3     -- tan(37.5 deg)
        elsif t<1.3032 then i=4     -- tan(52.5 deg)
        elsif t<2.4142 then i=5     -- tan(67.5 deg)
        elsif t<7.5958 then i=6     -- tan(82.5 deg)
        else i=7
        end if
        if raw_t<0 then             -- 2nd or 4th quadrant
            if dy>0 then i=14-i     -- 2nd quadrant
            else                    -- 4th quadrant
                i=26-i
                if i=25 then i=1 end if
            end if
        elsif dy>0 then i=12+i      -- 3rd quadrant
        end if
    elsif dx>0 then i=7     -- horizontal, facing right
    else i=19               -- horizontal, facing left (or undetermined)
    end if
    return i
end function

-----Original Message-----
From: Einar Mogen <nord.staernes at ROLLAG.MAIL.TELIA.COM>
To: EUPHORIA at cwisserver1.mcs.muohio.edu
<EUPHORIA at cwisserver1.mcs.muohio.edu>
Date: Wednesday, 1 July 1998 10:45
Subject: Help with "facing" routine


>I would like some help on a function that should work like this:
>
>I pass it two sequences, the first one containing the coordinates of the
>active character, the second one containg the coordinates of the point that
>the active character should look at. I have a total of 24 facings, the
first
>one being directly up, the second 15 degrees to the right, the second 30
>degrees to the right, and so on. They are indexed 1-24. The function is
>supposed to return the facing index that most closely matches the character
>looking towards the point. If anyone out there which is more stable at
>mathematics like this could help me with the routine (it should be as fast
>as possible, since it will be called many times each frame of the game)
then
>I would be very grateful. I've started working on it, but now I'm both lazy
>and tired, and I'm not too keen on this kind of mathematics. Following is
an
>outline of the function:
>
>function determine_facing(sequence char_pos, sequence point)
>    -- find the closest match of the 24 possibilites
>    return facing -- 1 to 24
>end function
>
>Any help is greatly appreciated, the main thing I'm out for is the fastest
>way to find the angle which the point is at, relative to the character,
>either in degrees (or radians) or even better expressed with the indexes.
>
>Einar (who hopes his english is not _totally_ hopeless)
>