🚀 go-pugleaf

In article <259@public.UUCP> eeh@public.UUCP (Eduardo E. Horvath  eeh@btr.com) writes:
> 	Getting down to business:  Anyone know how the blitter octant bits
>decode?  They're called SUD, SUL, and AUL.  They are not laid out sequentially
>( i.e. binary values == octant numbers ) and they do not separate quadrants.

AUL = Always Up and Left, SUD = Sometimes Up or Down, SUL = Sometimes Up or
Left.  dx=abs(x1-x2), dy=abs(y1-y2).

From "Mapping the Amiga":
Bit 2: AUL (Always Up & Left) Set to 1 if ((dx >= dy) and (x1 >= x2)) or
       ((dx < dy) and (y1 >= y2)).
Bit 3: SUD Set if ((dx >= dy) and (y1 >= y2)) or ((dx < dy) and (x1 >= x2)).
Bit 4: SUL Set to 1 if dx >= dy.

From "ROM Kernel Manual - Hardware":  BLTCON1 code bits (4,3,2)    Octant #
            (2) | (1)                                    1 1 0        0
         --B3B2 | ----B2                                 0 0 1        1
(3) B4B3B2 \    |    / B4B2-- (0)                        0 1 1        2
        --------*--------                                1 1 1        3
(4) B4--B2 /    |    \ B4---- (7)                        1 0 1        4
         --B3-- | ------                                 0 1 0        5
            (5) | (6)                                    0 0 0        6
                                                         1 0 0        7
-- 
Joe Smith (408)922-6220 | SMTP: jms@tardis.tymnet.com or jms@gemini.tymnet.com
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