eeh@public.UUCP (Eduardo E. Horvath eeh@btr.com) (07/13/90)
Hi! This is my first post form my new account! 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. Figuring out what octant you happen to be in seems to be a small problem. --------------------------------------------------------------------- Edurardo Horvath eeh@btr.com Look Ma, no sig! ---------------------------------------------------------------------
jms@tardis.Tymnet.COM (Joe Smith) (08/06/90)
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 BT Tymnet Tech Services | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms PO Box 49019, MS-C41 | BIX: smithjoe | 12 PDP-10s still running! "POPJ P," San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga speaks for me."