Amaze 2
; Amaze (fixed version) : 128-byte intro Wolfenstein 3D raycasting engine (fasm 1.70.03/WinXP 5.1.2600)
; fixed : 1)divide overflow error bug 2)flickering/tearing /w double-buffer 3)speed 4)viewpoint angle bug
; compatibility : XP/Win7 DOS ntvdm or size coding competition compliant systems (retrolandia.net/hugi/showthread.php?tid=4)
; credit : written by Olivier Poudade 2013 aka baudsurfer^red sector incorporated 1985 (olivier.poudade.free.fr)
; credit (auxilliary) : inspired by Justin Frankel^Nullsoft's 256-byte intro gaycast (www.1014.org/code)
; credit (auxilliary) ; original algorithm written by John Carmack^id Software (www.armadilloaerospace.com/n.x/johnc)
; credit (auxilliary) ; feedback (thank you) provided by Photon, Pirx, rain_strom, Sensenstahl, Shockwave, zorke
; greets : Adok, Frag, lordKelvin, Pirx, Rudi, Shockwave, y0bi
; shouts : dark bit factory forum users (www.dbfinteractive.com)
org 100h ; program startup : start binary at psp+256
pop cx ; program setup : startup assumed sp=fffeh / cx=[sp]=[fffeh]=0 / sp=sp+2=0
pop es ; program setup : es=[sp]=20cdh double-buffer / sp=sp+2=0
pop fs ; program setup : fs=[sp]=ff9fh=a000h-16=(mode 13h video memory)-16 / sp=sp+2 / [sp+2]=9a00h
mov al,13h ; program setup : set vga chained mode 320x256x8 and clear screen funtion
int 10h ; program setup : vga video bios api clear screen function
fldz ; maze angle : st0=ANGBEG
fldz ; maze angle : st0=ANGVAL st1=ANGBEG
BEGANG: es lodsb ; buffer to screen : al=[es:si++]
mov [fs:si+7d0fh],al ; buffer to screen : 7d0fh=32015b=middle of *this column's screen offset (width*height/2) with ff9fh fixup / si=[32335;32015]
loop BEGANG ; buffer to screen : 1st time cx=0=>no loop / after cx=[0ffffh;0]=[65535b;O] from "loop BEGANG"
salc ; clear buffer : al=cf=0 fixed palette index color pixel
dec cx ; clear buffer : cx-=1=>cx=0ffffh=65535b
rep stosb ; clear buffer : [es:di++]=0 65535 times
fadd dword [ANGADD] ; maze angle : st0=ANGVAL*ANGADD st1=ANGBEG / [cs:ANGADD]=3bb90372h=0.0056f as angle stepping
fld st0 ; maze angle : st0=ANGVAL*ANGADD st1=ANGVAL*ANGADD st2=ANGBEG
fld1 ; maze angle : st0=1 st1=ANGVAL*ANGADD st2=ANGVAL*ANGADD st3=ANGBEG
faddp st3,st0 ; maze angle : st0=ANGVAL*ANGADD st1=ANGVAL*ANGADD st2=ANGBEG++
mov bp,319 ; column to screen : bp=screen width-1=xloop viewport index
ADDANG: fadd dword [ANGADD] ; viewport angle : st0=(ANGVAL+ANGBEG)*ANGADD st1=ANGBEG*ANGADD st2=ANGBEG
fld st0 ; viewport angle : st0=(ANGVAL+ANGBEG)*ANGADD st1=(ANGVAL+ANGBEG)*ANGADD st2=ANGBEG*ANGADD st3=ANGBEG
fsincos ; viewport angle : st0=cos((ANGVAL+ANGBEG)*ANGADD) st1=sin((ANGVAL+ANGBEG)*ANGADD) st2=(ANGVAL+ANGBEG)*ANGADD st3=ANGBEG*ANGADD st4=ANGBEG
fld st4 ; viewport angle : st0=ANGBEG st1=cos((ANGVAL+ANGBEG)*ANGADD) st2=sin((ANGVAL+ANGBEG)*ANGADD) st3=(ANGVAL+ANGBEG)*ANGADD st4=ANGBEG*ANGADD st5=ANGBEG
fld st5 ; viewport angle : st0=ANGBEG st1=ANGBEG st2=cos((ANGVAL+ANGBEG)*ANGADD) st3=sin((ANGVAL+ANGBEG)*ANGADD) st4=(ANGVAL+ANGBEG)*ANGADD st5=ANGBEG*ANGADD st6=ANGBEG
mov cx,7e0h ; viewport angle : 07e0h=2016b=32*63 size of maze portion to cast
ADDRAY: fadd st0,st3 ; raycast depth : st0=ANGBEG+sin((ANGVAL+ANGBEG)*ANGADD) st1=ANGBEG st2=cos((ANGVAL+ANGBEG)*ANGADD) st3=sin((ANGVAL+ANGBEG)*ANGADD) st4=(ANGVAL+ANGBEG)*ANGADD st5=ANGBEG*ANGADD st6=ANGBEG
fist dword [si] ; raycast depth : [si]=ANGBEG+sin((ANGVAL+ANGBEG)*ANGADD)
fxch ; raycast depth : st0=ANGBEG st1=ANGBEG+sin((ANGVAL+ANGBEG)*ANGADD) st2=cos((ANGVAL+ANGBEG)*ANGADD) st3=sin((ANGVAL+ANGBEG)*ANGADD) st4=(ANGVAL+ANGBEG)*ANGADD st5=ANGBEG*ANGADD st6=ANGBEG
fadd st0,st2 ; raycast depth : st0=ANGBEG+cos((ANGVAL+ANGBEG)*ANGADD) st1=ANGBEG+sin((ANGVAL+ANGBEG)*ANGADD) st2=cos((ANGVAL+ANGBEG)*ANGADD) st3=sin((ANGVAL+ANGBEG)*ANGADD) st4=(ANGVAL+ANGBEG)*ANGADD st5=ANGBEG*ANGADD st6=ANGBEG
mov bx,[si] ; raycast depth : bh=[si+1]=ANGBEG+sin((ANGVAL+ANGBEG)*ANGADD)
fist dword [si] ; raycast depth : [si]=ANGBEG+cos((ANGVAL+ANGBEG)*ANGADD)
fxch ; raycast depth : st0=ANGBEG+sin((ANGVAL+ANGBEG)*ANGADD) st1=ANGBEG+cos((ANGVAL+ANGBEG)*ANGADD) st2=cos((ANGVAL+ANGBEG)*ANGADD) st3=sin((ANGVAL+ANGBEG)*ANGADD) st4=(ANGVAL+ANGBEG)*ANGADD st5=ANGBEG*ANGADD st6=ANGBEG
mov bl,[si+1] ; raycast depth : bl=[si+1]=ANGBEG+cos((ANGVAL+ANGBEG)*ANGADD)
cmp byte [bx],ah ; raycast depth : test map wall hit ([bx]=0) at ray from null bitmask in code segment
loopnz ADDRAY ; raycast depth : 1)if wall found exit raycast loop 2)ANGVAL++ 3)07e0h=2016b=32*63=maze portion to cast 4)else continue
RAYHIT: neg cx ; wall found : cx=[1;2016] equivalent / fixup divide overflow
add cx,7f0h ; wall found ; 07f0h=2032=32*63+16 / was add cx,10h when counter register increased
mov ax,[ANGMUL] ; depth to height : [cs:ANGMUL]=3bb9h=15289d as zscale divisor lower word
cwd ; depth to height : dx=0 divisor upper word
div cx ; depth to height : cx=divisor=distance ax=result=wall height/2 dx=remainder
mov cx,4 ; wall found : reset fpu stack state ...
POPFPU: fstp st0 ; wall found : ... from : st0=ANGBEG+sin((ANGVAL+ANGBEG)*ANGADD) st1=ANGBEG+cos((ANGVAL+ANGBEG)*ANGADD) st2=cos((ANGVAL+ANGBEG)*ANGADD) st3=sin((ANGVAL+ANGBEG)*ANGADD) st4=(ANGVAL+ANGBEG)*ANGADD st5=ANGBEG*ANGADD st6=ANGBEG
loop POPFPU ; wall found : ... to : st0=(ANGVAL+ANGBEG)*ANGADD st1=ANGBEG*ANGADD st2=ANGBEG
xchg ax,cx ; depth to height : ax=0 cx=result=wall height/2 (dx=remainder)
xchg ax,si ; height to screen : ax=previous column's lowest vertical pixel si=0 (dx=remainder)
mov di,bp ; height to screen : di= this column's xloop viewport index
cmp cx,3ch ; height to screen : clipping test (wall<120 ?)
ANGADD: jc ADDTEX ; height to screen : no clipping needed
ANGMUL: mov cx,3bh ; height to screen : clipping (-1 byte candidate with glitchy mov cl,3bh)
ADDTEX: mov ax,cx ; height to screen : note this is where ah is nulled for test byte [bx],ah above
ADDCOL: stosb ; column to screen : plot upper vertical pixel
sub di,321 ; column to screen : get next upper vertical pixel
mov [es:si+bp],al ; column to screen : plot lower vertical pixel
add si,320 ; column to screen : get next lower vertical pixel
loop ADDCOL ; column to screen : repeat until all pixels of *this column wall processed
dec bp ; column to screen : decrement screen column index
jnz ADDANG ; column to screen : repeat until all 320 columns [319,0] of this screen processed
fstp st0 ; maze angle : st0=ANGBEG*ANGADD st1=ANGBEG
loop BEGANG ; maze angle : process next frame / cx=0ffffh for next clear screen[ back to the prod ]