dos33fsprogs/hellmood_memories/tunnel.s
2020-05-07 15:22:06 -04:00

199 lines
2.8 KiB
ArmAsm

; Tunnel, based on the code in Hellmood's Memories
; by deater (Vince Weaver) <vince@deater.net>
; Zero Page
COLOR = $30
XCOORD = $F0
YCOORD = $F1
DEPTH = $F2
VALUE = $F6
M1 = $F7
M2 = $F8
FRAME = $F9
TEMP = $FA
; Soft Switches
KEYPRESS= $C000
KEYRESET= $C010
SET_GR = $C050 ; Enable graphics
FULLGR = $C052 ; Full screen, no text
; ROM routines
PLOT = $F800 ; plot, horiz=y, vert=A (A trashed, XY Saved)
SETCOL = $F864
SETGR = $FB40
tunnel:
;===================
; init screen
jsr SETGR ; 3
bit FULLGR ; 3
tunnel_forever:
inc FRAME ; 2
ldx #47 ; 2
yloop:
ldy #39 ; 2
xloop:
; Xcoord = (x-10)*4
sec ; 1
tya ; 1
sbc #10 ; 2
asl ; 1
asl ; 1
sta XCOORD ; 2
; Ycoord = (y-10)*4
sec ; 1
txa ; 1
sbc #10 ; 2
asl ; 1
asl ; 1
; center
sbc #24
sta YCOORD ; 2
; set depth to -9 (move backwards)
lda #$f7 ; 2
sta DEPTH ; 2
fx5_loop:
; get ycoord
lda YCOORD ; 2
; 8x8 signed multiply of M1*DEPTH
;sta M1 ; 2
jsr imul ; 3
lda M2 ; 2
sta VALUE ; 2
; get xcoord
lda XCOORD ; 2
; add distance to projection (bend right)
clc ; 1
adc DEPTH ; 2
;sta M1 ; 2
; 8x8 signed multiply of M1*DEPTH
jsr imul ; 3
; do the calculation
dec DEPTH ; 2
beq putpixel ; 2 ; is this needed?
; load the yprojection
lda VALUE ; 2
; xor with the xprojection
eor M2 ; 2
; center walls around 0
clc ; 1
adc #$4 ; 2
; test with -8, see if wall hit
sta VALUE ; 2
and #$f8 ; 2
beq fx5_loop ; 2
putpixel:
; adjust color by frame and set
sec ; 1
lda DEPTH ; 2
sbc FRAME ; 2
eor VALUE ; 2
and #$7 ; 2
;adc #$20
jsr SETCOL ; 3
txa ; A==Y1 ; 1
jsr PLOT ; (X2,Y1) ; 3
dey ; 1
bpl xloop ; 2
dex ; 1
bpl yloop ; 2
bmi tunnel_forever ; 2
;=================================================
; A = M1
; DEPTH (preserve) is M2
imul:
stx TEMP ; save as we trash it
sta M1 ; get values in right place
lda DEPTH
sta M2
eor M1 ; calc if we need to adjust at end
; (++ vs +- vs -+ vs --)
php ; save status on stack
; if M1 negative, negate it
lda M1
bpl m1_positive
eor #$ff
clc
adc #0
m1_positive:
sta M1
; if M2 negative, naegate it
lda M2
bpl m2_positive
eor #$ff
clc
adc #0
m2_positive:
sta M2
;==================
; unsigned multiply
; factors in M1 and M2
lda #0
ldx #$8
lsr M1
clc
imul_loop:
bcc no_add
clc
adc M2
no_add:
ror
ror M1
dex
bne imul_loop
sta M2
; done, high result in factor2, low result in factor1
; adjust to be signed
; if m1 and m2 positive, good
; if m1 and m2 negative, good
; otherwise, negate result
plp ; restore saved pos/neg value
bpl done_result
negate_result:
sec
lda #0
sbc M1
lda #0
sbc M2
done_result:
sta M2
ldx TEMP
rts