dos33fsprogs/graphics/hgr/tiny_triangles/writing.s
2021-04-09 23:33:27 -04:00

110 lines
1.3 KiB
ArmAsm

GBASL = $26
GBASH = $27
HGRPAGE = $E6
HGR_BITS = $1C
HGR_X = $E0
HGR_Y = $E2
HGR_COLOR = $E4
TEMP = $FE
OLD = $FF
PAGE0 = $C054
PAGE1 = $C055
HGR = $F3E2
HGR2 = $F3D8
HCLR = $F3F2
HPLOT0 = $F457 ;; plot at (Y,X), (A)
WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
;.zeropage
;.globalzp xx_smc,yy_smc
tiny:
jsr HGR2 ; clear page1
; A is 0 after
tiny_yloop:
; lda #0
; sta XX ; XX doesn't really matter where starts
; sta YY ; start at top of screen
tiny_xloop:
txa
; lda xx_smc+1
;===============here
; and yy_smc+1
eor yy_smc+1
;===============================
; modulo 9
;===============================
; value in A
mod_9:
; Divide by 9
; 17 bytes, 30 cycles
; by Omegamatrix https://forums.nesdev.com/viewtopic.php?t=11336
sta OLD
sta TEMP
lsr
lsr
lsr
adc TEMP
ror
adc TEMP
ror
adc TEMP
ror
lsr
lsr
lsr
; A is ORIG/9, mod = OLD-(A*9)
sta TEMP
asl
asl
asl
clc
adc TEMP
eor #$ff
sec
adc OLD
;
; beq store_color
; lda #$7f
store_color:
sta HGR_COLOR
ldy #0
;xx_smc:
; ldx #0
yy_smc:
lda #0
jsr HPLOT0 ; plot at (Y,X), (A)
; at begin, stores A to HGR_Y
; X to HGR_X and Y to HGR_X+1
; destroys X,Y,A
; Y is XX/7
ldx HGR_X
inx
; inc xx_smc+1
bne tiny_xloop
inc yy_smc+1
bne tiny_xloop
; should we over-write brk handler to restart?