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.export _draw_lorcha
.import popax
; TODO: maybe replace position tables with mul40? see
; libsrc/atari/mul40.s, which is getting linked anyway
; because conio uses it.
; offset from start of screen for each ship position (0-9)
lorcha_pos_lo:
.byte <320, <328, <336, <344, <352
.byte <640, <648, <656, <664, <672
lorcha_pos_hi:
.byte >320, >328, >336, >344, >352
.byte >640, >648, >656, >664, >672
; Atari OS's pointer to start of screen RAM
SAVMSC = $58
; ZP working variables start at $d4, aka FR0 (floating point reg 0).
mask = $d4
displacement = $d5
destptr = $d6
; Lorcha (boat), a type of sailing vessel having a Chinese
; junk rig on a Portuguese or European style hull.
; Our lorcha is a 7x7 block of ATASCII characters. We're storing
; directly to screen RAM, so we use 'internal' codes.
; To edit the graphics, load up LORCHA.LST in atari800, with the H:
; device enabled, writable, set to current directory. Then edit the
; quoted strings in lines 10-70, and RUN the program. It will
; generate a new LORCHA.DAT, which must be 49 bytes long (so don't
; change the lengths of the strings in the BASIC code!)
lorcha_data:
.incbin "LORCHA.DAT"
; void __fastcall__ draw_lorcha(int which, int displacement, int mask);
_draw_lorcha:
sta mask ; stash mask (0 = normal, $80 = inverse)
jsr popax ; get displacement (0 = whole ship, 1..6 = sinking, 7 = blank)
sta displacement
jsr popax ; which ship position?
tax
; setup pointer to screen offset of upper left of ship
lda lorcha_pos_lo,x
clc
adc SAVMSC
sta destptr
lda lorcha_pos_hi,x
clc
adc SAVMSC+1
sta destptr+1
; first, draw any blank lines
ldx displacement ; are there any?
beq shiplineloop ; no, draw ship
blanklineloop:
lda #0 ; screen code for space
;ora mask ; apply mask ; don't need this here
ldy #6 ; ship is 7 columns wide (we count 6 to -1)
blankcolloop:
sta (destptr),y
dey
bpl blankcolloop
jsr bump_pointer ; add 40 (1 line) to dest pointer.
dex
bne blanklineloop
; X is now 0, however we got here.
shiplineloop:
lda displacement
cmp #7
beq done
ldy #0
shipcolloop:
lda lorcha_data,x
eor mask
sta (destptr),y
iny
inx
cpy #7
bne shipcolloop
jsr bump_pointer
inc displacement
clc
bcc shiplineloop
done:
rts
bump_pointer:
lda destptr
clc
adc #40
sta destptr
lda destptr+1
adc #0
sta 215
rts
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