dos33fsprogs/megademo/island_lookup.s
Vince Weaver d208ea0cd3 megademo: add in mode7 code
this might be ill-advised
2018-10-02 23:04:51 -04:00

64 lines
1.4 KiB
ArmAsm

;====================================
; do a full lookup, takes much longer
; used to be a separate function but we inlined it here
;====================
; lookup_map
;====================
; finds value in space_x.i,space_y.i
; returns color in A
; CLOBBERS: A,Y
lda SPACEX_I ; 3
sta spacex_label+1 ; self modifying code, LAST_SPACEX_I ; 4
and #CONST_MAP_MASK_X ; wrap at 64 ; 2
sta SPACEX_I ; store i patch out ; 3
tay ; copy to Y for later ; 2
lda SPACEY_I ; 3
sta spacey_label+1 ; self modifying code, LAST_SPACEY_I ; 4
and #CONST_MAP_MASK_Y ; wrap to 64x64 grid ; 2
sta SPACEY_I ; 3
asl ; 2
asl ; 2
asl ; multiply by 8 ; 2
clc ; 2
adc SPACEX_I ; add in X value ; 3
; only valid if x<8 and y<8
; SPACEX_I is also in y
cpy #$8 ; 2
;============
; 39
bcs @ocean_color ; bgt 8 ; 2nt/3
ldy SPACEY_I ; 3
cpy #$8 ; 2
;=============
; 7
bcs @ocean_color ; bgt 8 ; 2nt/3
tay ; 2
lda flying_map,Y ; load from array ; 4
bcc @update_cache ; 3
;============
; 11
@ocean_color:
and #$1f ; 2
tay ; 2
lda water_map,Y ; the color of the sea ; 4
;===========
; 8
@update_cache:
sta map_color_label+1 ; self-modifying ; 4
;===========
; 4
; rts ; 6