dos33fsprogs/demosplash2019/gr_overlay.s

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2019-11-05 03:47:52 +00:00
;=========================================================
; gr_overlay, 40x48 version
;=========================================================
; copy 0xc00 to DRAW_PAGE
; then overlay with 0x1000, treating 0xa as transparent
gr_overlay:
jsr gr_copy_to_current
gr_overlay_noload:
lda #40
sta CH ; xsize is in CH ; 3
lda #46
sta CV ; ysize is in CV ; 3
gr_overlay_custom:
ldy #0
gr_overlay_loop:
ldy CV ; 3
lda gr_offsets,Y ; lookup low-res memory address ; 4
sta OUTL ; store out low byte of addy ; 3
sta INL
lda gr_offsets+1,Y ; look up high byte ; 4
clc
adc DRAW_PAGE ; ; 3
sta OUTH ; and store it out ; 3
lda gr_offsets+1,Y ; look up high byte ; 4
clc
adc #$c ; force to start at $1000
sta INH
; OUTH:OUTL now points at right place
ldx CH ; load xsize into x ; 3
ldy #0
gr_overlay_put_pixel:
lda (INL),Y ; get sprite colors ; 5
; check if completely transparent
; if so, skip
cmp #$aa ; if all zero, transparent ; 2
beq gr_overlay_done_draw ; don't draw it ; 2nt/3
sta COLOR ; save color for later ; 3
; check if top pixel transparent
and #$f0 ; check if top nibble zero ; 2
cmp #$a0
bne gr_overlay_bottom ; if not skip ahead ; 2nt/3
lda COLOR
and #$0f
sta COLOR
lda #$f0 ; setup mask ; 2
sta MASK ; 3
bmi gr_overlay_mask ; always? ; 3
gr_overlay_bottom:
lda COLOR ; re-load color ; 3
and #$0f ; check if bottom nibble zero ; 2
cmp #$0a
bne overlay_put_sprite_all ; if not, skip ahead ; 2nt/3
;=============
; 7/8
lda COLOR
and #$f0
sta COLOR
lda #$0f ; 2
sta MASK ; setup mask ; 3
;===========
; 5
gr_overlay_mask:
lda (OUTL),Y ; get color at output ; 5
and MASK ; mask off unneeded part ; 3
ora COLOR ; or the color in ; 3
sta (OUTL),Y ; store it back ; 6
jmp gr_overlay_done_draw ; we are done ; 3
overlay_put_sprite_all:
lda COLOR ; load color ; 3
sta (OUTL),Y ; and write it out ; 6
gr_overlay_done_draw:
iny
dex ; decrement x counter ; 2
bne gr_overlay_put_pixel ; if not done, keep looping ; 2nt/3
dec CV ; decemenet total y count ; 5
dec CV
bpl gr_overlay_loop ; loop if not done ; 2nt/3
rts ; return ; 6