dos33fsprogs/mode7_demo/gr_putsprite.s

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;=============================================
; put_sprite
;=============================================
; Sprite to display in INH,INL
; Location is XPOS,YPOS
; Note, only works if YPOS is multiple of two?
put_sprite:
ldy #0 ; byte 0 is xsize ; 2
lda (INL),Y ; 5
sta CH ; xsize is in CH ; 3
iny ; 2
lda (INL),Y ; byte 1 is ysize ; 5
sta CV ; ysize is in CV ; 3
iny ; 2
lda YPOS ; make a copy of ypos ; 3
sta TEMPY ; as we modify it ; 3
;===========
; 28
put_sprite_loop:
sty TEMP ; save sprite pointer ; 3
ldy TEMPY ; 3
lda gr_offsets,Y ; lookup low-res memory address ; 5
clc ; 2
adc XPOS ; add in xpos ; 3
sta OUTL ; store out low byte of addy ; 3
lda gr_offsets+1,Y ; look up high byte ; 5
adc DRAW_PAGE ; ; 3
sta OUTH ; and store it out ; 3
ldy TEMP ; restore sprite pointer ; 3
; OUTH:OUTL now points at right place
ldx CH ; load xsize into x ; 3
;===========
; 36
put_sprite_pixel:
lda (INL),Y ; get sprite colors ; 5
iny ; increment sprite pointer ; 2
sty TEMP ; save sprite pointer ; 3
ldy #$0 ; 2
; check if completely transparent
; if so, skip
cmp #$0 ; if all zero, transparent ; 2
beq put_sprite_done_draw ; don't draw it ; 2nt/3
; FIXME: use BIT? ;==============
; 17
sta COLOR ; save color for later ; 3
; check if top pixel transparent
and #$f0 ; check if top nibble zero ; 2
bne put_sprite_bottom ; if not skip ahead ; 2nt/3
lda #$f0 ; setup mask ; 2
sta MASK ; 3
bmi put_sprite_mask ; 2nt/3
put_sprite_bottom:
lda COLOR ; re-load color ; 3
and #$0f ; check if bottom nibble zero ; 2
bne put_sprite_all ; if not, skip ahead ; 2nt/3
lda #$0f ; 2
sta MASK ; setup mask ; 3
put_sprite_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 ; 5
jmp put_sprite_done_draw ; we are done ; 3
put_sprite_all:
lda COLOR ; load color ; 3
sta (OUTL),Y ; and write it out ; 5
put_sprite_done_draw:
ldy TEMP ; restore sprite pointer ; 3
inc OUTL ; increment output pointer ; 5
dex ; decrement x counter ; 2
bne put_sprite_pixel ; if not done, keep looping ; 2nt/3
inc TEMPY ; each line has two y vars ; 5
inc TEMPY ; 5
dec CV ; decemenet total y count ; 5
bne put_sprite_loop ; loop if not done ; 2nt/3
rts ; return ; 6