A86: Sprites

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A86: Sprites

Hello Guys - I wonder if anyone can tell me what is wrong w/this ?  I
stored 0 into landy and 0 into landx as a test, but the only way it works
is ld a,0 ld b,a , same w/c.  Why ?  Here is the part of the source ...
Please help if you can!

------------------------

dispLander:
	ld	a,(landy)
	ld	b,a
	ld	a,(landx)
	ld	c,a
	ld	hl,SHIP
	call	PutSpriteXOR
	ret

---------------------------

And here are the sprite routines and the sprite.

-----------------------------

PutSpriteXOR: ; Puts a sprite stored at (HL) at B,C
      push bc           ; save BC
      push de           ; save DE
      push hl   ; save HL
      push hl   ; save HL
      ld e,b
      ld d,c
      call FindPixel ; NOTE i did not include the FindPixel Routine..
                           ;its the one found on this list earlier!
      ld de,$FC00  ; DE points to VID MEM
      ex de,hl                  ; DE = VID MEM + PIXEL LOC
      pop hl                    ; HL = PIC LOC
      ld b,(hl)                 ; get first byte from PIC LOC (width)
      inc hl                    ; HL = next byte in PIC LOCATION
      ld c,(hl)                 ; get second byte from PIC LOC (height)
      inc hl                    ; HL = START OF PIC
      push hl                   ; save HL
      pop ix   ; IX = START OF PIC
      ex de,hl                  ; HL = VID MEM + PIXEK LOC DE = START OF
PIC
PS_NewRow:
      push bc                   ; save BC
      ld d,(ix)   ; D = next byte of PIC
      inc ix   ; IX points to next byte
      push af                   ; save AF
      push hl   ; save HL
PS_NewCol:
      rl d   ; Rotate Left D
      ld e,a   ; e = a
      jr nc,PS_NoPixel        ; if No Carry then goto NoPixel
      ;************ can be OR or XOR or AND or whatever :)  *****
      xor (hl)                   ; a = a or (hl)
      ;***************************************************
      ld (hl),a                 ; hl = hl or a (basically)
      jr PS_NextPixel
PS_NoPixel:
      cpl
      and (hl)
      ld (hl),a
PS_NextPixel:
      ld a,e                    ; get A back
      rrca                      ; rotate right circular
      jr nc,PS_SameByte  ; if no carry then same byte
      inc hl                    ; else HL points to next byte in PIC
PS_SameByte:
      djnz PS_NewCol            ; go to next column
      pop hl
      pop af
      ld de,16
      add hl,de
      pop bc
      dec c
      jr nz,PS_NewRow
      pop hl
      pop de
      pop bc
      ret

FindPixel:
        ld a,e
        and $07         ; a = bit offset
        ld b,0
        ld c,a
        ld hl,FP_Bits
        add hl,bc
        ld b,(hl)       ; b = bitmask for (hl)
;56 t-states up to this point
        ld a,d
        rlca            ; multiply y by 4
        rlca
        ld l,a
        ld h,0
        add hl,hl       ; multiply y by 4 again
        add hl,hl       ;   because there are 16 bytes in a pixel row
        ld a,e
        rrca            ; divide x by 8 (8 pixels/byte)
        rrca
        rrca
        and $0F
        ld c,a
        ld a,b          ; now a = bitmask for (hl)
        ld b,$FC
        add hl,bc       ; hl -> byte in LCD memory
;150 t-states up to this point
        ret
FP_Bits: .db $80,$40,$20,$10,$08,$04,$02,$01

;-----------------------------------------------------

SHIP:
   	.db 8,8
   	.db %00011000
   	.db %00100100
   	.db %00100100
   	.db %00100100
   	.db %01000010
   	.db %01011010
   	.db %11100111
   	.db %00011000

------------------------------------


Thanks.


Ahmed El-Helw
ahmed3@worldnet.att.net
http://ahmed1.home.ml.org
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