z80:Sprite Routines

Sprite Routines

The routine below is a routine that takes your 8 wide * X high sprite and then puts it in the screen buffer. It is commonly known as Ion PutSprite, by Joe Wingbermuehle. More routines can be found on [*http://ticalc.org TiCalc] (see links to your left), United Ti and Cemetech.

   putSprite:
   	ld	e,l
   	ld	h,$00
   	ld	d,h
   	add	hl,de
   	add	hl,de
   	add	hl,hl
   	add	hl,hl               ;Find the Y displacement offset 
   	ld	e,a
   	and	$07               ;Find the bit number
   	ld	c,a
   	srl	e
   	srl	e
   	srl	e
   	add	hl,de             ;Find the X displacement offset
   	ld	de,gbuf
   	add	hl,de
   putSpriteLoop1:
   sl1:	ld	d,(ix)             ;loads image byte into D
   	ld	e,$00
   	ld	a,c
   	or	a
   	jr	z,putSpriteSkip1
   putSpriteLoop2:
   	srl	d                  ;rotate to give out smooth moving
   	rr	e
   	dec	a
   	jr	nz,putSpriteLoop2
   putSpriteSkip1:
   	ld	a,(hl)
   	xor	d
   	ld	(hl),a
   	inc	hl
   	ld	a,(hl)
   	xor	e
   	ld	(hl),a              ;copy to buffer using XOR logic
   	ld	de,$0B
   	add	hl,de
   	inc	ix                   ;Set for next byte of image
   	djnz	putSpriteLoop1 
   	ret

As is probably apparent, this routine can be modified to not only XOR sprites, but also AND and OR. All you have to do is change the two XOR's to the appropriate function.

Animating Sprites

The routine below will animate two sprites by simply displaying the first sprite, erasing it, then displaying the second sprite, erasing it and finally repeat the loop. Remember that this code is for only 2 sprites. More can be added though. Note that this routine uses ion calls and will not function unless you are using the ion header. See Shells for more information.

   loop:
   ld ix,Sprite_address
   ld a,X_coordinate
   ld l,Y_coordinate
   ld b,Sprite_height
   call iputsprite8          ;Assuming your sprite is 8x8
   call ifastcopy
   
   ld ix,Sprite_address
   ld a,X_coordinate
   ld l,Y_coordinate
   ld b,Sprite_height
   call iputsprite8               ;erase
   
   ld ix,Sprite_address
   ld a,X_coordinate+1
   ld l,Y_coordinate
   ld b,Sprite_height
   call iputsprite8                ;draw and display your second sprite
   call ifastcopy
   
   ld ix,Sprite_address
   ld a,X_coordinate+1
   ld l,Y_coordinate
   ld b,Sprite_height
   call iputsprite8               ;erase
   jp loop

Thank you Fallen Ghost for your help with this code!

Another look at Animated Sprites

If you want to cut down on size or increase speed, there is another way to create animated sprites. Instead of having to erase each time, what you could do is add an extra sprite that's an XOR of two sprites: the layer previously displayed, and the next layer. Note that the first and last layers must be intact (what they would look like without XOR-ing to another layer).

Example:

   loop:
    ld ix,Layer1				;draw first layer as is everytime
    ld a,0
    ld l,0
    ld b,8
    call ionputsprite
    call ionfastcopy
     
    ld ix,XORLayer				;move onto next layer. Since it has the XORed part, no need to erase ("already done")
    ld a,0
    ld l,0
    ld b,8
    call ionputsprite
    call ionfastcopy
   
   ;... any other layers would look similar to the few lines of code above
   
    ld ix,Layer2				;Just need to erase last layer
    ld a,0
    ld l,0
    ld b,8
    call ionputsprite
   
    jr loop
    
   Layer1:
   .db $00,$7E,$B9,$CF,$CF,$B9,$7E,$00
   
   Layer2:
   .db $FC,$72,$9E,$9E,$72,$FC,$00,$00
   
   XORLayer:							;XOR of Layer1 and Layer2
   .db $FC,$0C,$27,$51,$BD,$45,$7E,$00
   
   ;... extra XORed layers, if necessary

Calculating from above, having to erase each time took 13 bytes/extra layer, and some time (usually insignificant, but sometimes crucial). By having the XOR layer, it only adds 8 more bytes (assuming you have 8*8 sprites), and takes less time (if time is crucial). That's a saving of 5 bytes/extra layer!

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