Creating Additional Sprites - Commodore Amiga Hardware Reference Manual

Ll:
L2.:
MOVE.B
ADD.B
SUBQ.B
BNE
MOVE.B
EOR.B
MOVE.B
MOVE.B
ADD.B
MOVE.B
BRA
D2,$25001
D5,D3
#l,Dl
L2
#194,Dl
#$FE,D5
D3,$25000
D3,D6
#6,D6
D6,$25002
VLOOP
; Write new HSTART value to sprite
;Increment vertical value
;Decrement vertical counter
;Oount exhausted, reset to 19-1
;Negate the increment value
; Write new VSTART value to sprite
;Must now calculate new VSTOP
;VSTOP always VSTART+6 for spaceship
; Write new VSTOP to sprite
jLoop forever
Creating Additional Sprites
To use additional sprites, you must create a data structure for each one and arrange the
display as shown in the previous section, naming the pointers SPRIPTH and SPRIPTL
for sprite DMA channel
1,
SPR2PTH and SPR2PTL for sprite DMA channel 2, and so
on.
Note that when you enable sprite DMA for one sprIte, you enable DMA for all the
sprites and place them all in automatic mode. Thus, you do not need to repeat this step
when using additional sprite DMA channels. Once the sprite DMA channels are enabled,
all eight sprite pointers must be initialized to either a real sprite or a safe null sprite. An
uninitialized sprite could cause spurious sprite video to appear.
Also, recall that each pair of sprites takes its color from different color registers, as
shown in table 4-3.
110 Sprite Hardware
Table 4-3: Color Registers for Sprite Pairs
Sprite Numbers Color Registers
o
and 1
2 and 3
4 and 5
6 and 7
17 - 19
21- 23
25 - 27
29 - 31