Setting The Priority Control Register - Commodore Amiga Hardware Reference Manual

Five possible positions can be chosen for each of the two "playfield fingers." For exam-
ple, you can place playfield 1 on top of sprites 0 and 1 (0), between sprites 0 and 1 and
sprites 2 and 3 (1), between sprites 2 and 3 and sprites 4 and 5 (2), between sprites 4
and 5 and sprites 6 and 7 (3), or beneath sprites 6 and 7 (4). You have the same possi-
bilities for playfield 2.
The numbers 0 through 4 shown in parentheses in the preceding paragraph are the
actual values you use to select the play field priority positions. See "Setting the Priority
Con trol Register" below.
You can also control the priority of playfield 2 relative to playfield
1.
This gives you
additional choices for the way you can design the screen priorities.
SETTING THE PRIORITY CONTROL REGISTER
This register lets you define how objects will pass in front of each other or hide behind
each other. Normally, playfield 1 appears in front of playfield 2. The PF2PRI bit rev-
erses this relationship, making playfield 2 more important. You control the video priori-
ties by using the bits in BPLCON2 (for "bit-plane control register number 2") as shown
in table 7-1.
Table 7-1: Bits in BPLCON2
Bit
Number Name
Function
15-7 Not used (keep at 0)
6 PF2PRI Playfield 2 priority
5-3 PF2P2 - PF2PO Playfield 2 placement with
respect to the sprites
2-0
PFIP2 - PFIPO Playfield 1 placement with
respect to the sprites
The binary values that you give to bits PFIP2-PFIPO determine where playfield 1
occurs in the priority chain as shown in table 7-2. This matches the description given in
the previous section.
200 System Con trol Hard ware