Table 7-2: Priority of Playfields Based on Values of Bits PF1P2-PF1P0
Value Placement
(from most important to least important)
000 PF1 SP01 SP23 SP45 SP67
001 SP01 PF1 SP23 SP45 SP67
010 SP01 SP23 PF1 SP45 SP67
011 SP01 SP23 SP45 PFl SP67
100 SP01 SP23 SP45 SP67 PFl
In this Table, PF1 stands for playfield 1, and SP01 stands for the group of sprites
numbered 0 and 1. SP23 stands for sprites 2 and 3 as a group; SP45 stands for sprites 4
and 5 as a group; and SP67 stands for sprites 6 and 7 as a group.
Bits PF2P2-PF2P0 let you position playfield 2 among the sprite priorities in exactly the
same way. However, it is the PF2PRI bit that determines which of the two playfields
appears in front of the other on the screen. Here is a sample of possible BPLCON2 register
contents that would create something a little unusual:
BITS 15-7 PF2PRI PF2P2-0 PF1P2-0
VALUE 0s 1 010 000
This will result in a sprite/playfield priority placement of:
PF1 SP01 SP23 PF2 SP45 SP67
In other words, where objects pass across each other, playfield 1 is in front of sprite 0 or
1; and sprites 0 through 3 are in front of playfield 2. However, playfield 2 is in front of
playfield 1 in any area where they overlap and where playfield 2 is not blocked by sprites
0 through 3.
Figure 7-3 shows one use of sprite/playfield priority. The single sprite object shown on the
diagram is sprite 0. The sprite can "fly" across playfield 2, but when it crosses playfield 1
the sprite disappears behind that playfield. The result is an unusual video effect that
causes the object to disappear when it crosses an invisible boundary on the screen.
- System Control Hardware 205 -
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