| ← D186 | Map | D20F → |
D1B9: Wheel behavior handler
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Runs the wheel each frame. It animates an 8-frame loop and follows its spawned heading.
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It bounces off solid tiles. It remembers its last vertical heading (up or down) in its logic record. While its heading is horizontal (right or left) the travel counter in its record ticks once per pass. At the eighth count it toggles the saved vertical heading between up and down and steers that way.
Every horizontal run starts from zero. The spawn clears the counter, and so does the wall-avoid bias each time a blocked probe sends the wheel horizontally toward the bat. A wheel blocked before its eighth count never flips. The counter does not tick while the wheel heads vertically. The result is a vertical zig-zag whose horizontal legs last at most eight passes.
It advances, and the far edge takes it. It runs no sweep, so only a ball kill can destroy it.
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| update_wheel | D1B9 | CALL inhabitant_react_state | Run the shared reaction machine; skip the update while a spawn or death animation plays. |
| D1BC | RET C | ||
| D1BD | LD HL,anim_wheel | Advance its 8-frame animation. | |
| D1C0 | CALL advance_anim | ||
| D1C3 | LD A,(IY+$0B) | Loop the animation, and wrap the frame at the end of its table. | |
| D1C6 | CP $08 | ||
| D1C8 | JR C,update_wheel_0 | ||
| D1CA | LD (IY+$0B),$00 | ||
| update_wheel_0 | D1CE | LD A,(IY+$00) | Is the heading vertical – straight up or straight down? |
| D1D1 | OR A | ||
| D1D2 | JR Z,update_wheel_1 | ||
| D1D4 | CP $04 | ||
| D1D6 | JR NZ,update_wheel_2 | ||
| update_wheel_1 | D1D8 | LD (IY+$0F),A | If so, save it as the last vertical direction. |
| update_wheel_2 | D1DB | LD A,(IY+$00) | Zig-zag only while the move is horizontal. |
| D1DE | CP $02 | ||
| D1E0 | JR Z,update_wheel_3 | ||
| D1E2 | CP $06 | ||
| D1E4 | JR NZ,update_wheel_6 | ||
| update_wheel_3 | D1E6 | INC (IY+$09) | Is this the frame that flips the heading? |
| D1E9 | LD A,(IY+$09) | ||
| D1EC | CP $08 | ||
| D1EE | JR NZ,update_wheel_6 | ||
| D1F0 | LD A,(IY+$0F) | A saved downward heading flips to up. | |
| D1F3 | CP $04 | ||
| D1F5 | JR NZ,update_wheel_4 | ||
| D1F7 | XOR A | ||
| D1F8 | JR update_wheel_5 | ||
| update_wheel_4 | D1FA | LD A,$04 | Anything else flips to down. |
| update_wheel_5 | D1FC | LD (IY+$00),A | Steer that way. |
| update_wheel_6 | D1FF | CALL object_avoid_walls | Bounce off walls, advance, and despawn off the far edge. |
| D202 | CALL move_object | ||
| D205 | CALL inhabitant_offscreen | ||
| D208 | RET C | ||
| D209 | LD B,$0A | A ball kill destroys it for 100 points; the result is ignored. | |
| D20B | CALL ball_kill | ||
| D20E | RET | ||
| ← D186 | Map | D20F → |