Routines
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673D: Animate and render player missile
Missile speed: 6 pixels upward per frame. Called twice per frame for two-pass rendering (erase then draw).
On the first pass (missile_pass_selector = $01), adjusts missile position for screen scrolling. On both passes, moves missile up by 6 pixels.
If missile reaches top of screen (Y AND $F8 == 0), jumps to finalize_collision to finalize collision. Clears CONTROLS_BIT_FIRE_SOUND when missile is in lower screen area ($70 - Y >= 0).
Sets COLLISION_MODE_MISSILE so the rendering system checks for object collisions.
animate_plane_missile 673D LD A,($5EF3) Return if no missile active (Y == 0).
6740 CP $00
6742 RET Z
6743 LD BC,($5EF3) Backup coords to state_saved_object_coords; if first pass, adjust for scroll.
6747 LD ($5F8D),BC
674B LD A,($673C)
674E CP $01
6750 CALL Z,advance_object
6753 LD ($8B0A),BC Store previous position to previous_object_coordinates.
6757 LD BC,($5EF3) Calculate new position: X = plane_X + 4, Y = missile_Y - 6.
675B LD A,($5F72)
675E ADD A,$04
6760 LD C,A
6761 LD A,B
6762 SUB $06
6764 LD B,A If Y reached top of screen, jump to finalize_collision.
6765 AND $F8
6767 CP $00
6769 JP Z,finalize_collision (continued) Store new coordinates to state_plane_missile_y.
676C LD ($5EF3),BC
6770 LD A,$70 If missile in lower area, call clear_fire_bit to clear fire bit.
6772 SUB B
6773 CALL P,clear_fire_bit
6776 LD ($8B0C),BC Store position to object_coordinates.
677A LD A,$02 Set COLLISION_MODE_MISSILE in state_collision_mode.
677C LD ($5EF5),A
677F LD DE,$080C Set up sprite params and call render_sprite to render missile.
6782 LD HL,$8431
6785 LD BC,$0008
6788 LD A,$01
678A CALL render_sprite
678D RET
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