river-raid: Routine at 673D

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 deactivate_missile to deactivate missile. Clears SOUND_BIT_FIRE 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)	Save current position to state_saved_object_coords.
	6747	LD ($5F8D),BC	Save current position to state_saved_object_coords.
	674B	LD A,($673C)	If first pass, adjust position for scroll.
	674E	CP $01
	6750	CALL Z,advance_object
	6753	LD ($8B0A),BC	Store current position as previous for sprite erasure.
	6757	LD BC,($5EF3)	X = plane_X + 4.
	675B	LD A,($5F72)
	675E	ADD A,$04
	6760	LD C,A
	6761	LD A,B	Y = missile_Y - 6.
	6762	SUB $06
	6764	LD B,A
	6765	AND $F8	If missile reached top of screen, jump to deactivate_missile.
	6767	CP $00
	6769	JP Z,deactivate_missile
	676C	LD ($5EF3),BC	Store new missile position.
	6770	LD A,$70	If missile has risen to Y ≤ $70, stop fire sound.
	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	Set COLLISION_MODE_MISSILE in state_collision_mode.
	677F	LD DE,$080C	Set up sprite params.
	6782	LD HL,$8431
	6785	LD BC,$0008
	6788	LD A,$01
	678A	CALL render_sprite
	678D	RET