river-raid: Routine at 7441

7441: Operate tank shell

Advances the tank shell along its trajectory and renders it. Shell moves in a parabolic arc based on speed and step count. Returns if shell not flying (bit 7 of tank_shell_state) Increments trajectory step, explodes at step 8 Plays descending pitch sound based on step Moves shell based on speed and orientation Renders shell sprite or triggers explosion
operate_tank_shell	7441	LD A,($7383)	Return if TANK_SHELL_BIT_FLYING not set.
	7444	BIT 7,A	Return if TANK_SHELL_BIT_FLYING not set.
	7446	RET Z
	7447	LD BC,($7385)	Load shell coords, increment trajectory step, store.
	744B	LD A,($7384)	Load shell coords, increment trajectory step, store.
	744E	INC A
	744F	LD ($7384),A
	7452	CP $08	If step == 8 (max), explode via render_tank_shell_explosion.
	7454	JP Z,render_tank_shell_explosion
	7457	LD DE,$0002	Play shell whistle: BEEPER with DE=$0002, HL=(step, 0).
	745A	LD H,A
	745B	LD L,$00
	745D	CALL $03B5
	7460	LD BC,($7385)	Reload shell coords, advance Y position, store to previous_object_coordinates.
	7464	CALL advance_object
	7467	LD ($8B0A),BC
	746B	LD A,($7383)	Get shell speed from state, add speed×2 to X position.
	746E	LD D,A
	746F	AND $07
	7471	LD E,A
	7472	LD A,C
	7473	ADD A,E
	7474	ADD A,E
	7475	LD C,A
	7476	BIT 6,D	If left-facing, invert X delta via invert_shell_coordinate_delta.
	7478	CALL NZ,invert_shell_coordinate_delta
	747B	INC B	Increment Y, store position to object_coordinates and tank_shell_coordinates.
	747C	LD ($8B0C),BC
	7480	LD ($7385),BC
	7484	LD A,$00	Set collision mode to COLLISION_MODE_NONE.
	7486	LD ($5EF5),A	Set collision mode to COLLISION_MODE_NONE.
	7489	LD A,B	Check viewport boundary. If off-screen, handle via erase_tank_shell_offscreen.
	748A	AND $88
	748C	CP $88
	748E	JP Z,erase_tank_shell_offscreen
	7491	LD HL,$8431	Render shell sprite: height=1, width=1, frame=$08.
	7494	LD DE,$0100
	7497	LD A,$01
	7499	LD BC,$0008
	749C	CALL render_sprite
	749F	RET