diff --git a/ootw/TODO b/ootw/TODO
index 6d930d09..cebe095f 100644
--- a/ootw/TODO
+++ b/ootw/TODO
@@ -31,6 +31,9 @@ alien guard behavior:
 gun behavior:
 	+ doors/walls should explode outward away from blast
 	  *unless* there is another door/wall behind it
+	+ laser should show sparks when hits shields/walls
+	+ shield cannot be placed if room/floor wrong
+	+ shield collapse animation if blown up with blast
 
 + L1
 	- underwater there is a water-motion effect
diff --git a/ootw/collision.s b/ootw/collision.s
index c8386a3a..c2f010e6 100644
--- a/ootw/collision.s
+++ b/ootw/collision.s
@@ -6,6 +6,7 @@
 	; far left limit is LEVEL_LEFT limit
 	; far right limit is LEVEL_RIGHT limit
 	; any LOCKED doors in the way also stop things
+	; FIXME: only door collision if on same level
 recalc_walk_collision:
 
 	lda	RIGHT_LIMIT
@@ -73,3 +74,116 @@ done_recalc_walk_right_collision:
 
 
 	rts
+
+
+
+
+
+	;=============================
+	;=============================
+	; calc_gun_right_collision
+	;=============================
+	;=============================
+	; far right limit is LEVEL_RIGHT
+	; any LOCKED or CLOSED doors stop things
+	; any shield stops things
+	; our friend stops things
+	; any enemies stop things
+
+calc_gun_right_collision:
+
+	lda	RIGHT_LIMIT
+	and	#$7f
+	sta	RIGHT_SHOOT_LIMIT
+
+	lda	NUM_DOORS
+	beq	done_calc_gun_right_collision
+
+calc_gun_right_doors:
+
+
+	ldx	#0
+calc_gun_right_loop:
+
+	lda	PHYSICIST_X
+
+	cmp	door_x,X
+	bcs	calc_gun_right_continue		; bge
+
+	lda	door_status,X
+	cmp	#DOOR_STATUS_LOCKED
+	beq	calc_gun_right_door_there
+	cmp	#DOOR_STATUS_CLOSED
+	bne	calc_gun_right_continue
+
+calc_gun_right_door_there:
+	; early exit
+	lda	door_x,X
+	sta	RIGHT_SHOOT_LIMIT
+	jmp	done_calc_gun_right_collision
+
+calc_gun_right_continue:
+	inx
+	cpx	NUM_DOORS
+	bne	calc_gun_right_loop
+
+done_calc_gun_right_collision:
+
+
+	rts
+
+
+
+	;=============================
+	;=============================
+	; calc_gun_left_collision
+	;=============================
+	;=============================
+	; far right limit is LEVEL_LEFT
+	; any LOCKED or CLOSED doors stop things
+	; any shield stops things
+	; our friend stops things
+	; any enemies stop things
+
+calc_gun_left_collision:
+
+	lda	LEFT_LIMIT
+	and	#$7f
+	sta	LEFT_SHOOT_LIMIT
+
+	lda	NUM_DOORS
+	beq	done_calc_gun_left_collision
+
+calc_gun_left_doors:
+
+
+	ldx	NUM_DOORS
+	dex
+calc_gun_left_loop:
+	lda	PHYSICIST_X
+
+	cmp	door_x,X
+	bcc	calc_gun_left_continue		; blt
+
+	lda	door_status,X
+	cmp	#DOOR_STATUS_LOCKED
+	beq	calc_gun_left_door_there
+	cmp	#DOOR_STATUS_CLOSED
+	bne	calc_gun_left_continue
+
+calc_gun_left_door_there:
+	; early exit
+	lda	door_x,X
+	sta	LEFT_SHOOT_LIMIT
+	jmp	done_calc_gun_left_collision
+
+calc_gun_left_continue:
+	dex
+	bpl	calc_gun_left_loop
+
+done_calc_gun_left_collision:
+
+
+	rts
+
+
diff --git a/ootw/laser.s b/ootw/laser.s
index d548bf06..44550283 100644
--- a/ootw/laser.s
+++ b/ootw/laser.s
@@ -54,6 +54,8 @@ fire_laser:
 
 laser_left:
 
+	jsr	calc_gun_left_collision
+
 	ldx	PHYSICIST_X
 	dex
 	stx	laser0_end
@@ -67,6 +69,8 @@ laser_left:
 
 laser_right:
 
+	jsr	calc_gun_right_collision
+
 	lda	PHYSICIST_X
 	clc
 	adc	#5
@@ -153,12 +157,14 @@ still_starting_left:
 laser_edge_detect_left:
 
 	lda	laser0_end
+	cmp	LEFT_SHOOT_LIMIT
 	bmi	disable_laser
 
 	lda	laser0_start
+	cmp	LEFT_SHOOT_LIMIT
 	bpl	no_move_laser
 
-	lda	#0
+	lda	LEFT_SHOOT_LIMIT
 	sta	laser0_start
 
 	jmp	no_move_laser
@@ -190,14 +196,14 @@ laser_edge_detect_right:
 
 	; detect if totally off screen
 	lda	laser0_start
-	cmp	#40
+	cmp	RIGHT_SHOOT_LIMIT
 	bcs	disable_laser
 
 	lda	laser0_end
-	cmp	#40
+	cmp	RIGHT_SHOOT_LIMIT
 	bcc	no_move_laser
 
-	lda	#39
+	lda	RIGHT_SHOOT_LIMIT
 	sta	laser0_end
 
 no_move_laser: