Add comments to *set_oldnew_bg

InDevelopment/ManualUpdates/0.utf

@@ -342386,26 +342386,50 @@ return
 	mov %text_bg,0
 return
 
-
+; 'set_oldnew_bg' is meant to be used to display either a CG image or a fallback BG image
+; It's called 'set old new bg' because it's meant to either use the old or new style bg
+; depending on the %show_cgs, but in this script %show_cgs is always forced to 1
+; so the 'new' image (first argument) is always used.
+;
+; set_oldnew_bg [NEW_BG][OLD_BG][MODE][PRINT_EFFECT]
+;
+; Example usage: set_oldnew_bg e0301_a, Mdin_1b, 1, 23
+; NEW_BG: $witchh11 - The CG to display if CGs are enabled (NOTE: this function always has CGs enabled)
+; OLD_BG: $witchh12 - The fallback BG to display if CGs are disabled (This never happens)
+; MODE: %witchh13:
+;  - If 0: doesn't hide sprites when CG shown
+;  - If any other value: hides sprites
+;  - Additionally, if 2, uses the 'breakup' effect to display the CG
+;  - witchh13 is not used if CGs are disabled
+; PRINT_EFFECT: %witchh14 - The effect to use when displaying the BG and CG?
 *set_oldnew_bg
 	getparam $witchh11,$witchh12,%witchh13,%witchh14
-
+
+	; Someone has forced show_cgs to always be 1 whenever this function is called
 	mov %show_cgs,1
 
+	; Decide whether to hide sprites based on value of %witchh13
 	mov %witchh15,1
 	if %witchh13 = 0 mov %witchh15,0
 
+	; ------------ If "show_cgs" is enabled ------------
 	notif %show_cgs = 1 jumpf
+
+	; This line hides sprites while CG is displayed, until clr_oldnew_bg is called
 	mov %hide_new_sprites,%witchh15
 
+	; Display the BG
 	mov %oldnew_bg,1
 	mov $oldnew_bg,$witchh11
 	mov $oldnew_bg_old,$witchh12
-
 	gosub *displayOldNewBg
+
+	; Print the BG (either breakup effect or %witchh14 (4th arg) effect)
 	if %witchh13 = 2 print 99,2000,"breakup.dll/lrp"
 	notif %witchh13 = 2 print %witchh14
 	~
+
+	; ---- If "show_cgs" is NOT enabled, just display the regular background ($witchh12/2nd arg) ----
 	if %show_cgs = 1 jumpf
 		bg $witchh12,%witchh14
 	~