From 4b4cfed14dae9afe08ef178992fd6703a176932d Mon Sep 17 00:00:00 2001
From: sasuke-arcade <58130089+sasuke-arcade@users.noreply.github.com>
Date: Sun, 31 May 2020 01:59:31 +0900
Subject: [PATCH] Gaplus : modify source code comments and change dipswitch
 defaults (#6752)

gaplus.cpp updates: [sasuke-arcade]
- Modify source code comments and change dipswitch defaults
- Changed Extend's default settings to Namco's factory settings (5k/15k/15k every)
---
 src/mame/drivers/gaplus.cpp |  2 +-
 src/mame/video/gaplus.cpp   | 12 +++++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/mame/drivers/gaplus.cpp b/src/mame/drivers/gaplus.cpp
index 3188074a7e9..989ea60b2b1 100644
--- a/src/mame/drivers/gaplus.cpp
+++ b/src/mame/drivers/gaplus.cpp
@@ -364,7 +364,7 @@ static INPUT_PORTS_START( gaplus )
 	PORT_DIPNAME( 0x08, 0x08, "Round Advance" ) PORT_DIPLOCATION("SW2:5")
 	PORT_DIPSETTING(    0x08, DEF_STR( Off ) )
 	PORT_DIPSETTING(    0x00, DEF_STR( On ) )
-	PORT_DIPNAME( 0x07, 0x00, DEF_STR( Bonus_Life ) ) PORT_DIPLOCATION("SW2:6,7,8")
+	PORT_DIPNAME( 0x07, 0x07, DEF_STR( Bonus_Life ) ) PORT_DIPLOCATION("SW2:6,7,8")
 	PORT_DIPSETTING(    0x00, "30k 70k and every 70k" )
 	PORT_DIPSETTING(    0x01, "30k 100k and every 100k" )
 	PORT_DIPSETTING(    0x02, "30k 100k and every 200k" )
diff --git a/src/mame/video/gaplus.cpp b/src/mame/video/gaplus.cpp
index 0bb8cc252ca..0a98812a14a 100644
--- a/src/mame/video/gaplus.cpp
+++ b/src/mame/video/gaplus.cpp
@@ -117,6 +117,8 @@ TILE_GET_INFO_MEMBER(gaplus_base_state::get_tile_info)
 #define SPEED_1 1.0f
 #define SPEED_2 2.0f
 #define SPEED_3 3.0f
+
+/* starfield: top and bottom clipping size */
 #define STARFIELD_CLIPPING_X 16
 
 void gaplus_base_state::starfield_init()
@@ -247,7 +249,11 @@ void gaplus_base_state::starfield_render(bitmap_ind16 &bitmap)
 		int x = m_stars[i].x;
 		int y = m_stars[i].y;
 
-		/* Some stars in the second tier will flash erratically while changing their movements. */
+		/* Some stars in the second layer will flash erratically when changing their movements.
+		   (It is when at reverse scrolling stage or get elephant head.)
+		   This is based on a guess from the video output of the PCB.
+		   https://www.youtube.com/watch?v=_1x5Oid3uPg (3:35-, 13:12-)
+		   https://www.youtube.com/watch?v=vrmZAUJYXnI (3:14-, 12:40-) */
 		if (m_stars[i].set == 1 && m_starfield_control[2] != 0x85 && i % 2 == 0)
 		{
 			int bit = BIT(m_starfield_framecount + i, 3) ? 1 : 2;
@@ -384,12 +390,12 @@ WRITE_LINE_MEMBER(gaplus_base_state::screen_vblank)/* update starfields */
 				break;
 
 				case 0x9f:
-					/* scroll left (speed 2) */
+					/* scroll left (speed 3) */
 					stars[i].y += SPEED_3;
 				break;
 
 				case 0xaf:
-					/* scroll right (speed 1) */
+					/* scroll right (speed 3) */
 					stars[i].y -= SPEED_3;
 				break;
 			}