From 87680e69f5e4803b3d20b8b954fc725d33904282 Mon Sep 17 00:00:00 2001
From: Nebuleon Fumika
Date: Mon, 14 Jan 2013 23:35:53 -0500
Subject: Handle a game switching BG modes in the middle of a frame, to hi-res
 and to lo-res. This fixes Seiken Densetsu 3.

---
 source/gfx.cpp | 42 +++++++++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 15 deletions(-)

(limited to 'source')

diff --git a/source/gfx.cpp b/source/gfx.cpp
index decd195..d2b8b6e 100644
--- a/source/gfx.cpp
+++ b/source/gfx.cpp
@@ -663,18 +663,9 @@ void S9xStartScreenRefresh ()
 			IPPU.Interlace = (Memory.FillRAM[0x2133] & 1);
 		if (Settings.SupportHiRes && (PPU.BGMode == 5 || PPU.BGMode == 6 || IPPU.Interlace))
 		{
-			if (PPU.BGMode == 5 || PPU.BGMode == 6 || IPPU.Interlace)
-			{
-				IPPU.RenderedScreenWidth = 512;
-				IPPU.DoubleWidthPixels = TRUE;
-				IPPU.HalfWidthPixels = FALSE;
-			}
-			else
-			{
-				IPPU.RenderedScreenWidth = 256;
-				IPPU.DoubleWidthPixels = FALSE;
-				IPPU.HalfWidthPixels = FALSE;
-			}
+			IPPU.RenderedScreenWidth = 512;
+			IPPU.DoubleWidthPixels = TRUE;
+			IPPU.HalfWidthPixels = FALSE;
 
 			if (IPPU.Interlace)
 			{
@@ -707,13 +698,13 @@ void S9xStartScreenRefresh ()
 				GFX.PPLx2 = GFX.PPL << 1;
 			}
 		}
-		else if (!Settings.SupportHiRes && (PPU.BGMode == 5))
+		else if (!Settings.SupportHiRes && (PPU.BGMode == 5 || PPU.BGMode == 6 || IPPU.Interlace))
 		{
+			IPPU.RenderedScreenWidth = 256;
+			IPPU.DoubleWidthPixels = FALSE;
 			// Secret of Mana displays menus with mode 5.
 			// Make them readable.
-			IPPU.DoubleWidthPixels = FALSE;
 			IPPU.HalfWidthPixels = TRUE;
-			IPPU.DoubleHeightPixels = FALSE;
 		}
 		else
 		{
@@ -3741,6 +3732,27 @@ void S9xUpdateScreen ()
 			}
 		}
     }
+    else if (!Settings.SupportHiRes)
+    {
+	if (PPU.BGMode == 5 || PPU.BGMode == 6 || IPPU.Interlace)
+	{
+		if (!IPPU.HalfWidthPixels)
+		{
+			// The game has switched from lo-res to hi-res mode part way down
+			// the screen. Hi-res pixels must now be drawn at half width.
+			IPPU.HalfWidthPixels = TRUE;
+		}
+	}
+	else
+	{
+		if (IPPU.HalfWidthPixels)
+		{
+			// The game has switched from hi-res to lo-res mode part way down
+			// the screen. Lo-res pixels must now be drawn at FULL width.
+			IPPU.HalfWidthPixels = FALSE;
+		}
+	}
+    }
 	
     uint32 black = BLACK | (BLACK << 16);
 
-- 
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