From 0910dc507ab928df5a70f29ce7414a5812baaa24 Mon Sep 17 00:00:00 2001
From: zeromus <zeromus@users.sf.net>
Date: Sun, 1 Jul 2012 08:26:30 +0000
Subject: [PATCH] improve (very coarsely; it isnt perfect) timing of
 swapbuffers process to at least sequence it correctly with regards to vblank.
 fixes #3538901 DBZ Kai Butouden 3d on character select

---
 desmume/src/NDSSystem.cpp | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/desmume/src/NDSSystem.cpp b/desmume/src/NDSSystem.cpp
index d84461eee..63323081b 100644
--- a/desmume/src/NDSSystem.cpp
+++ b/desmume/src/NDSSystem.cpp
@@ -1632,11 +1632,6 @@ static void execHardware_hstart()
 		//when the vcount hits 262, vblank ends (oam pre-renders by one scanline)
 		execHardware_hstart_vblankEnd();
 	}
-	else if(nds.VCount==191)
-	{
-		//when the vcount hits 191, the 3d vblank occurs (maybe because OAM doesnt need to run anymore, so we can power it down, and give the 3d as much time as possible?)
-		gfx3d_VBlankSignal();
-	}
 	else if(nds.VCount==192)
 	{
 		//turn on vblank status bit
@@ -1647,6 +1642,18 @@ static void execHardware_hstart()
 		if(T1ReadWord(MMU.ARM9_REG, 4) & 0x8) MMU.reg_IF_pending[ARMCPU_ARM9] |= (1<<IRQ_BIT_LCD_VBLANK);
 		if(T1ReadWord(MMU.ARM7_REG, 4) & 0x8) MMU.reg_IF_pending[ARMCPU_ARM7] |= (1<<IRQ_BIT_LCD_VBLANK);
 	}
+	else if(nds.VCount==193)
+	{
+		//for our purposes, this block of code is the ending of the swapbuffers process.
+		//it happens 392 system clocks after vblank. thats 392/6=65 dots -- not one scanline.
+		//however, for convenience, we're deferring it to this scanline until we find that it needs to be more detailed
+		//OR - until we restore proper emulation of 3d command timing.
+		//this is important for the character select in Dragon Ball Kai - Ultimate Butouden
+		//it seems if you allow the 3d to begin before the vblank, then it will get interrupted and not complete.
+		//the game needs to pick up the gxstat reg busy as clear after it finishes processing vblank.
+		//therefore, this can't happen until sometime after vblank
+		gfx3d_VBlankSignal();
+	}
 
 	//write the new vcount
 	T1WriteWord(MMU.ARM9_REG, 6, nds.VCount);