From 5f2d2851fe0ba3aa659b0afadfa4e05b13e0778b Mon Sep 17 00:00:00 2001
From: Souryo <mesenemu@gmail.com>
Date: Sat, 2 Jan 2016 18:02:56 -0500
Subject: [PATCH] Fixed PPU even_odd_timing test (when disabling BG just before
 cycle 339)

---
 Core/PPU.cpp | 11 ++++++++++-
 Core/PPU.h   |  1 +
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/Core/PPU.cpp b/Core/PPU.cpp
index 392e8d7b..b8064b07 100644
--- a/Core/PPU.cpp
+++ b/Core/PPU.cpp
@@ -31,6 +31,8 @@ PPU::~PPU()
 
 void PPU::Reset()
 {
+	_skipTick = false;
+
 	_state = {};
 	_flags = {};
 	_statusFlags = {};
@@ -536,11 +538,16 @@ void PPU::ProcessPrerenderScanline()
 			//copy vertical scrolling value from t
 			_state.VideoRamAddr = (_state.VideoRamAddr & ~0x7BE0) | (_state.TmpVideoRamAddr & 0x7BE0);
 		}
-	} else if(_nesModel == NesModel::NTSC && _cycle == 339 && IsRenderingEnabled() && (_frameCount & 0x01)) {
+	} else if(_nesModel == NesModel::NTSC && _cycle == 338 && IsRenderingEnabled() && (_frameCount & 0x01)) {
+		//Check for the cycle skip in the else if block below
+		//If, at cycle 338 in the prerender scanline, rendering is enabled, we skip a tick (cycle 340) on the current frame
+		_skipTick = true;
+	} else if(_cycle == 339 && _skipTick) {
 		//This behavior is NTSC-specific - PAL frames are always the same number of cycles
 		//"With rendering enabled, each odd PPU frame is one PPU clock shorter than normal" (skip from 339 to 0, going over 340)
 		_cycle = -1;
 		_scanline = 0;
+		_skipTick = false;
 	} else if(_cycle == 321 || _cycle == 329) {
 		LoadTileInfo();
 		if(_cycle == 329) {
@@ -785,6 +792,8 @@ void PPU::StreamState(bool saving)
 	Stream<uint16_t>(_spriteDmaAddr);
 	Stream<uint16_t>(_spriteDmaCounter);
 
+	Stream<bool>(_skipTick);
+
 	if(!saving) {
 		SetNesModel(_nesModel);
 	}
diff --git a/Core/PPU.h b/Core/PPU.h
index 3642bfc1..f81e8453 100644
--- a/Core/PPU.h
+++ b/Core/PPU.h
@@ -110,6 +110,7 @@ class PPU : public IMemoryHandler, public Snapshotable
 
 		NesModel _nesModel;
 		uint16_t _vblankEnd;
+		bool _skipTick;
 
 		PPUControlFlags _flags;
 		PPUStatusFlags _statusFlags;