From e951439bedec86d90df8022c52691101d234b197 Mon Sep 17 00:00:00 2001
From: alyosha-tas <alexei.f.k@gmail.com>
Date: Sun, 3 Dec 2017 19:09:33 -0500
Subject: [PATCH] GBHawk: Implement frame draw delay

---
 .../Consoles/Nintendo/GBHawk/GBHawk.IEmulator.cs  | 15 +++++++++++++--
 .../Consoles/Nintendo/GBHawk/PPU.cs               | 11 +++++++++--
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/GBHawk.IEmulator.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/GBHawk.IEmulator.cs
index af6cc525d9..ec2ea73c89 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/GBHawk.IEmulator.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/GBHawk.IEmulator.cs
@@ -116,7 +116,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			}
 			
 
-			while (!vblank_rise && (ticker < 100000))
+			while (!vblank_rise)
 			{
 				audio.tick();
 				timer.tick_1();
@@ -133,7 +133,10 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				{
 					vblank_rise = true;
 				}
+
 				ticker++;
+				if (ticker > 10000000) { throw new Exception("ERROR: Unable to Resolve Frame"); }
+
 				in_vblank_old = in_vblank;
 			}
 
@@ -183,7 +186,15 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 		public int[] GetVideoBuffer()
 		{
-			return _vidbuffer;
+			if (ppu.blank_frame)
+			{
+				for (int i = 0; i < _vidbuffer.Length; i++)
+				{
+					_vidbuffer[i] = (int)color_palette[0];
+				}
+				ppu.blank_frame = false;
+			}
+			return _vidbuffer;		
 		}
 
 		public int VirtualWidth => 160;
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/PPU.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/PPU.cs
index aa741aaf84..41531f005b 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/PPU.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/PPU.cs
@@ -79,6 +79,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 		public int index_used;
 		public int sprite_ordered_index;
 		public int bottom_index;
+		public bool blank_frame;
 
 		// windowing state
 		public int window_counter;
@@ -126,6 +127,12 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						OAM_access_write = true;
 					}
 
+					if (!LCDC.Bit(7) && value.Bit(7))
+					{
+						// don't draw for one frame after turning on
+						blank_frame = true;
+					}
+
 					LCDC = value;
 					break; 
 				case 0xFF41: // STAT
@@ -176,7 +183,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				case 0xFF4B: // WX
 					window_x = value;
 					break;
-			}
+			}			
 		}
 
 		public void tick()
@@ -233,7 +240,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						}						
 					}
 
-
 					cycle = 0;
 					LY += LY_inc;
 					//Console.WriteLine(Core.cpu.TotalExecutedCycles);
@@ -1232,6 +1238,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			ser.Sync("index_used", ref index_used);
 			ser.Sync("sprite_ordered_index", ref sprite_ordered_index);
 			ser.Sync("bottom_index", ref bottom_index);
+			ser.Sync("blank_frame", ref blank_frame);
 
 			ser.Sync("window_counter", ref window_counter);
 			ser.Sync("window_pre_render", ref window_pre_render);