Avoid zealously copying the entire video buffer

this might be larger than bufferwidth*bufferheight, and thus possibly dramantically decrease screenshot/dumping performance

src/BizHawk.Client.Common/QuickBmpFile.cs

@@ -187,7 +187,7 @@ public static unsafe void Copy(IVideoProvider src, IVideoProvider dst)
 		{
 			if (src.BufferWidth == dst.BufferWidth && src.BufferHeight == dst.BufferHeight)
 			{
-				Array.Copy(src.GetVideoBuffer(), dst.GetVideoBuffer(), src.GetVideoBuffer().Length);
+				Array.Copy(src.GetVideoBuffer(), dst.GetVideoBuffer(), src.BufferWidth * src.BufferHeight);
 			}
 			else
 			{

src/BizHawk.Client.Common/savestates/SavestateFile.cs

@@ -70,31 +70,19 @@ public void Create(string filename, SaveStateConfig config)
 
 			if (config.SaveScreenshot && _videoProvider != null)
 			{
-				var buff = _videoProvider.GetVideoBuffer();
-				if (buff.Length == 1)
+				var outWidth = _videoProvider.BufferWidth;
+				var outHeight = _videoProvider.BufferHeight;
+
+				// if buffer is too big, scale down screenshot
+				if (!config.NoLowResLargeScreenshots && outWidth * outHeight >= config.BigScreenshotSize)
 				{
-					// is a hacky opengl texture ID. can't handle this now!
-					// need to discuss options
-					// 1. cores must be able to provide a pixels VideoProvider in addition to a texture ID, on command (not very hard overall but interface changing and work per core)
-					// 2. SavestateManager must be setup with a mechanism for resolving texture IDs (even less work, but sloppy)
-					// There are additional problems with AVWriting. They depend on VideoProvider providing pixels.
+					outWidth /= 2;
+					outHeight /= 2;
 				}
-				else
-				{
-					int outWidth = _videoProvider.BufferWidth;
-					int outHeight = _videoProvider.BufferHeight;
 
-					// if buffer is too big, scale down screenshot
-					if (!config.NoLowResLargeScreenshots && buff.Length >= config.BigScreenshotSize)
-					{
-						outWidth /= 2;
-						outHeight /= 2;
-					}
-
-					using (new SimpleTime("Save Framebuffer"))
-					{
-						bs.PutLump(BinaryStateLump.Framebuffer, s => QuickBmpFile.Save(_videoProvider, s, outWidth, outHeight));
-					}
+				using (new SimpleTime("Save Framebuffer"))
+				{
+					bs.PutLump(BinaryStateLump.Framebuffer, s => QuickBmpFile.Save(_videoProvider, s, outWidth, outHeight));
 				}
 			}
 
@@ -222,13 +210,13 @@ private static void PopulateFramebuffer(BinaryReader br, IVideoProvider videoPro
 			}
 			catch
 			{
-				var buff = videoProvider.GetVideoBuffer();
+				var vb = videoProvider.GetVideoBuffer();
+				var vbLen = videoProvider.BufferWidth * videoProvider.BufferHeight;
 				try
 				{
-					for (int i = 0; i < buff.Length; i++)
+					for (var i = 0; i < vbLen; i++)
 					{
-						int j = br.ReadInt32();
-						buff[i] = j;
+						vb[i] = br.ReadInt32();
 					}
 				}
 				catch (EndOfStreamException)

src/BizHawk.Client.EmuHawk/AVOut/AviWriter.cs

@@ -124,7 +124,7 @@ private class VideoCopy : IVideoProvider
 
 			public VideoCopy(IVideoProvider c)
 			{
-				_vb = (int[])c.GetVideoBuffer().Clone();
+				_vb = c.GetVideoBufferCopy();
 				BufferWidth = c.BufferWidth;
 				BufferHeight = c.BufferHeight;
 				BackgroundColor = c.BackgroundColor;

src/BizHawk.Client.EmuHawk/AVOut/FFmpegWriter.cs

@@ -195,7 +195,7 @@ public void AddFrame(IVideoProvider source)
 			var video = source.GetVideoBuffer();
 			try
 			{
-				_muxer.WriteVideoFrame(video);
+				_muxer.WriteVideoFrame(video.AsSpan(0, _width * _height));
 			}
 			catch
 			{

src/BizHawk.Client.EmuHawk/AVOut/NutMuxer.cs

@@ -2,6 +2,7 @@
 using System.Text;
 using System.IO;
 using System.Numerics;
+using System.Runtime.InteropServices;
 
 namespace BizHawk.Client.EmuHawk
 {
@@ -538,15 +539,15 @@ public void WriteData(Stream dest)
 		/// <param name="video">raw video data; if length 0, write EOR</param>
 		/// <exception cref="Exception">internal error, possible A/V desync</exception>
 		/// <exception cref="InvalidOperationException">already written EOR</exception>
-		public void WriteVideoFrame(int[] video)
+		public void WriteVideoFrame(ReadOnlySpan<int> video)
 		{
 			if (_videoDone)
 				throw new InvalidOperationException("Can't write data after end of relevance!");
 			if (_audioQueue.Count > 5)
 				throw new Exception("A/V Desync?");
-			int dataLen = video.Length * sizeof(int);
-			byte[] data = _bufferPool.GetBufferAtLeast(dataLen);
-			Buffer.BlockCopy(video, 0, data, 0, dataLen);
+			var dataLen = video.Length * sizeof(int);
+			var data = _bufferPool.GetBufferAtLeast(dataLen);
+			MemoryMarshal.AsBytes(video).CopyTo(data.AsSpan(0, dataLen));
 			if (dataLen == 0)
 			{
 				_videoDone = true;
@@ -643,12 +644,12 @@ public void Finish()
 		{
 			if (!_videoDone)
 			{
-				WriteVideoFrame(Array.Empty<int>());
+				WriteVideoFrame([ ]);
 			}
 
 			if (!_audioDone)
 			{
-				WriteAudioFrame(Array.Empty<short>());
+				WriteAudioFrame([ ]);
 			}
 
 			// flush any remaining queued packets

src/BizHawk.Client.EmuHawk/AVOut/NutWriter.cs

@@ -75,7 +75,7 @@ public void AddFrame(IVideoProvider source)
 				SetVideoParameters(source.BufferWidth, source.BufferHeight);
 			}
 
-			_current.WriteVideoFrame(source.GetVideoBuffer());
+			_current.WriteVideoFrame(source.GetVideoBuffer().AsSpan(0, _width * _height));
 		}
 
 		public void AddSamples(short[] samples)

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -2458,7 +2458,7 @@ private void AutohideCursor(bool hide)
 
 		public BitmapBuffer MakeScreenshotImage()
 		{
-			var ret = new BitmapBuffer(_currentVideoProvider.BufferWidth, _currentVideoProvider.BufferHeight, _currentVideoProvider.GetVideoBuffer().ToArray());
+			var ret = new BitmapBuffer(_currentVideoProvider.BufferWidth, _currentVideoProvider.BufferHeight, _currentVideoProvider.GetVideoBufferCopy());
 			ret.DiscardAlpha();
 			return ret;
 		}

src/BizHawk.Client.EmuHawk/movie/RecordMovie.cs

@@ -250,7 +250,7 @@ private void Ok_Click(object sender, EventArgs e)
 					movieToRecord.SavestateFramebuffer = Array.Empty<int>();
 					if (_emulator.HasVideoProvider())
 					{
-						movieToRecord.SavestateFramebuffer = (int[])_emulator.AsVideoProvider().GetVideoBuffer().Clone();
+						movieToRecord.SavestateFramebuffer = _emulator.AsVideoProvider().GetVideoBufferCopy();
 					}
 				}
 				else if (StartFromCombo.SelectedItem.ToString() is START_FROM_SAVERAM && _emulator.HasSaveRam())

src/BizHawk.Emulation.Common/Interfaces/Services/IVideoProvider.cs

@@ -10,6 +10,9 @@ public interface IVideoProvider : IEmulatorService
 	{
 		/// <summary>
 		/// Returns a frame buffer of the current video content
+		/// This might be a reference to a stored frame buffer
+		/// Only <see cref="BufferWidth"/> * <see cref="BufferHeight"/> pixels valid
+		/// (The buffer might be larger than such, so don't rely on <see cref="Array.Length"/>
 		/// </summary>
 		int[] GetVideoBuffer();
 
@@ -81,5 +84,19 @@ public static void PopulateFromBuffer(this IVideoProvider videoProvider, int[] f
 				b2[i] = b1[i];
 			}
 		}
+
+		/// <summary>
+		/// Obtains a copy of the video buffer
+		/// <see cref="IVideoProvider.GetVideoBuffer" /> may return a reference
+		/// and might be much larger than the reported <see cref="IVideoProvider.BufferWidth"/> * <see cref="IVideoProvider.BufferHeight"/> (to account for differing frame sizes)
+		/// so this should be used to get an explicit copy
+		/// </summary>
+		public static int[] GetVideoBufferCopy(this IVideoProvider videoProvider)
+		{
+			var vb = videoProvider.GetVideoBuffer();
+			var ret = new int[videoProvider.BufferWidth * videoProvider.BufferHeight];
+			vb.AsSpan(0, ret.Length).CopyTo(ret);
+			return ret;
+		}
 	}
 }