add bgm playback, scrolling based on bgm time

Scripts/Scenes/Play/Audio/BGM.cs

@@ -0,0 +1,46 @@
+using Godot;
+using Godot.Collections;
+using System;
+
+public partial class BGM : AudioStreamPlayer
+{
+	public void LoadFromUser(string path)
+	{
+		if (!path.StartsWith("user://"))
+		{
+			GD.Print("Tried to load audio that isn't in user directory.");
+			return;
+		}
+
+		var f = FileAccess.Open(path, FileAccess.ModeFlags.Read);
+		if (f == null)
+		{
+			GD.PrintErr($"Unable to open {path} for loading audio! {FileAccess.GetOpenError()}");
+			return;
+		}
+		GD.Print("hi");
+		var ext = path.Split('.')[^1].ToLower();
+		switch (ext)
+		{
+			case "mp3":
+				var mp3 = new AudioStreamMP3()
+				{
+					Data = f.GetBuffer((long)f.GetLength())
+				};
+				Stream = mp3;
+				break;
+			case "wav":
+			case "wave":
+				var wav = new AudioStreamWav()
+				{
+					Data = f.GetBuffer((long)f.GetLength())
+				};
+				Stream = wav;
+				break;
+			case "ogg":
+				// TODO: implement
+				GD.PrintErr("External OGGs not supported in Godot 4.1...");
+				break;
+		}
+	}
+}

Scripts/Scenes/Play/Audio/SFX.cs

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+using Godot;
+using System;
+
+public partial class SFX : Node
+{
+	// Called when the node enters the scene tree for the first time.
+	public override void _Ready()
+	{
+	}
+
+	// Called every frame. 'delta' is the elapsed time since the previous frame.
+	public override void _Process(double delta)
+	{
+	}
+}

Scripts/Scenes/Play/Play.cs

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+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection.PortableExecutable;
+using Godot;
+using WacK.Configuration;
+using WacK.Data.Chart;
+using WacK.Data.Mer;
+using WacK.Things.TunnelObjects;
+
+namespace WacK.Scenes
+{
+	public class PlayParameters
+	{
+		/* TODO: store song ID from internal database
+		public string songID;
+		public Difficulty diff;
+		*/
+		public string chartPath;
+		public string soundPath;
+
+		public PlayParameters(string chPath, string snPath)
+		{
+			chartPath = chPath;
+			soundPath = snPath;
+			GD.Print($"Chart: {chartPath}\nSound: {soundPath}");
+		}
+	}
+	public partial class Play : Node
+	{
+		// initialized by another scene, BEFORE loading this one!
+		public static PlayParameters playParams;
+
+		// TunnelObjects we can instantiate
+		public static PackedScene noteTouch = GD.Load<PackedScene>("res://Things/TunnelObjects/Notes/NoteTouch.tscn");
+		public static PackedScene noteHold = GD.Load<PackedScene>("res://Things/TunnelObjects/Notes/NoteHold.tscn");
+		public static PackedScene noteChain = GD.Load<PackedScene>("res://Things/TunnelObjects/Notes/NoteChain.tscn");
+
+		[ExportCategory("Audio")]
+		[Export]
+		private BGM bgmController;
+		[Export]
+		private SFX sfxController;
+
+		[ExportCategory("2D")]
+		[ExportSubgroup("2D Things")]
+		[Export]
+		public Control noteDisplay;
+		[Export]
+		public Control scrollDisplay;
+		[Export]
+		public Background background;
+
+		[ExportSubgroup("Out-of-bounds Viewports")]
+		[Export]
+		public Viewport mainViewport;
+		[Export]
+		public Viewport leftViewport;
+		[Export]
+		public Viewport rightViewport;
+
+		private Chart chart;
+
+		// base scroll speed, which we can apply multipliers on
+		public static readonly float BASE_PIXELS_PER_SECOND = 800;
+		public static float scrollPxPerSec
+		{
+			get
+			{
+				return BASE_PIXELS_PER_SECOND * PlaySettings.playSpeedMultiplier.Value;
+			}
+		}
+
+		public override void _Ready()
+		{
+			// so we can see objects outside of the 0-60min. region
+			leftViewport.World2D = mainViewport.World2D;
+			rightViewport.World2D = mainViewport.World2D;
+
+			// parse mer and create chart for current play
+			chart = new(playParams.chartPath);
+			RealizeChart();
+
+			// audio setup
+			bgmController.LoadFromUser(playParams.soundPath);
+			bgmController.Play();
+		}
+
+		/// <summary>
+		/// Instantiates necessary notes onto noteDisplay for the player to see.
+		/// </summary>
+		private void RealizeChart()
+		{	
+			foreach (var msNote in chart.playNotes)
+			{
+				foreach (var note in msNote.Value)
+				{
+					THNotePlay nNote;
+					switch (note.type)
+					{
+						case NotePlayType.HoldStart:
+							nNote = noteHold.Instantiate<THNoteHold>();
+							((THNoteHold)nNote).InitHold((NoteHold)note, scrollDisplay);
+							break;
+						case NotePlayType.Touch:
+							nNote = noteTouch.Instantiate<THNotePlay>();
+							break;
+						case NotePlayType.Untimed:
+							nNote = noteChain.Instantiate<THNotePlay>();
+							break;
+						default:
+							continue;
+					}
+					nNote.Init(note);
+					var nPos = nNote.Position;
+					nPos.Y = msNote.Key * -scrollPxPerSec;
+					nNote.Position = nPos;
+					noteDisplay.AddChild(nNote);
+				}
+			}
+		}
+
+        public override void _Process(double delta)
+        {
+			double time = bgmController.GetPlaybackPosition() + AudioServer.GetTimeSinceLastMix() - AudioServer.GetOutputLatency();
+			
+			var nPos = noteDisplay.Position;
+			nPos.Y = ((float)time * scrollPxPerSec) + 1920;
+			noteDisplay.Position = nPos;
+			scrollDisplay.Position = nPos;
+        }
+
+        private void OnDestroy()
+		{
+			playParams = null;
+		}
+	}
+}