Allow modded Ouis to specify if they play custom mountain music

Celeste.Mod.mm/Mod/Everest/Everest.Loader.cs

@@ -777,11 +777,7 @@ internal static void ProcessAssembly(EverestModuleMetadata meta, Assembly asm, T
                     // we already are in the overworld. Register new Ouis real quick!
                     if (Engine.Instance != null && Engine.Scene is Overworld overworld && typeof(Oui).IsAssignableFrom(type) && !type.IsAbstract) {
                         Logger.Verbose("core", $"Instantiating UI from {meta}: {type.FullName}");
-
-                        Oui oui = (Oui) Activator.CreateInstance(type);
-                        oui.Visible = false;
-                        overworld.Add(oui);
-                        overworld.UIs.Add(oui);
+                        ((patch_Overworld) overworld).RegisterOui(type);
                     }
                 }
                 // We should run the map data processors again if new berry types are registered, so that CoreMapDataProcessor assigns them checkpoint IDs and orders.

Celeste.Mod.mm/Mod/UI/OuiPropertiesAttribute.cs

@@ -0,0 +1,19 @@
+using System;
+
+namespace Celeste.Mod.UI {
+    [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
+    public class OuiPropertiesAttribute : Attribute {
+        /// <summary>
+        /// Whether the mountain music for the current map should play in this menu.
+        /// </summary>
+        public bool PlayCustomMusic { get; }
+
+        /// <summary>
+        /// Configures extra properties for this Oui.
+        /// </summary>
+        /// <param name="playCustomMusic">A list of unique identifiers for this Backdrop.</param>
+        public OuiPropertiesAttribute(bool playCustomMusic = false) {
+            PlayCustomMusic = playCustomMusic;
+        }
+    }
+}

Celeste.Mod.mm/Patches/Overworld.cs

@@ -1,10 +1,18 @@
 #pragma warning disable CS0626 // Method, operator, or accessor is marked external and has no attributes on it
 
+using Celeste;
 using Celeste.Mod;
 using Celeste.Mod.Meta;
 using Celeste.Mod.UI;
+using Mono.Cecil;
 using Monocle;
+using MonoMod;
+using MonoMod.Cil;
+using MonoMod.InlineRT;
+using MonoMod.Utils;
+using System;
 using System.Collections.Generic;
+using System.Reflection;
 
 namespace Celeste {
     class patch_Overworld : Overworld {
@@ -14,6 +22,8 @@ class patch_Overworld : Overworld {
         private Snow3D Snow3D;
 #pragma warning restore CS0649
 
+        public Dictionary<Type, OuiPropertiesAttribute> UIProperties { get; set; }
+
         public patch_Overworld(OverworldLoader loader)
             : base(loader) {
             // no-op. MonoMod ignores this - we only need this to make the compiler shut up.
@@ -54,9 +64,7 @@ public override void Update() {
                     return;
                 }
 
-                if (SaveData.Instance != null && (IsCurrent<OuiChapterSelect>() || IsCurrent<OuiChapterPanel>()
-                    || IsCurrent<OuiMapList>() || IsCurrent<OuiMapSearch>() || IsCurrent<OuiJournal>())) {
-
+                if (SaveData.Instance != null && IsCurrent(o => UIProperties?.GetValueOrDefault(o.GetType())?.PlayCustomMusic ?? false)) {
                     string backgroundMusic = mountainMetadata?.BackgroundMusic;
                     string backgroundAmbience = mountainMetadata?.BackgroundAmbience;
                     if (backgroundMusic != null || backgroundAmbience != null) {
@@ -79,6 +87,35 @@ public override void Update() {
             }
         }
 
+        public bool IsCurrent(Func<Oui, bool> predicate) {
+            if (Current != null) {
+                return predicate(Current);
+            }
+            return predicate(Last);
+        }
+
+        public Oui RegisterOui(Type type) {
+            Oui oui = (Oui) Activator.CreateInstance(type);
+            oui.Visible = false;
+            Add(oui);
+            UIs.Add(oui);
+            UIProperties ??= new() {
+                { typeof(OuiChapterSelect), new(true) },
+                { typeof(OuiChapterPanel), new(true) },
+                { typeof(OuiMapList), new(true) },
+                { typeof(OuiMapSearch), new(true) },
+                { typeof(OuiJournal), new(true) }
+            };
+            foreach (OuiPropertiesAttribute attrib in type.GetCustomAttributes<OuiPropertiesAttribute>()) {
+                UIProperties[type] = attrib;
+            }
+            return oui;
+        }
+
+        [MonoModIgnore]
+        [PatchOverworldRegisterOui]
+        public new extern void ReloadMenus(StartMode startMode = StartMode.Titlescreen);
+
         public extern void orig_ReloadMountainStuff();
         public new void ReloadMountainStuff() {
             orig_ReloadMountainStuff();
@@ -108,3 +145,38 @@ private void restoreNormalMusicIfCustomized() {
         }
     }
 }
+
+namespace MonoMod {
+    /// <summary>
+    /// Adjust the Overworld.ReloadMenus method to use the RegisterOui function, rather than registering manually
+    /// </summary>
+    [MonoModCustomMethodAttribute(nameof(MonoModRules.PatchOverworldRegisterOuiFunction))]
+    class PatchOverworldRegisterOuiAttribute : Attribute { }
+
+    static partial class MonoModRules {
+        public static void PatchOverworldRegisterOuiFunction(ILContext il, CustomAttribute attrib) {
+            MethodDefinition registerOuiMethod = MonoModRule.Modder.Module.GetType("Celeste.Overworld").FindMethod(nameof(patch_Overworld.RegisterOui));
+            //MethodInfo registerOuiMethod = typeof(patch_Overworld).GetMethod(nameof(patch_Overworld.RegisterOui));
+
+            ILCursor c = new(il);
+            c.GotoNext(MoveType.Before,
+                instr => instr.MatchLdloc(4),
+                instr => instr.MatchCall("System.Activator", nameof(Activator.CreateInstance)));
+            // We have Oui oui = (Oui)Activator.CreateInstance(type);
+            // Replace the right side of the equals with our register function
+
+            // this.
+            c.EmitLdarg0();
+            // Skip past `type` argument
+            c.GotoNext().GotoNext();
+            c.Remove();
+            c.Remove();
+            // RegisterOui()
+            c.EmitCall(registerOuiMethod);
+            // Skip past the "Oui oui ="
+            c.GotoNext().GotoNext();
+            // The next 10 instructions are already present in RegisterOui and can be removed
+            c.RemoveRange(10);
+        }
+    }
+}