Fix map renderer error when painting decals with paths that start with /Textures (#16822)

Content.MapRenderer/Painters/DecalData.cs

@@ -2,17 +2,4 @@
 
 namespace Content.MapRenderer.Painters;
 
-public sealed class DecalData
-{
-    public DecalData(Decal decal, float x, float y)
-    {
-        Decal = decal;
-        X = x;
-        Y = y;
-    }
-
-    public Decal Decal;
-
-    public float X;
-    public float Y;
-}
+public readonly record struct DecalData(Decal Decal, float X, float Y);

Content.MapRenderer/Painters/DecalPainter.cs

@@ -28,7 +28,7 @@ public sealed class DecalPainter
         _sPrototypeManager = server.ResolveDependency<IPrototypeManager>();
     }
 
-    public void Run(Image canvas, List<DecalData> decals)
+    public void Run(Image canvas, Span<DecalData> decals)
     {
         var stopwatch = new Stopwatch();
         stopwatch.Start();
@@ -48,7 +48,7 @@ public sealed class DecalPainter
             Run(canvas, decal);
         }
 
-        Console.WriteLine($"{nameof(DecalPainter)} painted {decals.Count} decals in {(int) stopwatch.Elapsed.TotalMilliseconds} ms");
+        Console.WriteLine($"{nameof(DecalPainter)} painted {decals.Length} decals in {(int) stopwatch.Elapsed.TotalMilliseconds} ms");
     }
 
     private void Run(Image canvas, DecalData data)
@@ -67,7 +67,13 @@ public sealed class DecalPainter
         }
         else if (sprite is SpriteSpecifier.Rsi rsi)
         {
-            stream = _cResourceCache.ContentFileRead($"/Textures/{rsi.RsiPath}/{rsi.RsiState}.png");
+            var path = $"{rsi.RsiPath}/{rsi.RsiState}.png";
+            if (!path.StartsWith("/Textures"))
+            {
+                path = $"/Textures/{path}";
+            }
+
+            stream = _cResourceCache.ContentFileRead(path);
         }
         else
         {

Content.MapRenderer/Painters/GridPainter.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.InteropServices;
 using Content.Shared.Decals;
 using Robust.Client.GameObjects;
 using Robust.Shared.GameObjects;
@@ -57,7 +58,7 @@ namespace Content.MapRenderer.Painters
 
             // Decals are always painted before entities, and are also optional.
             if (_decals.TryGetValue(grid.Owner, out var decals))
-                _decalPainter.Run(gridCanvas, decals);
+                _decalPainter.Run(gridCanvas, CollectionsMarshal.AsSpan(decals));
 
 
             _entityPainter.Run(gridCanvas, entities);