Support weighted tile variantize (#18940)

* Support weighted tile variantize

* Remove unused using

* Use an array

Content.Shared/Maps/ContentTileDefinition.cs

@@ -1,5 +1,4 @@
 using Content.Shared.Atmos;
-using JetBrains.Annotations;
 using Robust.Shared.Audio;
 using Robust.Shared.Map;
 using Robust.Shared.Prototypes;
@@ -37,7 +36,7 @@ namespace Content.Shared.Maps
         public string BaseTurf { get; } = string.Empty;
 
         [DataField("canCrowbar")] public bool CanCrowbar { get; private set; }
-		
+
         /// <summary>
         /// Whether this tile can be pried by an advanced prying tool if not pryable otherwise.
         /// </summary>
@@ -62,7 +61,7 @@ namespace Content.Shared.Maps
         /// <summary>
         /// This controls what variants the `variantize` command is allowed to use.
         /// </summary>
-        [DataField("placementVariants")] public byte[] PlacementVariants { get; set; } = new byte[1] { 0 };
+        [DataField("placementVariants")] public float[] PlacementVariants { get; set; } = new [] { 1f };
 
         [DataField("thermalConductivity")] public float ThermalConductivity = 0.04f;
 

Content.Shared/Maps/TurfHelpers.cs

@@ -89,6 +89,30 @@ namespace Content.Shared.Maps
             return tile.Tile.IsSpace(tileDefinitionManager);
         }
 
+        /// <summary>
+        ///     Returns a weighted pick of a tile variant.
+        /// </summary>
+        public static byte PickVariant(this ContentTileDefinition tile, IRobustRandom? random = null)
+        {
+            IoCManager.Resolve(ref random);
+            var variants = tile.PlacementVariants;
+
+            var sum = variants.Sum();
+            var accumulated = 0f;
+            var rand = random.NextFloat() * sum;
+
+            for (byte i = 0; i < variants.Length; ++i)
+            {
+                accumulated += variants[i];
+
+                if (accumulated >= rand)
+                    return i;
+            }
+
+            // Shouldn't happen
+            throw new InvalidOperationException($"Invalid weighted variantize tile pick for {tile.ID}!");
+        }
+
         /// <summary>
         ///     Helper that returns all entities in a turf.
         /// </summary>