Fix building turret rendering

Author: Rampastring

src/TSMapEditor/Rendering/ObjectRenderers/BuildingRenderer.cs

@@ -108,6 +108,28 @@ protected override bool ShouldRenderReplacementText(Structure gameObject)
             return base.ShouldRenderReplacementText(gameObject);
         }
 
+        protected override float GetDepthFromPosition(Structure gameObject, int bottomDrawPoint)
+        {
+            // As buildings can cover multiple cells and can also include turrets, the default implementation
+            // is not suitable. For example, sprites can be rendered southward of voxel turrets facing north, leading them
+            // the sprites to have higher depth and overlapping the voxel turrets.
+            //
+            // Instead, for buildings we calculate a positional depth value using the southernmost cell
+            // of the building's foundation. This depth value is identical for the base building sprite
+            // and turret, making it easy to draw the voxel either above or below the building
+            // by applying DepthEpsilon.
+            var southernmostCell = GetSouthernmostCell(gameObject);
+
+            int height = 0;
+            if (southernmostCell != null)
+            {
+                height = southernmostCell.Level;
+            }
+
+            return ((CellMath.CellTopLeftPointFromCellCoords(southernmostCell.CoordsToPoint(), Map).Y + Constants.CellSizeY) / (float)Map.HeightInPixelsWithCellHeight) * Constants.DownwardsDepthRenderSpace +
+                (height * Constants.DepthRenderStep);
+        }
+
         protected override float GetDepthAddition(Structure gameObject)
         {
             float buildingAdditionalDepth = gameObject.ObjectType.EditorZAdjust / (float)Map.HeightInPixelsWithCellHeight;

src/TSMapEditor/Rendering/ObjectRenderers/ObjectRenderer.cs

@@ -291,20 +291,23 @@ public virtual void DrawShadow(T gameObject)
             RenderDependencies.ObjectSpriteRecord.AddGraphicsEntry(new ObjectSpriteEntry(null, texture, drawingBounds, new Color(255, 255, 255, 128), false, true, depth));
         }
 
-        private float GetDepthFromPosition(T gameObject, int bottomDrawPoint)
+        protected virtual float GetDepthFromPosition(T gameObject, int bottomDrawPoint)
         {
-            var southernmostCell = Map.GetTile(gameObject.Position); // GetSouthernmostCell(gameObject);
+            // In this generic implementation, we only use the cell to fetch its height.
+            // Otherwise, position-related depth is calculated from the bottom draw point of the object.
+            var cell = Map.GetTile(gameObject.Position);
 
             int height = 0;
-            if (southernmostCell != null)
+            if (cell != null)
             {
-                height = southernmostCell.Level;
+                height = cell.Level;
             }
 
-            return ((bottomDrawPoint + Constants.CellSizeY) / (float)Map.HeightInPixelsWithCellHeight) * Constants.DownwardsDepthRenderSpace + (height * Constants.DepthRenderStep);
+            return ((bottomDrawPoint + (height * Constants.CellHeight) + Constants.CellSizeY) / (float)Map.HeightInPixelsWithCellHeight) * Constants.DownwardsDepthRenderSpace +
+                (height * Constants.DepthRenderStep);
         }
 
-        private MapTile GetSouthernmostCell(T gameObject)
+        protected MapTile GetSouthernmostCell(T gameObject)
         {
             MapTile tile = null;