From 1b9372ff7c7580612721b0f1220473f513247bbe Mon Sep 17 00:00:00 2001
From: Frank Tovar <mail@franktovar.de>
Date: Sun, 10 May 2026 23:04:48 +0200
Subject: [PATCH] Restore dual terrain tilemap rendering

---
 .../MainWindow.xaml.cs                        | 89 ++++++++++++++++++-
 1 file changed, 85 insertions(+), 4 deletions(-)

diff --git a/src/ReactorMaintenance.Win2D/MainWindow.xaml.cs b/src/ReactorMaintenance.Win2D/MainWindow.xaml.cs
index 4c68a01..2b8b416 100644
--- a/src/ReactorMaintenance.Win2D/MainWindow.xaml.cs
+++ b/src/ReactorMaintenance.Win2D/MainWindow.xaml.cs
@@ -24,6 +24,11 @@ public sealed partial class MainWindow
         {
             return new(OriginX + (position.X * CellSize), OriginY + (position.Y * CellSize), CellSize, CellSize);
         }
+
+        public Rect DualTileRect(int x, int y)
+        {
+            return new(OriginX + ((x - 0.5) * CellSize), OriginY + ((y - 0.5) * CellSize), CellSize, CellSize);
+        }
     }
 
     private sealed record ForecastViewModel(string Message);
@@ -301,14 +306,84 @@ public sealed partial class MainWindow
 
     private void DrawTerrain(CanvasDrawingSession drawing, CanvasLayout layout)
     {
-        foreach (var position in AllPositions())
+        for (var y = 0; y <= m_Level.Height; y++)
         {
-            var rect = layout.CellRect(position);
-            var color = m_Level.GetTerrain(position) == ECellTerrain.Wall ? ColorHelper.FromArgb(255, 41, 47, 52) : ColorHelper.FromArgb(255, 32, 38, 42);
-            drawing.FillRectangle(rect, color);
+            for (var x = 0; x <= m_Level.Width; x++)
+                DrawDualTerrainTile(drawing, layout.DualTileRect(x, y), GetDualTileMask(x, y));
         }
     }
 
+    private void DrawDualTerrainTile(CanvasDrawingSession drawing, Rect rect, int floorMask)
+    {
+        if (m_TerrainTilemap is null)
+        {
+            DrawFallbackTerrainTile(drawing, rect, floorMask);
+            return;
+        }
+
+        var wallMask = c_AllCorners ^ floorMask;
+        drawing.DrawImage(m_TerrainTilemap, rect, TilemapSourceRect(wallMask), 1.0f, CanvasImageInterpolation.HighQualityCubic);
+    }
+
+    private static void DrawFallbackTerrainTile(CanvasDrawingSession drawing, Rect rect, int floorMask)
+    {
+        var color = floorMask == c_AllCorners ? ColorHelper.FromArgb(255, 32, 38, 42) : ColorHelper.FromArgb(255, 41, 47, 52);
+        drawing.FillRectangle(rect, color);
+    }
+
+    private static Rect TilemapSourceRect(int wallMask)
+    {
+        var tilePosition = wallMask switch {
+            c_BottomLeftCorner => new GridPosition(0, 0),
+            c_TopRightCorner | c_BottomRightCorner => new(1, 0),
+            c_TopLeftCorner | c_BottomLeftCorner | c_BottomRightCorner => new(2, 0),
+            c_BottomLeftCorner | c_BottomRightCorner => new(3, 0),
+            c_TopLeftCorner | c_BottomRightCorner => new(0, 1),
+            c_BottomLeftCorner | c_TopRightCorner | c_BottomRightCorner => new(1, 1),
+            c_AllCorners => new(2, 1),
+            c_TopLeftCorner | c_BottomLeftCorner | c_TopRightCorner => new(3, 1),
+            c_TopRightCorner => new(0, 2),
+            c_TopLeftCorner | c_TopRightCorner => new(1, 2),
+            c_TopLeftCorner | c_TopRightCorner | c_BottomRightCorner => new(2, 2),
+            c_BottomLeftCorner | c_TopLeftCorner => new(3, 2),
+            0 => new(0, 3),
+            c_BottomRightCorner => new(1, 3),
+            c_BottomLeftCorner | c_TopRightCorner => new(2, 3),
+            c_TopLeftCorner => new GridPosition(3, 3),
+            _ => throw new ArgumentOutOfRangeException(nameof(wallMask), wallMask, "Unsupported tile mask.")
+        };
+
+        return new(
+            tilePosition.X * c_TilemapTileSize,
+            tilePosition.Y * c_TilemapTileSize,
+            c_TilemapTileSize,
+            c_TilemapTileSize);
+    }
+
+    private int GetDualTileMask(int x, int y)
+    {
+        var mask = 0;
+        if (GetTerrainOrWall(x - 1, y - 1) == ECellTerrain.Floor)
+            mask |= c_TopLeftCorner;
+
+        if (GetTerrainOrWall(x, y - 1) == ECellTerrain.Floor)
+            mask |= c_TopRightCorner;
+
+        if (GetTerrainOrWall(x - 1, y) == ECellTerrain.Floor)
+            mask |= c_BottomLeftCorner;
+
+        if (GetTerrainOrWall(x, y) == ECellTerrain.Floor)
+            mask |= c_BottomRightCorner;
+
+        return mask;
+    }
+
+    private ECellTerrain GetTerrainOrWall(int x, int y)
+    {
+        var position = new GridPosition(x, y);
+        return m_Level.InBounds(position) ? m_Level.GetTerrain(position) : ECellTerrain.Wall;
+    }
+
     private void DrawUnderground(CanvasDrawingSession drawing, CanvasLayout layout)
     {
         foreach (var position in AllPositions())
@@ -908,6 +983,12 @@ public sealed partial class MainWindow
     private const double c_MaxZoom = 4;
     private const double c_ZoomStep = 1.15;
     private const double c_ClickPixelThreshold = 10;
+    private const int c_TilemapTileSize = 512;
+    private const int c_TopLeftCorner = 1;
+    private const int c_TopRightCorner = 2;
+    private const int c_BottomLeftCorner = 4;
+    private const int c_BottomRightCorner = 8;
+    private const int c_AllCorners = c_TopLeftCorner | c_TopRightCorner | c_BottomLeftCorner | c_BottomRightCorner;
     private static readonly Color c_FuelColor = ColorHelper.FromArgb(255, 220, 170, 68);
     private static readonly Color c_CoolantColor = ColorHelper.FromArgb(255, 57, 174, 196);
     private static readonly Color c_ElectricityColor = ColorHelper.FromArgb(255, 236, 226, 82);