tile-health (#18)

Reviewed-on: #18

gdd.md

@@ -8,6 +8,11 @@
 * Education
 * Supply chains
 
+## Clock
+
+Ticks can be applied manually or they can be applied over time.
+Add a tick counter as a UI element.
+
 ## Grid
 
 Add a 10x10 grid.
@@ -17,13 +22,6 @@ Tiles are highlighted a different colour when the player hovers over them with t
 
 Tiles in the grid contain floating point values.
 These values propogate to neighbouring cells a tick happens.
-Ticks can be applied manually or they can be applied over time.
-Add a tick counter as a UI element.
-
-* [ ] understand different options for representing the rate of diffusion
-
-Diffusing should use 'pull' operations; tiles should pull values from surrounding tiles.
-This is an attempt to think forwards to parallelising computation of diffusiong - ideally using the GPU.
 
 #### Diffusion Algorithm
 
@@ -46,6 +44,20 @@ private float TransferHeat(float t0, float alpha, float nx, float ny, float px,
 }
 ```
 
+Diffusing uses 'pull' operations; tiles pull values from surrounding tiles.
+This is an attempt to think forwards to parallelising computation of diffusiong - ideally using the GPU.
+
+## Overlays
+
+The current overlay can be cycled with a UI button or by pressing `tab`.
+Overlays display tile information by displaying tiles in different colours.
+Normally, tile colours are displayed depending on their type and health.
+This is the 'normal' view with no overlay.
+
+Other overlays include:
+
+* [Heat overlay](#heat-overlay)
+
 ## Build Mode
 
 Build mode can be entered by pressing the `b` key.
@@ -71,8 +83,12 @@ In build mode, the player can click on a wile tile to turn it into a developed t
 
 Developed tiles produce heat while wild tiles absorb it.
 Every tile has a floating-point heat value which diffuses to its neighbours.
-Add a heat map view which can be toggled or cycled to.
+
+### Heat overlay
+
+A heat map view can be toggled or cycled to.
 It is possible to cycle the view using a UI element.
+Tile colours are displayed as a value along a gradient from cold to hot tiles.
 
 ## Tile Health
 

half-earth/nodes/game.tscn

@@ -1,4 +1,4 @@
-[gd_scene load_steps=11 format=2]
+[gd_scene load_steps=13 format=2]
 
 [ext_resource path="res://nodes/grid.tscn" type="PackedScene" id=1]
 [ext_resource path="res://nodes/grid_cursor.tscn" type="PackedScene" id=2]
@@ -7,8 +7,10 @@
 [ext_resource path="res://nodes/interaction_modes/interaction_mode.tscn" type="PackedScene" id=5]
 [ext_resource path="res://nodes/ui/build_mode_ui.tscn" type="PackedScene" id=6]
 [ext_resource path="res://nodes/interaction_modes/build_mode.tscn" type="PackedScene" id=7]
-[ext_resource path="res://resources/tile_types/wild.tres" type="Resource" id=8]
+[ext_resource path="res://nodes/ui/overlays UI.tscn" type="PackedScene" id=8]
 [ext_resource path="res://nodes/ui/mode_selection_ui.tscn" type="PackedScene" id=9]
+[ext_resource path="res://nodes/overlays.tscn" type="PackedScene" id=10]
+[ext_resource path="res://resources/overlays/overlays.tres" type="Resource" id=11]
 
 [sub_resource type="Curve" id=1]
 _data = [ Vector2( 0, 0 ), 0.0, 5.0, 0, 0, Vector2( 0.5, 1 ), 0.0, 0.0, 0, 0, Vector2( 1, 0 ), -4.0, 0.0, 0, 0 ]
@@ -18,21 +20,24 @@ _data = [ Vector2( 0, 0 ), 0.0, 5.0, 0, 0, Vector2( 0.5, 1 ), 0.0, 0.0, 0, 0, Ve
 [node name="Clock" parent="." instance=ExtResource( 4 )]
 _autoTick = true
 
-[node name="Grid" parent="." instance=ExtResource( 1 )]
+[node name="World Grid" parent="." instance=ExtResource( 1 )]
 DiffusionCoefficient = 0.1
-_startTileTypeResource = ExtResource( 8 )
 
 [node name="Cursor" parent="." instance=ExtResource( 2 )]
-Grid = NodePath("../Grid")
+Grid = NodePath("../World Grid")
 _pulseShape = SubResource( 1 )
 
 [node name="Interaction Modes" parent="." instance=ExtResource( 5 )]
 _buildModePath = NodePath("Build Mode")
 
 [node name="Build Mode" parent="Interaction Modes" instance=ExtResource( 7 )]
-_gridPath = NodePath("../../Grid")
+_gridPath = NodePath("../../World Grid")
 _cursorPath = NodePath("../../Cursor")
 
+[node name="Overlays" parent="." instance=ExtResource( 10 )]
+_overlaysResource = ExtResource( 11 )
+_worldGridPath = NodePath("../World Grid")
+
 [node name="UI" type="Control" parent="."]
 anchor_right = 1.0
 anchor_bottom = 1.0
@@ -45,15 +50,19 @@ _buildModePath = NodePath("../../Interaction Modes/Build Mode")
 
 [node name="Mode Selection" parent="UI" instance=ExtResource( 9 )]
 
+[node name="Overlays UI" parent="UI" instance=ExtResource( 8 )]
+_overlaysPath = NodePath("../../Overlays")
+
 [connection signal="OnPauseChanged" from="Clock" to="UI/Debug" method="_on_Clock_OnPauseChanged"]
-[connection signal="OnTick" from="Clock" to="Grid" method="_on_Clock_OnTick"]
+[connection signal="OnTick" from="Clock" to="World Grid" method="_on_Clock_OnTick"]
 [connection signal="OnTick" from="Clock" to="UI/Debug" method="_on_Clock_OnTick"]
 [connection signal="OnInteractionModeChanged" from="Interaction Modes" to="Cursor" method="_on_Interaction_Mode_OnInteractionModeChanged"]
 [connection signal="OnInteractionModeChanged" from="Interaction Modes" to="UI/Debug" method="_on_Interaction_Mode_OnInteractionModeChanged"]
 [connection signal="OnModeEntered" from="Interaction Modes/Build Mode" to="Interaction Modes" method="_on_Build_Mode_OnModeEntered"]
 [connection signal="OnModeEntered" from="Interaction Modes/Build Mode" to="UI/Mode Selection" method="EnableBuildMode"]
 [connection signal="OnModeExited" from="Interaction Modes/Build Mode" to="Interaction Modes" method="_on_Build_Mode_OnModeExited"]
+[connection signal="OnModeExited" from="Interaction Modes/Build Mode" to="UI/Mode Selection" method="Enable"]
 [connection signal="SelectedTileTypeChanged" from="Interaction Modes/Build Mode" to="UI/Build Mode" method="UpdateButtonToggleState"]
+[connection signal="OverlayCycled" from="Overlays" to="UI/Overlays UI" method="UpdateOverlayText"]
 [connection signal="OnExit" from="UI/Build Mode" to="Interaction Modes" method="Reset"]
-[connection signal="OnExit" from="UI/Build Mode" to="UI/Mode Selection" method="Enable"]
 [connection signal="BuildModeEnabled" from="UI/Mode Selection" to="Interaction Modes/Build Mode" method="Enable"]

half-earth/nodes/grid.tscn

@@ -1,10 +1,11 @@
-[gd_scene load_steps=3 format=2]
+[gd_scene load_steps=4 format=2]
 
 [ext_resource path="res://scripts/WorldGrid.cs" type="Script" id=1]
 [ext_resource path="res://nodes/tile.tscn" type="PackedScene" id=2]
+[ext_resource path="res://resources/tiles/tiles.tres" type="Resource" id=3]
 
 [node name="Grid" type="Node2D"]
 script = ExtResource( 1 )
 TileScene = ExtResource( 2 )
-Size = 10
 CellSize = 64
+_tileGridResource = ExtResource( 3 )

half-earth/nodes/interaction_modes/build_mode.tscn

@@ -1,7 +1,7 @@
 [gd_scene load_steps=3 format=2]
 
 [ext_resource path="res://scripts/interaction_modes/BuildMode.cs" type="Script" id=1]
-[ext_resource path="res://resources/tile_types/tile_type_collections/buildable_tiles.tres" type="Resource" id=2]
+[ext_resource path="res://resources/tiles/tile_types/tile_type_collections/buildable_tiles.tres" type="Resource" id=2]
 
 [node name="Build Mode" type="Node"]
 script = ExtResource( 1 )

half-earth/nodes/overlays.tscn

@@ -0,0 +1,12 @@
+[gd_scene load_steps=5 format=2]
+
+[ext_resource path="res://scripts/overlays/Overlays.cs" type="Script" id=1]
+[ext_resource path="res://resources/overlays/heat_overlay.tres" type="Resource" id=2]
+[ext_resource path="res://resources/overlays/no_overlay.tres" type="Resource" id=3]
+[ext_resource path="res://resources/tiles/tiles.tres" type="Resource" id=4]
+
+[node name="Overlays" type="Node"]
+script = ExtResource( 1 )
+_cycleOverlayKey = 16777218
+_overlayResources = [ ExtResource( 3 ), ExtResource( 2 ) ]
+_tileGridResource = ExtResource( 4 )

half-earth/nodes/ui/mode_selection_ui.tscn

@@ -14,6 +14,6 @@ margin_left = 2.0
 margin_top = 562.0
 margin_right = 38.0
 margin_bottom = 598.0
-text = "Build Mode"
+text = "[B] Build Mode"
 
 [connection signal="pressed" from="Build Mode" to="." method="EnableBuildMode"]

half-earth/nodes/ui/overlays UI.tscn

@@ -0,0 +1,18 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://scripts/ui/OverlaysUI.cs" type="Script" id=1]
+
+[node name="Overlays UI" type="Node"]
+script = ExtResource( 1 )
+_cycleOverlayButtonPath = NodePath("Button")
+
+[node name="Button" type="Button" parent="."]
+anchor_top = 1.0
+anchor_bottom = 1.0
+margin_top = -90.0
+margin_right = 42.0
+margin_bottom = -52.0
+grow_vertical = 0
+text = "[Tab] Cycle Overlay"
+
+[connection signal="pressed" from="Button" to="." method="CycleOverlay"]

half-earth/resources/overlays/heat_overlay.tres

@@ -0,0 +1,8 @@
+[gd_resource type="Resource" load_steps=2 format=2]
+
+[ext_resource path="res://scripts/overlays/HeatOverlay.cs" type="Script" id=1]
+
+[resource]
+script = ExtResource( 1 )
+_coldColor = Color( 0, 0, 0, 1 )
+_hotColor = Color( 1, 0.654902, 0, 1 )

half-earth/resources/overlays/no_overlay.tres

@@ -0,0 +1,8 @@
+[gd_resource type="Resource" load_steps=2 format=2]
+
+[ext_resource path="res://scripts/overlays/NoOverlay.cs" type="Script" id=1]
+
+[resource]
+script = ExtResource( 1 )
+_healthy = Color( 0.0431373, 0.541176, 0.0235294, 1 )
+_depleted = Color( 0.670588, 0.572549, 0.27451, 1 )

half-earth/resources/overlays/overlays.tres

@@ -0,0 +1,9 @@
+[gd_resource type="Resource" load_steps=4 format=2]
+
+[ext_resource path="res://scripts/overlays/OverlayCollection.cs" type="Script" id=1]
+[ext_resource path="res://resources/overlays/no_overlay.tres" type="Resource" id=2]
+[ext_resource path="res://resources/overlays/heat_overlay.tres" type="Resource" id=3]
+
+[resource]
+script = ExtResource( 1 )
+_resources = [ ExtResource( 2 ), ExtResource( 3 ) ]

half-earth/resources/tile_types/tile_type_collections/buildable_tiles.tres

@@ -1,8 +0,0 @@
-[gd_resource type="Resource" load_steps=3 format=2]
-
-[ext_resource path="res://scripts/TileTypeCollection.cs" type="Script" id=1]
-[ext_resource path="res://resources/tile_types/developed.tres" type="Resource" id=2]
-
-[resource]
-script = ExtResource( 1 )
-_tileTypeResources = [ ExtResource( 2 ) ]

half-earth/resources/tile_types/wild.tres

@@ -1,10 +0,0 @@
-[gd_resource type="Resource" load_steps=2 format=2]
-
-[ext_resource path="res://scripts/TileType.cs" type="Script" id=1]
-
-[resource]
-script = ExtResource( 1 )
-Name = "Wild"
-BuildLabel = "[W]ild"
-Key = 87
-Color = Color( 0, 0.545098, 0.0196078, 1 )

half-earth/resources/tiles/tile_types/developed.tres

@@ -1,10 +1,10 @@
 [gd_resource type="Resource" load_steps=2 format=2]
 
-[ext_resource path="res://scripts/TileType.cs" type="Script" id=1]
+[ext_resource path="res://scripts/tile/TileType.cs" type="Script" id=1]
 
 [resource]
 script = ExtResource( 1 )
 Name = "Developed"
-BuildLabel = "[D]eveloped"
 Key = 68
 Color = Color( 0.372549, 0.372549, 0.372549, 1 )
+HeatGeneration = 0.15

half-earth/resources/tiles/tile_types/tile_type_collections/buildable_tiles.tres

@@ -0,0 +1,8 @@
+[gd_resource type="Resource" load_steps=3 format=2]
+
+[ext_resource path="res://scripts/tile/TileTypeCollection.cs" type="Script" id=1]
+[ext_resource path="res://resources/tiles/tile_types/developed.tres" type="Resource" id=2]
+
+[resource]
+script = ExtResource( 1 )
+_resources = [ ExtResource( 2 ) ]

half-earth/resources/tiles/tile_types/wild.tres

@@ -0,0 +1,11 @@
+[gd_resource type="Resource" load_steps=2 format=2]
+
+[ext_resource path="res://scripts/tile/Wild.cs" type="Script" id=1]
+
+[resource]
+script = ExtResource( 1 )
+Name = "Wild"
+Key = 87
+Color = Color( 0.14902, 1, 0, 0 )
+HeatGeneration = -0.02
+Threshold = 0.6

half-earth/resources/tiles/tiles.tres

@@ -0,0 +1,9 @@
+[gd_resource type="Resource" load_steps=3 format=2]
+
+[ext_resource path="res://scripts/tile/TileGrid.cs" type="Script" id=1]
+[ext_resource path="res://resources/tiles/tile_types/wild.tres" type="Resource" id=2]
+
+[resource]
+script = ExtResource( 1 )
+Size = 10
+_startTileTypeResource = ExtResource( 2 )

half-earth/scripts/HeatSystem.cs

@@ -0,0 +1,100 @@
+using Godot;
+
+public class HeatSystem
+{
+    private readonly TileGrid _tiles;
+    private readonly float _diffusionCoefficient;
+
+    private float[] _nextTemperatures = null;
+
+    public HeatSystem(TileGrid tiles, float diffusionCoefficient)
+    {
+        _tiles = tiles;
+        _diffusionCoefficient = diffusionCoefficient;
+        _nextTemperatures = new float[tiles.Count];
+    }
+
+    public void Process()
+    {
+        GenerateHeat();
+        Diffuse();
+    }
+
+
+    private float TransferHeat(float t0, float alpha, float nx, float ny, float px, float py)
+    {
+        float d2tdx2 = nx - 2 * t0 + px;
+        float d2tdy2 = ny - 2 * t0 + py;
+        return t0 + alpha * (d2tdx2 + d2tdy2);
+    }
+
+    private void GetNeighbourTemperatures(int x, int y, out float nx, out float ny, out float px, out float py)
+    {
+        // default value
+        var t = _tiles[x, y].temperature;
+
+        nx = x > 0 ? _tiles[x - 1, y].temperature : t;
+        px = x < _tiles.Size - 1 ? _tiles[x + 1, y].temperature : t;
+
+        ny = y > 0 ? _tiles[x, y - 1].temperature : t;
+        py = y < _tiles.Size - 1 ? _tiles[x, y + 1].temperature : t;
+    }
+    private void GenerateHeat()
+    {
+        for (int i = 0; i < _tiles.Count; i++)
+        {
+            var tile = _tiles[i];
+            var type = tile.type;
+            tile.temperature += type.HeatGeneration;
+            ApplyHeatDamage(ref tile);
+            _tiles[i] = tile;
+        }
+    }
+
+    private void ApplyHeatDamage(ref Tile tile)
+    {
+        if (!(tile.type is IDamageable damageable))
+            return;
+
+        var surplus = tile.temperature - damageable.Threshold;
+        if (surplus < 0)
+            return;
+
+        // TODO: parameterised balancing
+        tile.currentHealth -= surplus;
+        tile.currentHealth = Mathf.Clamp(tile.currentHealth, 0, 1);
+    }
+
+    private void Diffuse()
+    {
+        var D = _diffusionCoefficient;
+
+        for (int i = 0; i < _tiles.Count; i++)
+        {
+            float t = _tiles[i].temperature;
+
+            _tiles.MapIndex(i, out var x, out var y);
+
+            GetNeighbourTemperatures(
+                x, y,
+                out var nx,
+                out var ny,
+                out var px,
+                out var py);
+
+            var temperature = TransferHeat(t, D, nx, ny, px, py);
+
+            // TODO: what if it's really really cold out?
+            temperature = Mathf.Max(0, temperature);
+            _nextTemperatures[i] = temperature;
+        }
+
+        for (int i = 0; i < _tiles.Count; i++)
+        {
+            var tile = _tiles[i];
+            tile.temperature = _nextTemperatures[i];
+            _tiles[i] = tile;
+        }
+    }
+
+}

half-earth/scripts/ReadOnlyResourceList.cs

@@ -0,0 +1,33 @@
+using Godot;
+using System.Collections;
+using System.Collections.Generic;
+
+public abstract class ReadOnlyResourceList<T> : Resource, IReadOnlyList<T> where T : Resource
+{
+    [Export]
+    private List<Resource> _resources = new List<Resource>();
+    private List<T> Collection
+    {
+        get
+        {
+            if (_collection != null)
+                return _collection;
+
+            _collection = new List<T>();
+            foreach (var resource in _resources)
+            {
+                _collection.Add((T)resource);
+            }
+            return _collection;
+        }
+    }
+    private List<T> _collection = null;
+
+    public T this[int index] => Collection[index];
+
+    public int Count => Collection.Count;
+
+    public IEnumerator<T> GetEnumerator() => Collection.GetEnumerator();
+
+    IEnumerator IEnumerable.GetEnumerator() => Collection.GetEnumerator();
+}

half-earth/scripts/TileTypeCollection.cs

@@ -1,46 +0,0 @@
-using Godot;
-using System;
-using System.Collections;
-using System.Collections.Generic;
-
-public class TileTypeCollection : Resource, IReadOnlyList<TileType>
-{
-    [Export]
-    private List<Resource> _tileTypeResources = new List<Resource>();
-
-    private List<TileType> TileTypes
-    {
-        get
-        {
-            if (_tileTypes != null)
-                return _tileTypes;
-
-            _tileTypes = new List<TileType>();
-
-            foreach (var resource in _tileTypeResources)
-            {
-                if (!(resource is TileType))
-                    throw new InvalidCastException($"{resource} must be a {typeof(TileType)}");
-
-                _tileTypes.Add((TileType)resource);
-            }
-
-            return _tileTypes;
-        }
-    }
-    private List<TileType> _tileTypes = null;
-
-    public TileType this[int index] => TileTypes[index];
-
-    public int Count => TileTypes.Count;
-
-    public IEnumerator<TileType> GetEnumerator()
-    {
-        return TileTypes.GetEnumerator();
-    }
-
-    IEnumerator IEnumerable.GetEnumerator()
-    {
-        return TileTypes.GetEnumerator();
-    }
-}

half-earth/scripts/WorldGrid.cs

@@ -7,11 +7,8 @@ public class WorldGrid : Node2D
     private PackedScene TileScene { get; set; }
 
     [Export]
-    private Resource _startTileTypeResource;
-    private TileType _startTileType;
-
-    [Export]
-    public int Size { get; set; }
+    private Resource _tileGridResource;
+    private TileGrid _tileGrid;
 
     [Export]
     public int CellSize { get; set; }
@@ -19,65 +16,49 @@ public class WorldGrid : Node2D
     [Export]
     public float DiffusionCoefficient { get; set; } = 0.01f;
 
-    private Tile[,] _tiles;
-    private float[,] _nextValues = null;
+    public struct TileView
+    {
+        public ShaderMaterial material;
+    }
+    private TileView[] _tileViews;
+    private HeatSystem _heat;
 
     // Called when the node enters the scene tree for the first time.
     public override void _Ready()
     {
-        _startTileType = (TileType)_startTileTypeResource;
+        _tileGrid = (TileGrid)_tileGridResource;
 
-        GenerateGrid(Size);
-    }
-
-    public override void _Process(float delta)
-    {
-        base._Process(delta);
-
-        for (int x = 0; x < Size; x++)
-        {
-            for (int y = 0; y < Size; y++)
-            {
-                var tile = _tiles[x, y];
-                var material = tile.material;
-                material.SetShaderParam("t", tile.value);
-            }
-        }
-    }
-
-    public bool IsInBounds(int x, int y)
-    {
-        return x >= 0 && x < Size && y >= 0 && y < Size;
-    }
-
-    public void ToggleTileHighlight(int x, int y)
-    {
-        if (!IsInBounds(x, y))
-            return;
-
-        _tiles[x, y].isHighlighted ^= true;
-    }
-
-    public void SetTileType(int x, int y, TileType tileType)
-    {
-        if (!IsInBounds(x, y))
-            return;
-
-        GD.Print($"set ({x}, {y}) to {tileType}");
-        _tiles[x, y].type = tileType;
-        _tiles[x, y].material.SetShaderParam("lowColor", tileType.Color);
+        GenerateCanvasItems(_tileGrid);
+
+        _heat = new HeatSystem(_tileGrid, DiffusionCoefficient);
     }
 
+    #region Positioning
     public void GetGridPos(Vector2 position, out int x, out int y)
     {
         x = Mathf.FloorToInt(position.x / CellSize);
         y = Mathf.FloorToInt(position.y / CellSize);
     }
 
+    public bool IsInBounds(int x, int y) => _tileGrid.IsInBounds(x, y);
+    #endregion
+
+    #region Interaction
+    public void SetTileType(int x, int y, TileType tileType)
+    {
+        if (!_tileGrid.IsInBounds(x, y))
+            return;
+
+        _tileGrid.MapPosition(x, y, out var idx);
+
+        var tile = _tileGrid[idx];
+        tile.type = tileType;
+        _tileGrid[x, y] = tile;
+    }
+    #endregion
+
     private void Clear()
     {
-        _tiles = null;
-
         int children = this.GetChildCount();
         GD.Print(children);
         for (int i = 0; i < children; i++)
@@ -85,92 +66,39 @@ public class WorldGrid : Node2D
             var child = this.GetChild(i);
             child.QueueFree();
         }
+
+        _tileViews = null;
     }
 
-    private void GenerateGrid(int size)
+    private void GenerateCanvasItems(TileGrid grid)
     {
         this.Clear();
 
-        _tiles = new Tile[size, size];
-        _nextValues = new float[size, size];
+        _tileViews = new TileView[grid.Count];
 
-        for (int x = 0; x < size; x++)
+        for (int i = 0; i < grid.Count; i++)
         {
-            for (int y = 0; y < size; y++)
+            _tileGrid.MapIndex(i, out var x, out var y);
+
+            var node = TileScene.Instance<Node2D>();
+            this.AddChild(node);
+            var position = new Vector2
             {
-                var tile = new Tile();
-                tile.isHighlighted = false;
-                tile.value = 0.0f;
-                tile.type = _startTileType;
+                x = (x + .5f) * CellSize,
+                y = (y + .5f) * CellSize
+            };
+            node.Position = position;
+            var canvasItem = (CanvasItem)node;
 
-                var node = TileScene.Instance<Node2D>();
-                this.AddChild(node);
-                var position = new Vector2
-                {
-                    x = (x + .5f) * CellSize,
-                    y = (y + .5f) * CellSize
-                };
-                node.Position = position;
-                var canvasItem = (CanvasItem)node;
-                tile.material = (ShaderMaterial)canvasItem.Material;
-                tile.material.SetShaderParam("lowColor", _startTileType.Color);
+            var tile = _tileGrid[i];
 
-                _tiles[x, y] = tile;
-            }
+            TileView view = default;
+            view.material = (ShaderMaterial)canvasItem.Material;
+            _tileViews[i] = view;
         }
     }
 
-    public void _on_Clock_OnTick(int ticks)
-    {
-        Diffuse();
-    }
+    public ShaderMaterial GetTileMaterial(int idx) => _tileViews[idx].material;
 
-    private float TransferHeat(float t0, float alpha, float nx, float ny, float px, float py)
-    {
-        float d2tdx2 = nx - 2 * t0 + px;
-        float d2tdy2 = ny - 2 * t0 + py;
-        return t0 + alpha * (d2tdx2 + d2tdy2);
-    }
-
-    private void GetNeighbourTemperatures(int x, int y, out float nx, out float ny, out float px, out float py)
-    {
-        // default value
-        var t = _tiles[x, y].value;
-
-        nx = x > 0 ? _tiles[x - 1, y].value : t;
-        px = x < Size - 1 ? _tiles[x + 1, y].value : t;
-
-        ny = y > 0 ? _tiles[x, y - 1].value : t;
-        py = y < Size - 1 ? _tiles[x, y + 1].value : t;
-    }
-
-    private void Diffuse()
-    {
-        for (int x = 0; x < Size; x++)
-        {
-            for (int y = 0; y < Size; y++)
-            {
-                float t = _tiles[x, y].value;
-                var D = DiffusionCoefficient;
-
-                GetNeighbourTemperatures(
-                    x, y,
-                    out var nx,
-                    out var ny,
-                    out var px,
-                    out var py);
-
-                // current value
-                _nextValues[x, y] = TransferHeat(t, D, nx, ny, px, py);
-            }
-        }
-
-        for (int x = 0; x < Size; x++)
-        {
-            for (int y = 0; y < Size; y++)
-            {
-                _tiles[x, y].value = _nextValues[x, y];
-            }
-        }
-    }
+    public void _on_Clock_OnTick(int ticks) => _heat.Process();
 }

half-earth/scripts/overlays/HeatOverlay.cs

@@ -0,0 +1,18 @@
+using Godot;
+using System;
+
+public class HeatOverlay : Overlay
+{
+    [Export]
+    private Color _coldColor;
+
+    [Export]
+    private Color _hotColor;
+
+    public override void Apply(Tile tile, ShaderMaterial material)
+    {
+        material.SetShaderParam("lowColor", _coldColor);
+        material.SetShaderParam("highColor", _hotColor);
+        material.SetShaderParam("t", tile.temperature);
+    }
+}

half-earth/scripts/overlays/NoOverlay.cs

@@ -0,0 +1,27 @@
+using Godot;
+
+public class NoOverlay : Overlay
+{
+    [Export]
+    private Color _healthy;
+
+    [Export]
+    private Color _depleted;
+
+    // in this view we want to draw tiles with their normal colour
+    public override void Apply(Tile tile, ShaderMaterial material)
+    {
+        var type = tile.type;
+
+        if (type is Wild wild)
+        {
+            material.SetShaderParam("lowColor", _depleted);
+            material.SetShaderParam("highColor", _healthy);
+            material.SetShaderParam("t", tile.currentHealth);
+            return;
+        }
+
+        material.SetShaderParam("lowColor", type.Color);
+        material.SetShaderParam("t", 0);
+    }
+}

half-earth/scripts/overlays/Overlay.cs

@@ -0,0 +1,7 @@
+using Godot;
+
+public abstract class Overlay : Resource
+{
+    public string Name => GetType().ToString();
+    public abstract void Apply(Tile tile, ShaderMaterial material);
+}

half-earth/scripts/overlays/OverlayCollection.cs

@@ -0,0 +1,3 @@
+public class OverlayCollection : ReadOnlyResourceList<Overlay>
+{
+}

half-earth/scripts/overlays/Overlays.cs

@@ -0,0 +1,67 @@
+using Godot;
+using System;
+
+public class Overlays : Node
+{
+    [Signal]
+    delegate void OverlayCycled(Overlay overlay);
+
+    [Export]
+    private KeyList _cycleOverlayKey;
+
+    [Export] private Resource _overlaysResource;
+    public Overlay Current => _overlays[_overlayIdx];
+    private OverlayCollection _overlays;
+    private int _overlayIdx = 0;
+
+    [Export]
+    private Resource _tileGridResource;
+    private TileGrid _tileGrid;
+
+    [Export]
+    private NodePath _worldGridPath;
+    private WorldGrid _worldGrid;
+
+    public override void _Ready()
+    {
+        _overlays = (OverlayCollection)_overlaysResource;
+        _tileGrid = (TileGrid)_tileGridResource;
+        _worldGrid = GetNode<WorldGrid>(_worldGridPath);
+    }
+
+    public override void _Input(InputEvent @event)
+    {
+        base._Input(@event);
+
+        if (!(@event is InputEventKey keyEvent))
+            return;
+
+        if (!(keyEvent.Pressed))
+            return;
+
+        if ((KeyList)keyEvent.Scancode != _cycleOverlayKey)
+            return;
+
+        CycleOverlay();
+    }
+
+    public override void _Process(float delta)
+    {
+        base._Process(delta);
+
+        for (int i = 0; i < _tileGrid.Count; i++)
+        {
+            var tile = _tileGrid[i];
+            var material = _worldGrid.GetTileMaterial(i);
+
+            Current.Apply(tile, material);
+        }
+    }
+
+    public void CycleOverlay()
+    {
+        _overlayIdx++;
+        _overlayIdx %= _overlays.Count;
+        EmitSignal(nameof(OverlayCycled), Current);
+    }
+}

half-earth/scripts/tile/IDamageable.cs

@@ -0,0 +1,4 @@
+public interface IDamageable
+{
+    float Threshold { get; }
+}

half-earth/scripts/tile/Tile.cs

@@ -3,7 +3,7 @@ using Godot;
 public struct Tile
 {
     public bool isHighlighted;
-    public float value;
-    public ShaderMaterial material;
+    public float temperature;
     public TileType type;
+    public float currentHealth;
 }

half-earth/scripts/tile/TileGrid.cs

@@ -0,0 +1,93 @@
+using Godot;
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+public class TileGrid : Resource, IReadOnlyList<Tile>
+{
+    [Export]
+    public int Size { get; private set; } = 10;
+
+    [Export]
+    private Resource _startTileTypeResource;
+    private TileType StartTileType => (TileType)_startTileTypeResource;
+
+    public int Count => Size * Size;
+
+    public Tile this[int index]
+    {
+        get => Tiles[index];
+        set => Tiles[index] = value;
+    }
+
+    public Tile this[int x, int y]
+    {
+        get
+        {
+            MapPosition(x, y, out int idx);
+            return Tiles[idx];
+        }
+        set
+        {
+            MapPosition(x, y, out int idx);
+            Tiles[idx] = value;
+        }
+    }
+
+    private List<Tile> Tiles
+    {
+        get
+        {
+            if (_tiles == null)
+            {
+                _tiles = new List<Tile>();
+                Generate(_tiles);
+            }
+
+            return _tiles;
+        }
+    }
+    private List<Tile> _tiles = null;
+
+    private void Generate(List<Tile> tiles)
+    {
+        tiles.Clear();
+        for (int i = 0; i < Count; i++)
+        {
+            var tile = new Tile();
+            tile.isHighlighted = false;
+            tile.temperature = 0.0f;
+            tile.type = StartTileType;
+            tile.currentHealth = 1.0f;
+
+            tiles.Add(tile);
+        }
+    }
+
+    public IEnumerator<Tile> GetEnumerator()
+    {
+        return Tiles.GetEnumerator();
+    }
+
+    IEnumerator IEnumerable.GetEnumerator()
+    {
+        return Tiles.GetEnumerator();
+    }
+
+    public void MapIndex(int idx, out int x, out int y)
+    {
+        y = idx / Size;
+        x = idx % Size;
+    }
+
+    public void MapPosition(int x, int y, out int idx)
+    {
+        idx = y * Size + x;
+    }
+
+    public bool IsInBounds(int x, int y)
+    {
+        return x >= 0 && x < Size && y >= 0 && y < Size;
+    }
+}
+

half-earth/scripts/tile/TileType.cs

@@ -5,8 +5,7 @@ public class TileType : Resource
     [Export]
     public string Name { get; private set; }
 
-    [Export]
-    public string BuildLabel { get; private set; }
+    public string BuildLabel => $"[{Key}] {Name}";
 
     [Export]
     public KeyList Key { get; private set; }
@@ -14,8 +13,8 @@ public class TileType : Resource
     [Export]
     public Color Color { get; private set; }
 
-    public override string ToString()
-    {
-        return Name;
-    }
+    [Export]
+    public float HeatGeneration { get; private set; }
+
+    public override string ToString() => Name;
 }

half-earth/scripts/tile/TileTypeCollection.cs

@@ -0,0 +1,3 @@
+public class TileTypeCollection : ReadOnlyResourceList<TileType>
+{
+}

half-earth/scripts/tile/Wild.cs

@@ -0,0 +1,7 @@
+using Godot;
+
+public class Wild : TileType, IDamageable
+{
+    [Export]
+    public float Threshold { get; private set; }
+}

half-earth/scripts/ui/OverlaysUI.cs

@@ -0,0 +1,36 @@
+using Godot;
+using System;
+using System.Collections.Generic;
+
+public class OverlaysUI : Node
+{
+    [Export]
+    private NodePath _cycleOverlayButtonPath;
+    private Button _cycleOverlayButton;
+
+    [Export]
+    private NodePath _overlaysPath;
+    private Overlays _overlays;
+
+    private string _mainText;
+
+    public override void _Ready()
+    {
+        base._Ready();
+
+        _cycleOverlayButton = GetNode<Button>(_cycleOverlayButtonPath);
+        _mainText = _cycleOverlayButton.Text;
+
+        _overlays = GetNode<Overlays>(_overlaysPath);
+    }
+
+    public void CycleOverlay()
+    {
+        _overlays.CycleOverlay();
+    }
+
+    public void UpdateOverlayText(Overlay overlay)
+    {
+        _cycleOverlayButton.Text = $"{_mainText} ({_overlays.Current.Name})";
+    }
+}