add selection mode ui #5

gdd.md

@@ -8,6 +8,19 @@
 * Education
 * Supply chains
 
+## Interaction Modes
+
+Interaction modes can be changed via keyboard shortcut.
+
+### Selection Mode
+
+This is the default interaction mode.
+It can be accessed at any time by pressing the `esc` key.
+
+### Build Mode
+
+Build mode can be entered by pressing the `b` key.
+
 ## Critical Path
 
 ### Grid
@@ -28,6 +41,27 @@ Add a tick counter as a UI element.
 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
+
+Diffusion is modelled as two-dimensional steady-state heat conduction.
+This means that the amount of a value does not change between the start and end of the computation of the diffusion step.
+The value at one 2D location is calculated based on the values of itself and its neighbours in the previous step.
+A diffusion coefficient controls the rate of diffusion.
+
+[Video explanation](https://www.youtube.com/watch?v=RGbV7T_iWT8)
+[Derivation](https://www.tec-science.com/thermodynamics/heat/heat-equation-diffusion-equation/)
+
+Implementation:
+
+```cs
+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);
+}
+```
+
 ### Tile Types
 
 Tiles start as wild tiles.

half-earth/materials/cursor.tres

@@ -4,6 +4,6 @@
 
 [resource]
 shader = ExtResource( 1 )
-shader_param/baseColor = Color( 0.992157, 1, 0, 1 )
+shader_param/lowColor = Color( 0, 0, 0, 0 )
-shader_param/highlightColor = Color( 1, 0, 0.984314, 1 )
+shader_param/highColor = Color( 0, 0.976471, 1, 1 )
-shader_param/isHighlighted = 0
+shader_param/t = null

half-earth/materials/tile.tres

@@ -5,6 +5,6 @@
 [resource]
 resource_local_to_scene = true
 shader = ExtResource( 1 )
-shader_param/baseColor = Color( 0.0823529, 0, 1, 1 )
+shader_param/lowColor = Color( 0, 0, 0, 1 )
-shader_param/highlightColor = Color( 1, 0, 0, 1 )
+shader_param/highColor = Color( 1, 0.560784, 0, 1 )
-shader_param/isHighlighted = null
+shader_param/t = null

half-earth/nodes/clock.tscn

@@ -0,0 +1,7 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://scripts/Clock.cs" type="Script" id=1]
+
+[node name="Clock" type="Node"]
+script = ExtResource( 1 )
+_tickRate = 10.0

half-earth/nodes/game.tscn

@@ -1,11 +1,61 @@
-[gd_scene load_steps=3 format=2]
+[gd_scene load_steps=11 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]
+[ext_resource path="res://nodes/ui/debug_ui.tscn" type="PackedScene" id=3]
+[ext_resource path="res://nodes/clock.tscn" type="PackedScene" id=4]
+[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://nodes/interaction_modes/selection_mode.tscn" type="PackedScene" id=8]
+[ext_resource path="res://nodes/ui/selection_mode_ui.tscn" type="PackedScene" id=9]
 
-[node name="Root" type="Node2D"]
+[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 ]
+
+[node name="Root" type="Node"]
+
+[node name="Clock" parent="." instance=ExtResource( 4 )]
+_autoTick = true
 
 [node name="Grid" parent="." instance=ExtResource( 1 )]
+DiffusionCoefficient = 0.1
 
 [node name="Cursor" parent="." instance=ExtResource( 2 )]
 Grid = NodePath("../Grid")
+_pulseShape = SubResource( 1 )
+
+[node name="Interaction Mode" parent="." instance=ExtResource( 5 )]
+_buildModePath = NodePath("../Build Mode")
+_selectionModePath = NodePath("../Selection Mode")
+
+[node name="Build Mode" parent="." instance=ExtResource( 7 )]
+_key = 66
+
+[node name="Selection Mode" parent="." instance=ExtResource( 8 )]
+
+[node name="UI" type="Control" parent="."]
+anchor_right = 1.0
+anchor_bottom = 1.0
+mouse_filter = 2
+
+[node name="Debug" parent="UI" instance=ExtResource( 3 )]
+
+[node name="Build Mode" parent="UI" instance=ExtResource( 6 )]
+visible = false
+_buildModePath = NodePath("../../Build Mode")
+
+[node name="Selection Mode" parent="UI" instance=ExtResource( 9 )]
+_selectionModePath = NodePath("../../Selection Mode")
+
+[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="UI/Debug" method="_on_Clock_OnTick"]
+[connection signal="OnInteractionModeChanged" from="Interaction Mode" to="Cursor" method="_on_Interaction_Mode_OnInteractionModeChanged"]
+[connection signal="OnInteractionModeChanged" from="Interaction Mode" to="UI/Debug" method="_on_Interaction_Mode_OnInteractionModeChanged"]
+[connection signal="OnModeEntered" from="Build Mode" to="Interaction Mode" method="_on_Build_Mode_OnModeEntered"]
+[connection signal="OnModeExited" from="Build Mode" to="Interaction Mode" method="_on_Build_Mode_OnModeExited"]
+[connection signal="OnModeEntered" from="Selection Mode" to="Interaction Mode" method="_on_Selection_Mode_OnModeEntered"]
+[connection signal="OnModeExited" from="Selection Mode" to="Interaction Mode" method="_on_Selection_Mode_OnModeExited"]
+[connection signal="OnExit" from="UI/Build Mode" to="Interaction Mode" method="Reset"]
+[connection signal="EnableBuildMode" from="UI/Selection Mode" to="Build Mode" method="Enable"]

half-earth/nodes/interaction_modes/build_mode.tscn

@@ -0,0 +1,6 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://scripts/interaction_modes/BuildMode.cs" type="Script" id=1]
+
+[node name="Build Mode" type="Node"]
+script = ExtResource( 1 )

half-earth/nodes/interaction_modes/interaction_mode.tscn

@@ -0,0 +1,6 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://scripts/interaction_modes/InteractionModes.cs" type="Script" id=1]
+
+[node name="Interaction Mode" type="Node"]
+script = ExtResource( 1 )

half-earth/nodes/interaction_modes/selection_mode.tscn

@@ -0,0 +1,7 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://scripts/interaction_modes/SelectionMode.cs" type="Script" id=1]
+
+[node name="Selection Mode" type="Node"]
+script = ExtResource( 1 )
+_key = 16777217

half-earth/nodes/ui/build_mode_ui.tscn

@@ -0,0 +1,26 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://scripts/ui/BuildModeUI.cs" type="Script" id=1]
+
+[node name="Build Mode" type="Control"]
+anchor_top = 1.0
+anchor_bottom = 1.0
+margin_top = -600.0
+margin_bottom = -600.0
+script = ExtResource( 1 )
+
+[node name="Exit" type="Button" parent="."]
+margin_left = 2.0
+margin_top = 562.0
+margin_right = 38.0
+margin_bottom = 598.0
+text = "Exit"
+
+[node name="Developed" type="Button" parent="."]
+margin_left = 54.0
+margin_top = 562.0
+margin_right = 90.0
+margin_bottom = 598.0
+text = "Developed"
+
+[connection signal="pressed" from="Exit" to="." method="_on_Exit_pressed"]

half-earth/nodes/ui/debug_ui.tscn

@@ -0,0 +1,48 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://scripts/ui/DebugUI.cs" type="Script" id=1]
+
+[node name="Debug UI" type="Control"]
+anchor_left = 1.0
+anchor_right = 1.0
+mouse_filter = 2
+script = ExtResource( 1 )
+TicksLabelPath = NodePath("Ticks")
+PauseLabelPath = NodePath("Paused")
+InteractionModeLabelPath = NodePath("Interaction Mode")
+
+[node name="Interaction Mode" type="Label" parent="."]
+anchor_left = 1.0
+anchor_right = 1.0
+margin_left = -102.0
+margin_top = 15.0
+margin_right = -14.0
+margin_bottom = 29.0
+grow_horizontal = 0
+grow_vertical = 0
+text = "mode: Selection"
+align = 2
+
+[node name="Ticks" type="Label" parent="."]
+anchor_left = 1.0
+anchor_right = 1.0
+margin_left = -60.0
+margin_top = 35.0
+margin_right = -14.0
+margin_bottom = 49.0
+grow_horizontal = 0
+grow_vertical = 0
+text = "ticks: 0"
+align = 2
+
+[node name="Paused" type="Label" parent="."]
+anchor_left = 1.0
+anchor_right = 1.0
+margin_left = -90.0
+margin_top = 55.0
+margin_right = -14.0
+margin_bottom = 69.0
+grow_horizontal = 0
+grow_vertical = 0
+text = "pause: false"
+align = 2

half-earth/nodes/ui/selection_mode_ui.tscn

@@ -0,0 +1,19 @@
+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://scripts/ui/SelectionModeUI.cs" type="Script" id=1]
+
+[node name="Selection Mode UI" type="Control"]
+anchor_top = 1.0
+anchor_bottom = 1.0
+margin_top = -600.0
+margin_bottom = -600.0
+script = ExtResource( 1 )
+
+[node name="Build Mode" type="Button" parent="."]
+margin_left = 2.0
+margin_top = 562.0
+margin_right = 38.0
+margin_bottom = 598.0
+text = "Build Mode"
+
+[connection signal="pressed" from="Build Mode" to="." method="_on_Build_Mode_pressed"]

half-earth/scripts/Clock.cs

@@ -0,0 +1,67 @@
+using Godot;
+using System;
+
+public class Clock : Node
+{
+    [Signal]
+    delegate void OnTick(int ticks);
+    [Signal]
+    delegate void OnPauseChanged(bool paused);
+
+    [Export(PropertyHint.None, "Number of ticks per second")]
+    private float _tickRate;
+    private float TickPeriod => 1.0f / _tickRate;
+
+    [Export]
+    private bool _autoTick;
+
+    private int _ticks = 0;
+    private bool _paused = false;
+
+    public override void _Input(InputEvent @event)
+    {
+        base._Input(@event);
+
+        if (@event is InputEventKey keyEvent && keyEvent.Pressed)
+        {
+            switch ((KeyList)keyEvent.Scancode)
+            {
+                case KeyList.Space:
+                    if (_autoTick)
+                    {
+                        _paused = !_paused;
+                        EmitSignal(nameof(OnPauseChanged), _paused);
+                        return;
+                    }
+                    Tick();
+                    break;
+            }
+        }
+    }
+
+    private float _secondsSinceLastTick;
+
+    public override void _Process(float delta)
+    {
+        base._Process(delta);
+
+        if (!_autoTick)
+            return;
+
+        if (_paused)
+            return;
+
+        _secondsSinceLastTick += delta;
+        if (_secondsSinceLastTick < TickPeriod)
+            return;
+
+        _secondsSinceLastTick -= TickPeriod;
+        Tick();
+    }
+
+    private void Tick()
+    {
+        _ticks++;
+        EmitSignal(nameof(OnTick), _ticks);
+    }
+}

half-earth/scripts/GridCursor.cs

@@ -8,7 +8,18 @@ public class GridCursor : Sprite
     private WorldGrid _grid;
     private ShaderMaterial _material;
 
-    private const string IS_HIGHLIGHTED = "isHighlighted";
+    #region Animation
+    [Export]
+    private Curve _pulseShape;
+    [Export]
+    private float _pulseRate = 1.0f;
+    private float PulsePeriod => 1.0f / _pulseRate;
+    #endregion
+
+    private float _elapsed = 0.0f;
+    private bool _pulsing = false;
+
+    private const string T = "t";
 
     public override void _Ready()
     {
@@ -27,25 +38,44 @@ public class GridCursor : Sprite
             this.Visible = _grid.IsInBounds(x, y);
             var position = new Vector2(x + .5f, y + .5f) * _grid.CellSize;
             this.Position = position;
+            return;
         }
-        else if (@event is InputEventMouseButton mouseButtonEvent)
+
+        if (@event is InputEventMouseButton mouseButtonEvent)
         {
-            switch ((ButtonList)mouseButtonEvent.ButtonIndex)
+            var button = (ButtonList)mouseButtonEvent.ButtonIndex;
+            if (button != ButtonList.Left)
+                return;
+
+            if (!mouseButtonEvent.Pressed)
             {
-                case ButtonList.Left:
+                _material.SetShaderParam(T, 0f);
-                    if (mouseButtonEvent.Pressed)
+                return;
-                    {
-                        var pos = mouseButtonEvent.Position;
-                        _grid.GetGridPos(pos, out var x, out var y);
-                        _grid.ToggleTileHighlight(x, y);
-                        _material.SetShaderParam(IS_HIGHLIGHTED, 1);
-                    }
-                    else
-                    {
-                        _material.SetShaderParam(IS_HIGHLIGHTED, 0);
-                    }
-                    break;
             }
+
+            var pos = mouseButtonEvent.Position;
+            _grid.GetGridPos(pos, out var x, out var y);
+            _grid.SetTileValue(x, y, 1.0f);
+            _material.SetShaderParam(T, 1f);
         }
     }
+
+    public override void _Process(float delta)
+    {
+        _elapsed += delta * _pulseRate;
+
+        if (!_pulsing)
+        {
+            _material.SetShaderParam(T, 1f);
+            return;
+        }
+
+        var a = _pulseShape.Interpolate(_elapsed % 1.0f);
+        _material.SetShaderParam(T, a);
+    }
+
+    public void _on_Interaction_Mode_OnInteractionModeChanged(Mode oldMode, Mode newMode)
+    {
+        _pulsing = newMode is BuildMode;
+    }
 }

half-earth/scripts/Tile.cs

@@ -0,0 +1,8 @@
+using Godot;
+
+public struct Tile
+{
+    public bool isHighlighted;
+    public float value;
+    public ShaderMaterial material;
+}

half-earth/scripts/WorldGrid.cs

@@ -12,12 +12,11 @@ public class WorldGrid : Node2D
     [Export]
     public int CellSize { get; set; }
 
-    private struct Tile
+    [Export]
-    {
+    public float DiffusionCoefficient { get; set; } = 0.01f;
-        public bool isHighlighted;
+
-        public ShaderMaterial material;
-    }
     private Tile[,] _tiles;
+    private float[,] _nextValues = null;
 
     // Called when the node enters the scene tree for the first time.
     public override void _Ready()
@@ -35,7 +34,7 @@ public class WorldGrid : Node2D
             {
                 var tile = _tiles[x, y];
                 var material = tile.material;
-                material.SetShaderParam("isHighlighted", tile.isHighlighted ? 1 : 0);
+                material.SetShaderParam("t", tile.value);
             }
         }
     }
@@ -53,6 +52,14 @@ public class WorldGrid : Node2D
         _tiles[x, y].isHighlighted ^= true;
     }
 
+    public void SetTileValue(int x, int y, float value)
+    {
+        if (!IsInBounds(x, y))
+            return;
+
+        _tiles[x, y].value = value;
+    }
+
     public void GetGridPos(Vector2 position, out int x, out int y)
     {
         x = Mathf.FloorToInt(position.x / CellSize);
@@ -77,6 +84,7 @@ public class WorldGrid : Node2D
         this.Clear();
 
         _tiles = new Tile[size, size];
+        _nextValues = new float[size, size];
 
         for (int x = 0; x < size; x++)
         {
@@ -84,6 +92,7 @@ public class WorldGrid : Node2D
             {
                 var tile = new Tile();
                 tile.isHighlighted = false;
+                tile.value = 0.0f;
 
                 var node = TileScene.Instance<Node2D>();
                 this.AddChild(node);
@@ -100,4 +109,58 @@ public class WorldGrid : Node2D
             }
         }
     }
+
+    public void _on_Clock_OnTick(int ticks)
+    {
+        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].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];
+            }
+        }
+    }
 }

half-earth/scripts/interaction_modes/BuildMode.cs

@@ -0,0 +1,9 @@
+using Godot;
+using System;
+
+public class BuildMode : Mode
+{
+    private const int NO_TILE_TYPE_SELECTED = -1;
+
+    public int SelectedTileType { get; set; } = NO_TILE_TYPE_SELECTED;
+}

half-earth/scripts/interaction_modes/InteractionModes.cs

@@ -0,0 +1,75 @@
+using Godot;
+using System;
+
+public class InteractionModes : Node
+{
+    [Export]
+    private NodePath _buildModePath;
+    private BuildMode _buildMode;
+    [Export]
+    private NodePath _selectionModePath;
+    private SelectionMode _selectionMode;
+
+    [Signal]
+    delegate void OnInteractionModeChanged(Mode oldMode, Mode newMode);
+
+    private Mode _current = null;
+
+    public override void _Ready()
+    {
+        base._Ready();
+
+        _selectionMode = GetNode<SelectionMode>(_selectionModePath);
+        _buildMode = GetNode<BuildMode>(_buildModePath);
+    }
+
+    public override void _Process(float delta)
+    {
+        base._Process(delta);
+
+        if (_current == null)
+        {
+            Reset();
+        }
+    }
+
+    public void _on_Build_Mode_OnModeEntered()
+    {
+        _selectionMode.Disable();
+        ChangeMode(_selectionMode, _buildMode);
+    }
+    public void _on_Build_Mode_OnModeExited()
+    {
+    }
+
+    public void _on_Selection_Mode_OnModeEntered()
+    {
+        _buildMode.Disable();
+        ChangeMode(_buildMode, _selectionMode);
+    }
+    public void _on_Selection_Mode_OnModeExited()
+    {
+    }
+
+    private void ChangeMode(Mode oldMode, Mode newMode)
+    {
+        if (oldMode == newMode)
+        {
+            throw new InvalidOperationException();
+        }
+
+        if (_current != null && oldMode != _current)
+        {
+            throw new InvalidOperationException();
+        }
+
+        _current = newMode;
+        EmitSignal(nameof(OnInteractionModeChanged), oldMode, newMode);
+    }
+
+    public void Reset()
+    {
+        _buildMode.Disable();
+        _selectionMode.Enable();
+    }
+}

half-earth/scripts/interaction_modes/Mode.cs

@@ -0,0 +1,63 @@
+using Godot;
+using System;
+
+public abstract class Mode : Node
+{
+    [Signal]
+    delegate void OnModeEntered();
+    [Signal]
+    delegate void OnModeExited();
+
+    [Export]
+    private KeyList _key;
+
+    public bool Active
+    {
+        get => _active;
+        private set
+        {
+            if (value == _active)
+                return;
+
+            _active = value;
+
+            var signal = _active
+                ? nameof(OnModeEntered)
+                : nameof(OnModeExited);
+            EmitSignal(signal);
+        }
+    }
+    private bool _active;
+
+    public override void _Input(InputEvent @event)
+    {
+        base._Input(@event);
+
+        if (!(@event is InputEventKey keyEvent))
+            return;
+
+        if (!keyEvent.Pressed)
+            return;
+
+        var key = (KeyList)keyEvent.Scancode;
+
+        if (key == _key)
+        {
+            Active = true;
+        }
+    }
+
+    public void Enable()
+    {
+        Active = true;
+    }
+    public void Disable()
+    {
+        Active = false;
+    }
+
+    public override string ToString()
+    {
+        return GetType().ToString();
+    }
+}

half-earth/scripts/interaction_modes/SelectionMode.cs

@@ -0,0 +1,6 @@
+using Godot;
+using System;
+
+public class SelectionMode : Mode
+{
+}

half-earth/scripts/ui/BuildModeUI.cs

@@ -0,0 +1,36 @@
+using Godot;
+using System;
+
+public class BuildModeUI : Control
+{
+    [Signal]
+    delegate void OnExit();
+
+    [Export]
+    private NodePath _buildModePath;
+    private BuildMode _buildMode;
+
+    // Called when the node enters the scene tree for the first time.
+    public override void _Ready()
+    {
+        _buildMode = GetNode<BuildMode>(_buildModePath);
+        Visible = false;
+    }
+
+    public void _on_Exit_pressed()
+    {
+        Exit();
+    }
+
+    private void Exit()
+    {
+        EmitSignal(nameof(OnExit));
+    }
+
+    public override void _Process(float delta)
+    {
+        base._Process(delta);
+
+        Visible = _buildMode.Active;
+    }
+}

half-earth/scripts/ui/DebugUI.cs

@@ -0,0 +1,41 @@
+using Godot;
+using System;
+
+public class DebugUI : Control
+{
+    [Export]
+    public NodePath TicksLabelPath { private get; set; }
+    private Label _ticksLabel;
+
+    [Export]
+    public NodePath PauseLabelPath { private get; set; }
+    private Label _pauseLabel;
+
+    [Export]
+    public NodePath InteractionModeLabelPath { private get; set; }
+    private Label _interactionModeLabel;
+    public override void _Ready()
+    {
+        _ticksLabel = GetNode<Label>(TicksLabelPath);
+        _pauseLabel = GetNode<Label>(PauseLabelPath);
+        _interactionModeLabel = GetNode<Label>(InteractionModeLabelPath);
+    }
+
+    #region Signals
+    public void _on_Clock_OnPauseChanged(bool paused) =>
+        SetLabelText(_pauseLabel, "pause", paused);
+
+    public void _on_Clock_OnTick(int ticks) =>
+        SetLabelText(_ticksLabel, "ticks", ticks);
+
+    public void _on_Interaction_Mode_OnInteractionModeChanged(Mode oldMode, Mode newMode)
+    {
+        SetLabelText(_interactionModeLabel, "mode", newMode);
+    }
+    #endregion
+
+    private void SetLabelText(Label label, string key, object value)
+    {
+        label.Text = $"{key}: {value}";
+    }
+}

half-earth/scripts/ui/SelectionModeUI.cs

@@ -0,0 +1,26 @@
+using Godot;
+using System;
+
+public class SelectionModeUI : Control
+{
+    [Signal]
+    delegate void EnableBuildMode();
+
+    [Export]
+    private NodePath _selectionModePath;
+    public SelectionMode _selectionMode;
+
+    public void _on_Build_Mode_pressed() => EmitSignal(nameof(EnableBuildMode));
+
+    public override void _Ready()
+    {
+        _selectionMode = GetNode<SelectionMode>(_selectionModePath);
+    }
+
+    public override void _Process(float delta)
+    {
+        base._Process(delta);
+
+        Visible = _selectionMode.Active;
+    }
+}

half-earth/shaders/tile_shader.gdshader

@@ -1,9 +1,9 @@
 shader_type canvas_item;
 
-uniform vec4 baseColor : hint_color;
+uniform vec4 lowColor : hint_color;
-uniform vec4 highlightColor : hint_color;
+uniform vec4 highColor : hint_color;
-uniform int isHighlighted;
+uniform float t;
 
 void fragment() {
-	COLOR = mix(baseColor, highlightColor, float(isHighlighted));
+	COLOR = mix(lowColor, highColor, t);
 }