Auto-scale the UI based on dpi and resolution - Closes #643

Code is taken from Godot's editor, so I assume it should work well.

src/Main.gd

@@ -14,6 +14,7 @@ onready var right_cursor: Sprite = $RightCursor
 
 
 func _init() -> void:
+	Global.shrink = _get_auto_display_scale()
 	if OS.get_name() == "OSX":
 		_use_osx_shortcuts()
 
@@ -88,6 +89,22 @@ func _input(event: InputEvent) -> void:
 			get_focus_owner().release_focus()
 
 
+# Taken from https://github.com/godotengine/godot/blob/3.x/editor/editor_settings.cpp#L1474
+func _get_auto_display_scale() -> float:
+	if OS.get_name() == "OSX":
+		return OS.get_screen_max_scale()
+
+	var dpi := OS.get_screen_dpi()
+	var smallest_dimension: int = min(OS.get_screen_size().x, OS.get_screen_size().y)
+	if dpi >= 192 && smallest_dimension >= 1400:
+		return 2.0  # hiDPI display.
+	elif smallest_dimension >= 1700:
+		return 1.5  # Likely a hiDPI display, but we aren't certain due to the returned DPI.
+	elif smallest_dimension <= 800:
+		return 0.75  # Small loDPI display.
+	return 1.0
+
+
 func _setup_application_window_size() -> void:
 	get_tree().set_screen_stretch(
 		SceneTree.STRETCH_MODE_DISABLED,

src/Preferences/PreferencesDialog.gd

@@ -90,6 +90,7 @@ onready var right_side: VBoxContainer = $HSplitContainer/ScrollContainer/VBoxCon
 onready var autosave_container: Container = right_side.get_node("Backup/AutosaveContainer")
 onready var autosave_interval: SpinBox = autosave_container.get_node("AutosaveInterval")
 onready var shrink_label: Label = right_side.get_node("Interface/ShrinkContainer/ShrinkLabel")
+onready var shrink_h_slider: HSlider = $"%ShrinkHSlider"
 onready var themes: BoxContainer = right_side.get_node("Interface/Themes")
 onready var shortcuts: Control = right_side.get_node("Shortcuts")
 onready var extensions: BoxContainer = right_side.get_node("Extensions")
@@ -111,6 +112,7 @@ class Preference:
 func _ready() -> void:
 	# Replace OK since preference changes are being applied immediately, not after OK confirmation
 	get_ok().text = tr("Close")
+	shrink_h_slider.value = Global.shrink  # In case shrink is not equal to 1
 
 	for child in shortcuts.get_children():
 		if not child is AcceptDialog:

src/Preferences/PreferencesDialog.tscn

@@ -154,6 +154,7 @@ text = "1"
 align = 2
 
 [node name="ShrinkHSlider" type="HSlider" parent="HSplitContainer/ScrollContainer/VBoxContainer/Interface/ShrinkContainer"]
+unique_name_in_owner = true
 margin_left = 142.0
 margin_right = 446.0
 margin_bottom = 16.0