feat(ui): port retained widget foundations

src/AcDream.App/UI/UiButtonStateMachine.cs

@@ -0,0 +1,79 @@
+namespace AcDream.App.UI;
+
+/// <summary>Inputs to retail <c>UIElement_Button::UpdateState_</c>.</summary>
+public readonly record struct UiButtonVisualInput(
+    bool Disabled,
+    bool Selected,
+    bool RolloverEnabled,
+    bool Pressed,
+    bool PointerOver);
+
+/// <summary>
+/// GL-free retail button visual-state policy. State ids are the numeric
+/// <c>UIStateId</c> values from the DAT.
+/// </summary>
+public static class UiButtonStateMachine
+{
+    public const uint Normal = 1u;
+    public const uint NormalRollover = 2u;
+    public const uint NormalPressed = 3u;
+    public const uint Highlight = 6u;
+    public const uint HighlightRollover = 7u;
+    public const uint HighlightPressed = 8u;
+    public const uint Ghosted = 13u;
+
+    public static uint RequestedState(UiButtonVisualInput input)
+    {
+        if (input.Disabled)
+            return Ghosted;
+
+        uint requested = input.Selected ? Highlight : Normal;
+        if (input.Pressed || (input.RolloverEnabled && input.PointerOver))
+            requested = input.Selected ? HighlightRollover : NormalRollover;
+        if (input.Pressed && input.PointerOver)
+            requested = input.Selected ? HighlightPressed : NormalPressed;
+        return requested;
+    }
+
+    /// <summary>
+    /// Returns the requested state when it exists; otherwise returns the current
+    /// state unchanged. Retail does not search for a nearest fallback.
+    /// </summary>
+    public static uint ResolveState(
+        uint currentState,
+        UiButtonVisualInput input,
+        IReadOnlySet<uint> availableStates)
+    {
+        uint requested = RequestedState(input);
+        return availableStates.Contains(requested) ? requested : currentState;
+    }
+
+    public static string StateName(uint stateId)
+        => stateId switch
+        {
+            Normal => "Normal",
+            NormalRollover => "Normal_rollover",
+            NormalPressed => "Normal_pressed",
+            Highlight => "Highlight",
+            HighlightRollover => "Highlight_rollover",
+            HighlightPressed => "Highlight_pressed",
+            Ghosted => "Ghosted",
+            _ => "",
+        };
+
+    public static bool TryStateId(string stateName, out uint stateId)
+    {
+        stateId = stateName switch
+        {
+            "Normal" => Normal,
+            "Normal_rollover" => NormalRollover,
+            "Normal_pressed" => NormalPressed,
+            "Highlight" => Highlight,
+            "Highlight_rollover" => HighlightRollover,
+            "Highlight_pressed" => HighlightPressed,
+            "Ghosted" => Ghosted,
+            _ => 0u,
+        };
+        return stateId != 0;
+    }
+}