feat(ui): D.2b-B — UiMeter vertical fill (burden bar, retail m_eDirection 2/4)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/UI/UiMeter.cs

@@ -55,6 +55,14 @@ public sealed class UiMeter : UiElement
     /// <summary>Coloured-fill right-cap RenderSurface id.</summary>
     public uint FrontRight { get; set; }
 
+    /// <summary>Vertical orientation (retail <c>m_eDirection</c> 2/4). Default false =
+    /// horizontal (direction 1). The burden bar is the only vertical meter today.</summary>
+    public bool Vertical { get; set; }
+
+    /// <summary>For a vertical meter, fill grows from the bottom up (retail direction 4)
+    /// when true, top-down (direction 2) when false. Default bottom-up. Visual-confirmed.</summary>
+    public bool FillFromBottom { get; set; } = true;
+
     public UiMeter() { ClickThrough = true; }
 
     /// <summary>The meter draws its own 3-slice bars; the importer must not build its
@@ -71,6 +79,18 @@ public sealed class UiMeter : UiElement
         return (0f, 0f, w * pct, h);
     }
 
+    /// <summary>Clamp <paramref name="pct"/> to [0,1] and return the vertical fill rect
+    /// (local px). <paramref name="fromBottom"/> true → the fill occupies the bottom
+    /// <c>h*pct</c> px (retail direction 4); false → the top (direction 2).</summary>
+    public static (float x, float y, float w, float h) ComputeVFillRect(
+        float pct, float w, float h, bool fromBottom)
+    {
+        if (pct < 0f) pct = 0f;
+        if (pct > 1f) pct = 1f;
+        float fh = h * pct;
+        return (0f, fromBottom ? h - fh : 0f, w, fh);
+    }
+
     protected override void OnDraw(UiRenderContext ctx)
     {
         float? pct = Fill();
@@ -78,14 +98,25 @@ public sealed class UiMeter : UiElement
 
         if (SpriteResolve is { } resolve && (BackLeft != 0 || BackTile != 0 || FrontTile != 0))
         {
-            // Retail meter (UIElement_Meter::DrawChildren): the BACK 3-slice is the
+            if (Vertical)
-            // empty track, drawn full width; the FRONT 3-slice is the coloured fill,
+            {
-            // drawn at FULL width too but horizontally CLIPPED to the fill fraction.
+                // Track full height, fill clipped to the fraction along the fill direction.
-            // The front carries its own right-cap (shown at 100%); clipping below 100%
+                // The burden meter is a single-tile bar (BackTile/FrontTile, no caps).
-            // removes it and reveals the back track's right-cap — retail's scissor-fill.
+                DrawVBar(ctx, resolve, BackTile, Height, fromBottom: FillFromBottom, isFill: false);
-            DrawHBar(ctx, resolve, BackLeft, BackTile, BackRight, Width);
+                if (pct is not null && p > 0f)
-            if (pct is not null && p > 0f)
+                    DrawVBar(ctx, resolve, FrontTile, Height * p, fromBottom: FillFromBottom, isFill: true);
-                DrawHBar(ctx, resolve, FrontLeft, FrontTile, FrontRight, Width * p);
+            }
+            else
+            {
+                // Retail meter (UIElement_Meter::DrawChildren): the BACK 3-slice is the
+                // empty track, drawn full width; the FRONT 3-slice is the coloured fill,
+                // drawn at FULL width too but horizontally CLIPPED to the fill fraction.
+                // The front carries its own right-cap (shown at 100%); clipping below 100%
+                // removes it and reveals the back track's right-cap — retail's scissor-fill.
+                DrawHBar(ctx, resolve, BackLeft, BackTile, BackRight, Width);
+                if (pct is not null && p > 0f)
+                    DrawHBar(ctx, resolve, FrontLeft, FrontTile, FrontRight, Width * p);
+            }
         }
         else
         {
@@ -158,6 +189,28 @@ public sealed class UiMeter : UiElement
         DrawPiece(ctx, rt, w - capR, capR, rw, h, clipW);
     }
 
+    /// <summary>Draws a single-tile vertical bar slice. The track (<paramref name="isFill"/>
+    /// false) spans the full height; the fill spans <paramref name="visibleH"/> px from the
+    /// bottom (<paramref name="fromBottom"/>) or top, UV-cropped to that fraction of the
+    /// sprite so the fill reveals the matching part of the art (retail
+    /// UIElement_Meter::DrawChildren Box2D clip, direction 2/4). A 0 id is a no-op.</summary>
+    private void DrawVBar(UiRenderContext ctx, Func<uint, (uint tex, int w, int h)> resolve,
+        uint tileId, float visibleH, bool fromBottom, bool isFill)
+    {
+        if (tileId == 0 || visibleH <= 0f) return;
+        var (tex, _, _) = resolve(tileId);
+        if (tex == 0) return;
+        float w = Width, h = Height;
+        if (visibleH > h) visibleH = h;
+        float frac = h > 0f ? visibleH / h : 0f;
+        // Bottom-up fill: bottom of the rect AND bottom of the sprite (v in [1-frac, 1]).
+        // Top-down / track: top of the rect AND top of the sprite (v in [0, frac]).
+        float y  = isFill && fromBottom ? h - visibleH : 0f;
+        float v0 = isFill && fromBottom ? 1f - frac : 0f;
+        float v1 = isFill && fromBottom ? 1f : frac;
+        ctx.DrawSprite(tex, 0f, y, w, visibleH, 0f, v0, 1f, v1, System.Numerics.Vector4.One);
+    }
+
     /// <summary>Draw a slice over local [<paramref name="pieceX"/>,
     /// pieceX+<paramref name="pieceW"/>], with the texture repeating every
     /// <paramref name="nativeW"/> px (UV-repeat — the UI texture is GL_REPEAT-wrapped).

tests/AcDream.App.Tests/UI/UiMeterVerticalTests.cs

@@ -0,0 +1,35 @@
+using AcDream.App.UI;
+using Xunit;
+
+namespace AcDream.App.Tests.UI;
+
+public class UiMeterVerticalTests
+{
+    [Fact]
+    public void Vertical_fill_from_bottom_occupies_lower_fraction()
+    {
+        // 11x58 bar, 50% → fill rect is the bottom 29px.
+        var (x, y, w, h) = UiMeter.ComputeVFillRect(0.5f, 11f, 58f, fromBottom: true);
+        Assert.Equal(0f, x);
+        Assert.Equal(29f, y, 3);    // h - h*p = 58 - 29
+        Assert.Equal(11f, w);
+        Assert.Equal(29f, h, 3);
+    }
+
+    [Fact]
+    public void Vertical_fill_from_top_starts_at_zero()
+    {
+        var (_, y, _, h) = UiMeter.ComputeVFillRect(0.25f, 11f, 58f, fromBottom: false);
+        Assert.Equal(0f, y);
+        Assert.Equal(14.5f, h, 3);
+    }
+
+    [Theory]
+    [InlineData(-1f, 0f)]
+    [InlineData(2f, 58f)]
+    public void Vertical_fill_clamps_fraction(float pct, float expectedH)
+    {
+        var (_, _, _, h) = UiMeter.ComputeVFillRect(pct, 11f, 58f, fromBottom: true);
+        Assert.Equal(expectedH, h, 3);
+    }
+}