engine: add deterministic glyph mask core

2026-07-30 18:25:46 -04:00
parent 41001f6f77
commit 7397e4e5fb
9 changed files with 818 additions and 8 deletions
--- a/engine/Age.Engine/Text/AgeGlyphMaskCompositor.cs
+++ b/engine/Age.Engine/Text/AgeGlyphMaskCompositor.cs
@@ -0,0 +1,135 @@
+using Age.Engine.Model;
+using Age.Engine.Sys4;
+
+namespace Age.Engine.Text;
+
+/// <summary>AGE's deterministic 32-bit glyph-mask compositor, independent of mask provenance.</summary>
+public static class AgeGlyphMaskCompositor
+{
+    public static void DrawGlyph(
+        RgbaImage destination,
+        GlyphMask mask,
+        int cellX,
+        int cellY,
+        int topToBaseline,
+        AdvTextStyle style)
+    {
+        ArgumentNullException.ThrowIfNull(destination);
+        ArgumentNullException.ThrowIfNull(mask);
+        ValidateDestination(destination);
+        int baselineY = checked(cellY + topToBaseline);
+
+        if (style.RenderMode == 1)
+            DrawMask(destination, mask,
+                checked(cellX + style.EffectOffsetX),
+                checked(baselineY + style.EffectOffsetY),
+                style.EffectColor);
+        else if (style.RenderMode == 3)
+            foreach ((int x, int y) in GetMode3OutlineOffsets(
+                         style.EffectOffsetX, style.EffectOffsetY))
+                DrawMask(destination, mask, checked(cellX + x), checked(baselineY + y),
+                         style.EffectColor);
+
+        DrawMask(destination, mask, cellX, baselineY, style.TextColor);
+        if (style.RenderMode == 2)
+            DrawMask(destination, mask, cellX, baselineY, style.TextColor, coverageShift: 2);
+    }
+
+    /// <summary>
+    /// Draw at a GDI-style baseline. mask.OriginX moves right from the pen and mask.OriginY moves
+    /// upward from the baseline. coverageShift=2 reproduces AGE's mode-2 quarter-coverage pass.
+    /// </summary>
+    public static bool DrawMask(
+        RgbaImage destination,
+        GlyphMask mask,
+        int baselineX,
+        int baselineY,
+        long rgb,
+        int coverageShift = 0)
+    {
+        ArgumentNullException.ThrowIfNull(destination);
+        ArgumentNullException.ThrowIfNull(mask);
+        ValidateDestination(destination);
+        if (coverageShift is < 0 or > 4)
+            throw new ArgumentOutOfRangeException(nameof(coverageShift));
+
+        int red = (int)((rgb >> 16) & 0xff);
+        int green = (int)((rgb >> 8) & 0xff);
+        int blue = (int)(rgb & 0xff);
+        int left = checked(baselineX + mask.OriginX);
+        int top = checked(baselineY - mask.OriginY);
+        ReadOnlySpan<byte> coverage = mask.Coverage.Span;
+        bool changed = false;
+
+        for (int row = 0; row < mask.Height; row++)
+        {
+            int y = checked(top + row);
+            if ((uint)y >= (uint)destination.Height) continue;
+            int sourceRow = row * mask.Stride;
+            for (int column = 0; column < mask.Width; column++)
+            {
+                int x = checked(left + column);
+                if ((uint)x >= (uint)destination.Width) continue;
+                int level = coverage[sourceRow + column] >> coverageShift;
+                if (level == 0) continue;
+                int alpha = level * 255 / 16;
+                BlendTextPixel(destination.Pixels,
+                    checked((y * destination.Width + x) * 4),
+                    red, green, blue, alpha);
+                changed = true;
+            }
+        }
+        return changed;
+    }
+
+    public static IReadOnlyList<(int X, int Y)> GetMode3OutlineOffsets(int radiusX, int radiusY)
+    {
+        double radius = Math.Sqrt((double)radiusX * radiusX + (double)radiusY * radiusY);
+        if (radius == 0) return Array.Empty<(int, int)>();
+        int sampleCount = checked((int)Math.Ceiling(radius * 8.0));
+        var result = new (int X, int Y)[sampleCount];
+        double step = 360.0 / (radius * 8.0);
+        for (int index = 0; index < result.Length; index++)
+        {
+            double radians = index * step * Math.PI / 180.0;
+            result[index] = (
+                RoundNearest(Math.Cos(radians) * radiusX),
+                RoundNearest(Math.Sin(radians) * radiusY));
+        }
+        return result;
+    }
+
+    private static int RoundNearest(double value)
+        => checked((int)(value < 0 ? value - 0.5 : value + 0.5));
+
+    private static void BlendTextPixel(
+        byte[] destination, int offset, int red, int green, int blue, int alpha)
+    {
+        int destinationAlpha = destination[offset + 3];
+        if (alpha == 255 || destinationAlpha == 0)
+        {
+            destination[offset] = (byte)red;
+            destination[offset + 1] = (byte)green;
+            destination[offset + 2] = (byte)blue;
+            destination[offset + 3] = (byte)alpha;
+            return;
+        }
+
+        int inverse = 255 - alpha;
+        destination[offset] =
+            (byte)((destination[offset] * inverse + red * alpha) / 255);
+        destination[offset + 1] =
+            (byte)((destination[offset + 1] * inverse + green * alpha) / 255);
+        destination[offset + 2] =
+            (byte)((destination[offset + 2] * inverse + blue * alpha) / 255);
+        destination[offset + 3] = (byte)Math.Max(destinationAlpha, alpha);
+    }
+
+    private static void ValidateDestination(RgbaImage destination)
+    {
+        if (destination.Width <= 0 || destination.Height <= 0
+            || destination.Pixels.Length != checked(destination.Width * destination.Height * 4))
+            throw new ArgumentException("Destination must be a non-empty tightly packed RGBA image.",
+                                        nameof(destination));
+    }
+}