Improve vertical font handling

Author: BobLd

UglyToad.PdfPig.Rendering.Skia.Tests/Documents/DefaultColourSpaces.230802.pdf

@@ -23,7 +23,8 @@ public class PageSizeTests
 {
     private static readonly HashSet<string> _documentsToIgnore =
     [
-        "Type3Test.pdf" // fails in 0.1.15
+        "Type3Test.pdf", // fails in 0.1.15
+        "DefaultColourSpaces.230802.pdf", // fails in 0.1.15
     ];
 
     public static IEnumerable<object[]> GetAllDocuments => Directory.EnumerateFiles(Helper.DocumentsFolder, "*.pdf")

UglyToad.PdfPig.Rendering.Skia.Tests/Documents/VerticalText.pdf

@@ -796,8 +796,13 @@ public class TestRendering
             "TextClippingModeChanges_1.png",
             "TextClippingModeChanges.pdf", 1, 2
         },
+        new object[]
+        {
+            "VerticalText_1.png",
+            "VerticalText.pdf", 1, 2
+        },
 
-        // TODO - Add Type3Test.pdf test
+        // TODO - Add Type3Test.pdf + DefaultColourSpaces.230802.pdf test
     };
 
     [Theory]

UglyToad.PdfPig.Rendering.Skia.Tests/ExpectedImages/linux/pdfpig_skia/VerticalText_1.png

@@ -28,7 +28,8 @@ public class VisualTests
     [
         "SPARC - v9 Architecture Manual.pdf",
         "TIKA-1552-0.pdf",
-        "Type3Test.pdf" // fails in 0.1.15
+        "Type3Test.pdf", // fails in 0.1.15
+        "DefaultColourSpaces.230802.pdf", // fails in 0.1.15
     ];
 
     public static IEnumerable<object[]> GetAllDocuments => Directory.EnumerateFiles(Helper.DocumentsFolder, "*.pdf")

UglyToad.PdfPig.Rendering.Skia.Tests/ExpectedImages/macos/pdfpig_skia/VerticalText_1.png

@@ -15,6 +15,7 @@
 using System;
 using System.Runtime.CompilerServices;
 using SkiaSharp;
+using SkiaSharp.HarfBuzz;
 using UglyToad.PdfPig.Core;
 using UglyToad.PdfPig.Graphics.Colors;
 using UglyToad.PdfPig.Graphics.Core;
@@ -28,6 +29,79 @@ internal static class SkiaExtensions
 
         private static readonly string DefaultFamilyName = SKTypeface.Default.FamilyName;
 
+        /// <summary>
+        /// Draw a shaped glyph run for the fallback (non-vector) text path. Horizontal text uses the
+        /// default shaper; vertical text is shaped top-to-bottom (see <see cref="ShapeVertical"/>) so
+        /// HarfBuzz substitutes the vertical presentation forms.
+        /// </summary>
+        public static void DrawShapedText(this SKCanvas canvas, SKShaper shaper, string text, SKFont skFont, SKPaint paint, bool vertical)
+        {
+            if (!vertical)
+            {
+                canvas.DrawShapedText(shaper, text, SKPoint.Empty, SKTextAlign.Left, skFont, paint);
+                return;
+            }
+
+            // See https://github.com/mono/SkiaSharp/issues/4273
+            var shaped = shaper.ShapeVertical(text, skFont);
+
+            using var builder = new SKTextBlobBuilder();
+            var run = builder.AllocateRawPositionedRun(skFont, shaped.Codepoints.Length);
+            var glyphs = run.Glyphs;
+            var positions = run.Positions;
+            for (int i = 0; i < shaped.Codepoints.Length; ++i)
+            {
+                glyphs[i] = (ushort)shaped.Codepoints[i];
+                positions[i] = shaped.Points[i];
+            }
+
+            using var blob = builder.Build();
+            if (blob is not null)
+            {
+                canvas.DrawText(blob, 0, 0, paint);
+            }
+            else
+            {
+                // Fallback to default
+                canvas.DrawShapedText(shaper, text, SKPoint.Empty, SKTextAlign.Left, skFont, paint);
+            }
+        }
+
+        /// <summary>
+        /// Shape <paramref name="text"/> for vertical writing mode, returning the vertical
+        /// presentation-form glyphs positioned with the horizontal layout.
+        /// <para>
+        /// Setting the buffer direction top-to-bottom makes HarfBuzz apply its default 'vert' feature,
+        /// substituting the vertical presentation forms (rotated brackets, repositioned punctuation, the
+        /// prolonged-sound mark, ...). We take only the substituted glyph ids from that pass and keep the
+        /// <em>horizontal</em> glyph positions: PdfPig already places the pen for vertical writing using
+        /// the font's position vector (W2/DW2), so HarfBuzz's vertical positions — which add the fallback
+        /// font's own vertical-origin offset on top — would shift every glyph off its bounding box. For
+        /// the single glyph PdfPig renders per character code the horizontal position is simply the origin.
+        /// </para>
+        /// </summary>
+        public static SKShaper.Result ShapeVertical(this SKShaper shaper, string text, SKFont skFont)
+        {
+            // See https://github.com/mono/SkiaSharp/issues/4273
+            using var buffer = new HarfBuzzSharp.Buffer();
+            buffer.AddUtf16(text);
+            buffer.GuessSegmentProperties();
+            buffer.Direction = HarfBuzzSharp.Direction.TopToBottom;
+            SKShaper.Result vertical = shaper.Shape(buffer, skFont);
+
+            SKShaper.Result horizontal = shaper.Shape(text, skFont);
+
+            // 'vert' is a one-to-one (GSUB single) substitution, so the horizontal and vertical passes
+            // produce the same glyph count in the same order. When that holds, draw the vertical glyphs
+            // at the horizontal positions; otherwise fall back to the vertical result unchanged.
+            if (horizontal.Codepoints.Length == vertical.Codepoints.Length)
+            {
+                return new SKShaper.Result(vertical.Codepoints, vertical.Clusters, horizontal.Points, horizontal.Width);
+            }
+
+            return vertical;
+        }
+
         public static bool IsDefault(this SKTypeface typeface)
         {
             return typeface.FamilyName.Equals(DefaultFamilyName);

UglyToad.PdfPig.Rendering.Skia.Tests/ExpectedImages/pdfpig_skia/VerticalText_1.png

@@ -222,7 +222,7 @@ private void ShowNonVectorFontGlyph(IFont font, IColor? strokingColor, IColor? n
             // canvas matrix so cm/q/Q changes later in the same text object don't shift it.
             if (textRenderingMode.IsClip())
             {
-                using var glyphPath = GetPath(drawTypeface, renderUnicode);
+                using var glyphPath = GetPath(drawTypeface, renderUnicode, font.IsVertical);
                 if (!glyphPath.IsEmpty)
                 {
                     AppendGlyphToTextClipPath(glyphPath);
@@ -257,7 +257,7 @@ private void ShowNonVectorFontGlyph(IFont font, IColor? strokingColor, IColor? n
                         throw new ArgumentNullException($"Expecting a {nameof(PatternColor)} but got '{nonStrokingColor.GetType()}'.");
                     }
 
-                    using (var path = GetPath(drawTypeface, renderUnicode))
+                    using (var path = GetPath(drawTypeface, renderUnicode, font.IsVertical))
                     {
                         ShowVectorFontGlyph(path, strokingColor, nonStrokingColor,
                             textRenderingMode, in TransformationMatrix.Identity, in TransformationMatrix.Identity);
@@ -270,7 +270,7 @@ private void ShowNonVectorFontGlyph(IFont font, IColor? strokingColor, IColor? n
                     DrawWithSoftMask(softMask!, currentState.BlendMode, () =>
                     {
                         using var skFont = drawTypeface.Typeface.ToFont(1f);
-                        _canvas.DrawShapedText(drawTypeface.Shaper, renderUnicode, SKPoint.Empty, SKTextAlign.Left, skFont, innerPaint);
+                        _canvas.DrawShapedText(drawTypeface.Shaper, renderUnicode, skFont, innerPaint, font.IsVertical);
                     });
                 }
                 else
@@ -280,7 +280,7 @@ private void ShowNonVectorFontGlyph(IFont font, IColor? strokingColor, IColor? n
 
                     using (var skFont = drawTypeface.Typeface.ToFont(1f))
                     {
-                        _canvas.DrawShapedText(drawTypeface.Shaper, renderUnicode, SKPoint.Empty, SKTextAlign.Left, skFont, fillPaint);
+                        _canvas.DrawShapedText(drawTypeface.Shaper, renderUnicode, skFont, fillPaint, font.IsVertical);
                     }
                 }
             }
@@ -310,7 +310,7 @@ private void ShowNonVectorFontGlyph(IFont font, IColor? strokingColor, IColor? n
                     DrawWithSoftMask(softMask!, currentState.BlendMode, () =>
                     {
                         using var skFont = drawTypeface.Typeface.ToFont(1f);
-                        _canvas.DrawShapedText(drawTypeface.Shaper, renderUnicode, SKPoint.Empty, SKTextAlign.Left, skFont, innerStrokePaint);
+                        _canvas.DrawShapedText(drawTypeface.Shaper, renderUnicode, skFont, innerStrokePaint, font.IsVertical);
                     });
                 }
                 else
@@ -321,7 +321,7 @@ private void ShowNonVectorFontGlyph(IFont font, IColor? strokingColor, IColor? n
 
                     using (var skFont = drawTypeface.Typeface.ToFont(1f))
                     {
-                        _canvas.DrawShapedText(drawTypeface.Shaper, renderUnicode, SKPoint.Empty, SKTextAlign.Left, skFont, strokePaint);
+                        _canvas.DrawShapedText(drawTypeface.Shaper, renderUnicode, skFont, strokePaint, font.IsVertical);
                     }
                 }
             }
@@ -501,11 +501,13 @@ private static SKRect GetType3GlyphBoundingBox(IReadOnlyList<IGraphicsStateOpera
             return SKRect.Create(-1000, -1000, 2000, 2000);
         }
 
-        private static SKPath GetPath(SkiaFontCacheItem fontItem, string unicode)
+        private static SKPath GetPath(SkiaFontCacheItem fontItem, string unicode, bool vertical)
         {
             using (var skFont = fontItem.Typeface.ToFont(1f))
             {
-                var shaped = fontItem.Shaper.Shape(unicode, skFont);
+                var shaped = vertical
+                    ? fontItem.Shaper.ShapeVertical(unicode, skFont)
+                    : fontItem.Shaper.Shape(unicode, skFont);
 
                 var combinedPath = new SKPath();
                 for (int i = 0; i < shaped.Codepoints.Length; ++i)
@@ -520,7 +522,7 @@ private static SKPath GetPath(SkiaFontCacheItem fontItem, string unicode)
                         combinedPath.AddPath(glyphPath, in matrix);
                     }
                 }
-
+                
                 return combinedPath;
             }
         }