QuestPDF/QuestPDF/Drawing/TextShaper.cs

using System;
using System.Linq;
using HarfBuzzSharp;
using QuestPDF.Infrastructure;
using SkiaSharp;
using Buffer = HarfBuzzSharp.Buffer;

namespace QuestPDF.Drawing
{
    internal class TextShaper
    {
        public const int FontShapingScale = 512;
        
        private TextStyle TextStyle { get; }

        private SKFont Font => TextStyle.ToFont();
        private Font ShaperFont => TextStyle.ToShaperFont();
        private SKPaint Paint => TextStyle.ToPaint();

        public TextShaper(TextStyle textStyle)
        {
            TextStyle = textStyle;
        }

        public TextShapingResult Shape(string text)
        {
            using var buffer = new Buffer();
            
            PopulateBufferWithText(buffer, text);
            buffer.GuessSegmentProperties();

            ShaperFont.Shape(buffer);
            
            var length = buffer.Length;
            var glyphInfos = buffer.GlyphInfos;
            var glyphPositions = buffer.GlyphPositions;
            
            var scaleY = Paint.TextSize / FontShapingScale;
            var scaleX = scaleY * Paint.TextScaleX;
            
            var xOffset = 0f;
            var yOffset = 0f;
            
            var glyphs = new ShapedGlyph[length];
            
            for (var i = 0; i < length; i++)
            {
                glyphs[i] = new ShapedGlyph
                {
                    Codepoint = (ushort)glyphInfos[i].Codepoint,
                    Position = new SKPoint(xOffset + glyphPositions[i].XOffset * scaleX, yOffset - glyphPositions[i].YOffset * scaleY),
                    Width = glyphPositions[i].XAdvance * scaleX
                };
                
                xOffset += glyphPositions[i].XAdvance * scaleX;
                yOffset += glyphPositions[i].YAdvance * scaleY;
            }
            
            return new TextShapingResult(glyphs);
        }
        
        void PopulateBufferWithText(Buffer buffer, string text)
        {
            var encoding = Paint.TextEncoding;

            if (encoding == SKTextEncoding.Utf8)
                buffer.AddUtf8(text);
                
            else if (encoding == SKTextEncoding.Utf16)
                buffer.AddUtf16(text);

            else if (encoding == SKTextEncoding.Utf32)
                buffer.AddUtf32(text);

            else
                throw new NotSupportedException("TextEncoding of type GlyphId is not supported.");
        }
    }
    
    internal struct ShapedGlyph
    {
        public ushort Codepoint;
        public SKPoint Position;
        public float Width;
    }

    internal struct DrawTextCommand
    {
        public SKTextBlob SkTextBlob;
        public float TextOffsetX;
    }
    
    internal class TextShapingResult
    {
        public ShapedGlyph[] Glyphs { get; }

        public TextShapingResult(ShapedGlyph[] glyphs)
        {
            Glyphs = glyphs;
        }

        public int BreakText(int startIndex, float maxWidth)
        {
            var index = startIndex;
            maxWidth += Glyphs[startIndex].Position.X;

            while (index < Glyphs.Length)
            {
                var glyph = Glyphs[index];
                
                if (glyph.Position.X + glyph.Width > maxWidth + Size.Epsilon)
                    break;
                
                index++;
            }

            return index - 1;
        }
        
        public float MeasureWidth(int startIndex, int endIndex)
        {
            if (Glyphs.Length == 0)
                return 0;
            
            var start = Glyphs[startIndex];
            var end = Glyphs[endIndex];

            return end.Position.X - start.Position.X + end.Width;
        }
        
        public DrawTextCommand? PositionText(int startIndex, int endIndex, TextStyle textStyle)
        {
            if (Glyphs.Length == 0)
                return null;

            if (startIndex > endIndex)
                return null;
            
            using var skTextBlobBuilder = new SKTextBlobBuilder();
            
            var positionedRunBuffer = skTextBlobBuilder.AllocatePositionedRun(textStyle.ToFont(), endIndex - startIndex + 1);
            var glyphSpan = positionedRunBuffer.GetGlyphSpan();
            var positionSpan = positionedRunBuffer.GetPositionSpan();
                
            for (var sourceIndex = startIndex; sourceIndex <= endIndex; sourceIndex++)
            {
                var runIndex = sourceIndex - startIndex;
                
                glyphSpan[runIndex] = Glyphs[sourceIndex].Codepoint;
                positionSpan[runIndex] = Glyphs[sourceIndex].Position;
            }
            
            return new DrawTextCommand
            {
                SkTextBlob = skTextBlobBuilder.Build(),
                TextOffsetX = -Glyphs[startIndex].Position.X
            };
        }
    }
    
}