Simple PDF Example

pdf.dart

// dart run bin/make_pdf.dart
import 'dart:io';
import 'dart:typed_data';

void main() async {
  final pdf = _PdfBuilder();

  // Register built-in Type1 fonts (Base-14): Helvetica & Helvetica-Bold
  final fontRegular = pdf.addRawObject(
    '<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >>',
  );
  final fontBold = pdf.addRawObject(
    '<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica-Bold /Encoding /WinAnsiEncoding >>',
  );

  // Page size: A4 (points)
  const mediaBox = '[0 0 595 842]';

  // Build content stream: simple formatted text
  final content =
      StringBuffer()
        // Begin text object
        ..writeln('BT')
        // Set text leading (line spacing)
        ..writeln('14 TL')
        // Move to start position (x=72pt, y=770pt)
        ..writeln('72 770 Td')
        // Regular text, 12pt
        ..writeln('/F1 12 Tf')
        ..writeln('(Hello, PDF from pure Dart) Tj')
        // New line: move down by 24pt
        ..writeln('0 -24 Td')
        // Bold text, larger size
        ..writeln('/F2 18 Tf')
        ..writeln('(Bold headline) Tj')
        // New line
        ..writeln('0 -28 Td')
        // Back to regular 12pt
        ..writeln('/F1 12 Tf')
        ..writeln('(Left-aligned line) Tj')
        // New line + little indent to the right
        ..writeln('0 -18 Td 24 0 Td')
        ..writeln('(Indented line) Tj')
        // Another paragraph: reset X to 72pt, move further down
        ..writeln('T* T*') // two line feeds using TL
        ..writeln('ET'); // End text object

  final contentStreamObj = pdf.addStreamObject(
    content.toString(),
    // Resources: reference fonts
    // We'll attach resources on the Page object; stream only needs /Length
  );

  // Page object with resources (font dictionary)
  final pageObj = pdf.addRawObject('''
<< /Type /Page
   /Parent 2 0 R
   /MediaBox $mediaBox
   /Resources << /Font << /F1 ${fontRegular.id} 0 R /F2 ${fontBold.id} 0 R >> >>
   /Contents ${contentStreamObj.id} 0 R
>>
''');

  // Pages tree
  final pagesObj = pdf.addRawObject('''
<< /Type /Pages
   /Kids [ ${pageObj.id} 0 R ]
   /Count 1
>>
''');

  // Catalog
  final catalogObj = pdf.addRawObject('''
<< /Type /Catalog
   /Pages ${pagesObj.id} 0 R
>>
''');

  // Finalize and write to file
  final bytes = pdf.build(catalogObjId: catalogObj.id);
  final file = File('sample.pdf');
  await file.writeAsBytes(bytes, flush: true);
  stdout.writeln('Written: ${file.absolute.path}');
}

/// Very small PDF builder that can emit:
/// - Header, numbered indirect objects
/// - Stream objects with correct /Length
/// - xref table, trailer, startxref
class _PdfBuilder {
  // 1-based IDs in output order

  _PdfBuilder() {
    // PDF header; the binary comment line helps some readers detect binary data
    _write('%PDF-1.4\n');
    _write('%\xFF\xFF\xFF\xFF\n');
  }
  final BytesBuilder _buf = BytesBuilder();
  final List<_Obj> _objects = [];

  _Obj addRawObject(String body) {
    final id = _objects.length + 1;
    final obj = _Obj(id: id, isStream: false, body: body);
    _objects.add(obj);
    return obj;
  }

  _Obj addStreamObject(String streamData) {
    final id = _objects.length + 1;
    final obj = _Obj(id: id, isStream: true, body: streamData);
    _objects.add(obj);
    return obj;
  }

  Uint8List build({required int catalogObjId}) {
    // Write all objects, recording their byte offsets
    final offsets = <int>[0]; // dummy at index 0 to keep 1-based indexing
    for (final obj in _objects) {
      offsets.add(_offset);
      _write('${obj.id} 0 obj\n');
      if (obj.isStream) {
        final data = obj.body;
        final length = data.codeUnits.length;
        _write('<< /Length $length >>\n');
        _write('stream\n');
        _write(data);
        if (!data.endsWith('\n'))
          _write('\n'); // ensure newline before endstream
        _write('endstream\n');
        _write('endobj\n');
      } else {
        _write('${obj.body.trimRight()}\n');
        _write('endobj\n');
      }
    }

    // xref
    final xrefStart = _offset;
    _write('xref\n');
    _write('0 ${_objects.length + 1}\n');
    // Object 0 entry (free)
    _write('0000000000 65535 f \n');
    // Object entries
    for (final off in offsets.skip(1)) {
      _write(_fmt10(off));
      _write(' 00000 n \n');
    }

    // trailer
    _write('trailer\n');
    _write('<< /Size ${_objects.length + 1} /Root $catalogObjId 0 R >>\n');
    _write('startxref\n');
    _write('$xrefStart\n');
    _write('%%EOF\n');

    return _buf.toBytes();
  }

  // Helpers
  void _write(String s) => _buf.add(s.codeUnits);
  int get _offset => _buf.length;

  String _fmt10(int v) {
    // 10-digit, zero-padded
    final s = v.toString();
    if (s.length >= 10) return s.substring(s.length - 10);
    return '0' * (10 - s.length) + s;
  }
}

class _Obj {
  _Obj({required this.id, required this.isStream, required this.body});
  final int id;
  final bool isStream;
  final String body;
}