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Enhanced ZLib Compression Support
Overview
HotPDF now includes comprehensive ZLib-compatible compression support backed by bundled zlib-ng for PDF streams and content.
The zlib-compatible API provides efficient deflate/inflate compression that is widely used in PDF documents for
FlateDecode filter operations and general data compression.
Key Features
- ZLib-compatible API backed by bundled zlib-ng
- PDF FlateDecode parameters support
- Stream-based compression and decompression
- Enhanced error handling and debugging capabilities
- Memory-efficient processing for large data streams
- Win64 one-shot image compression bridge for zlib-ng length ABI safety
- Win64x and diagnostic MSVC Win64 zlib-ng runtime SIMD dispatch with generic fallbacks
- 32-byte aligned C allocation bridge for SIMD-friendly native buffers
- Cross-platform C library integration
- Multiple compression levels (none, fastest, default, maximum)
Technical Implementation
The enhanced ZLib support is implemented through the HPDFZLib.pas unit, which provides:
- Complete ZLib API: Full implementation of ZLib functions
- Stream Classes: TCustomZStream and derived classes for stream processing
- PDF Integration: TPDFFlateParms for PDF-specific parameters
- Enhanced Functions: InflateStr, InflateStrParms for simplified usage
The 64-bit zlib-ng object sets include runtime-selected SSE2, SSSE3, SSE4.1, SSE4.2, PCLMULQDQ, and AVX2 paths. Win32 uses the generic zlib-ng object set to stay compatible with the bcc32c OMF toolchain, while Win32 JPEG/TIFF objects remain on classic bcc32.
Regression Coverage
The zlib-ng Flate backend is covered by the automated Delphi and C++Builder regression suites. The current validation set passes 20 Delphi DUnitX tests on Win32 and 20 on Win64, plus 17 C++Builder GoogleTest tests on Win32 and 17 on Win64x. The native object rebuilds also pass from clean outputs: 206 Win32 objects, 205 Win64x objects, and 206 MSVC Win64 objects. The covered workflows include page-stream compression, embedded font and ToUnicode CMap compression, Flate image streams, standard JPEG image placement, TIFF import, barcode-heavy output, copy/merge/edit scenarios, and demo-generated PDFs.
Compression Levels
- Z_NO_COMPRESSION (0): No compression
- Z_BEST_SPEED (1): Fastest compression
- Z_BEST_COMPRESSION (9): Maximum compression
- Z_DEFAULT_COMPRESSION (-1): Default balance of speed and compression
Usage Examples
Basic String Compression/Decompression
// Delphi example - Basic string inflation
function DecompressString(const CompressedData: AnsiString): AnsiString;
begin
// Simple decompression
Result := InflateStr(CompressedData);
// With debug output enabled
Result := InflateStr(CompressedData, True);
end;
Stream-based Compression
// Delphi example - Stream-based decompression
procedure DecompressStream(InStream, OutStream: TStream);
begin
// Decompress from input stream to output stream
PLZDecompressStream(InStream, OutStream);
// For raw deflate data (without ZLib headers)
PLZDecompressStreamRaw(InStream, OutStream);
end;
PDF FlateDecode with Parameters
// Delphi example - PDF FlateDecode with parameters
function DecompressPDFStream(const CompressedData: AnsiString;
Predictor, Colors, BitsPerComponent, Columns: Integer): AnsiString;
var
Parms: TPDFFlateParms;
begin
// Configure PDF parameters
Parms.Predictor := Predictor;
Parms.Colors := Colors;
Parms.BitsPerComponent := BitsPerComponent;
Parms.Columns := Columns;
Parms.ExpandedTo8Bit := True;
Parms.ColorSpace := 'DeviceRGB';
// Decompress with PDF parameters
Result := InflateStrParms(CompressedData, Parms);
end;
Low-level ZLib Operations
// Delphi example - Low-level ZLib operations
procedure CompressData;
var
strm: z_stream;
ret: Integer;
input: AnsiString;
output: AnsiString;
begin
input := 'Data to compress';
SetLength(output, Length(input) * 2);
// Initialize stream
FillChar(strm, SizeOf(strm), 0);
ret := deflateInit(strm, Z_DEFAULT_COMPRESSION);
if ret = Z_OK then
try
// Set input
strm.next_in := PByte(PAnsiChar(input));
strm.avail_in := Length(input);
// Set output
strm.next_out := PByte(PAnsiChar(output));
strm.avail_out := Length(output);
// Compress
ret := deflate(strm, Z_FINISH);
if ret = Z_STREAM_END then
begin
// Compression successful
SetLength(output, Length(output) - strm.avail_out);
end;
finally
deflateEnd(strm);
end;
end;
PDF FlateDecode Parameters
TPDFFlateParms Structure
- Predictor: Predictor function (1=no prediction, 2=TIFF, 10-15=PNG)
- Colors: Number of color components
- BitsPerComponent: Bits per color component
- Columns: Number of samples per row
- ExpandedTo8Bit: Whether to expand to 8-bit components
- ColorSpace: Color space identifier
Enhanced Features
- Memory Management: Optimized memory allocation and deallocation
- Error Handling: Comprehensive error checking and reporting
- Debug Support: Optional debug output for troubleshooting
- Performance Optimization: Highly optimized compression algorithms
- Stream Integration: Seamless integration with Delphi stream classes
Performance Benefits
- Fast compression and decompression speeds
- Excellent compression ratios for text and simple graphics
- Low memory footprint during processing
- Optimized for PDF content streams
- Minimal CPU overhead
Standards Compliance
- RFC 1950 (ZLib format specification)
- RFC 1951 (Deflate compression algorithm)
- PDF FlateDecode filter specification
- PNG predictor algorithm support
- TIFF predictor algorithm support
Error Codes and Handling
- Z_OK (0): Success
- Z_STREAM_END (1): End of stream reached
- Z_NEED_DICT (2): Dictionary required
- Z_ERRNO (-1): File error
- Z_STREAM_ERROR (-2): Stream state error
- Z_DATA_ERROR (-3): Data integrity error
- Z_MEM_ERROR (-4): Memory allocation error
- Z_BUF_ERROR (-5): Buffer size error
See Also
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