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PngByteQRCode: use ArrayPool.Rent to prevent byte[] allocation #615

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Merged
Shane32 merged 3 commits into from
Oct 1, 2025
Merged

PngByteQRCode: use ArrayPool.Rent to prevent byte[] allocation #615

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ea16006
feat: use `ArrayPool.Rent` to prevent `byte[]` allocation
TimothyMakkison Oct 1, 2025
4af1e23
chore: fix whitespace
TimothyMakkison Oct 1, 2025
4b61cdc
Merge branch 'master' into arraypool_pngbyte
Shane32 Oct 1, 2025
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35 changes: 26 additions & 9 deletions QRCoder/PngByteQRCode.cs
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Original file line number Diff line number Diff line change
@@ -1,3 +1,6 @@
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1
using System.Buffers;
#endif
using System;
using System.IO;
using System.IO.Compression;
Expand Down Expand Up @@ -36,7 +39,11 @@ public byte[] GetGraphic(int pixelsPerModule, bool drawQuietZones = true)
using var png = new PngBuilder();
var size = (QrCodeData.ModuleMatrix.Count - (drawQuietZones ? 0 : 8)) * pixelsPerModule;
png.WriteHeader(size, size, 1, PngBuilder.ColorType.Greyscale);
png.WriteScanlines(DrawScanlines(pixelsPerModule, drawQuietZones));
var scanLines = DrawScanlines(pixelsPerModule, drawQuietZones);
png.WriteScanlines(scanLines);
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1
ArrayPool<byte>.Shared.Return(scanLines.Array!);
#endif
png.WriteEnd();
return png.GetBytes();
}
Expand Down Expand Up @@ -68,7 +75,11 @@ public byte[] GetGraphic(int pixelsPerModule, byte[] darkColorRgba, byte[] light
var size = (QrCodeData.ModuleMatrix.Count - (drawQuietZones ? 0 : 8)) * pixelsPerModule;
png.WriteHeader(size, size, 1, PngBuilder.ColorType.Indexed);
png.WritePalette(darkColorRgba, lightColorRgba);
png.WriteScanlines(DrawScanlines(pixelsPerModule, drawQuietZones));
var scanLines = DrawScanlines(pixelsPerModule, drawQuietZones);
png.WriteScanlines(scanLines);
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1
ArrayPool<byte>.Shared.Return(scanLines.Array!);
#endif
png.WriteEnd();
return png.GetBytes();
}
Expand All @@ -79,13 +90,19 @@ public byte[] GetGraphic(int pixelsPerModule, byte[] darkColorRgba, byte[] light
/// <param name="pixelsPerModule">The number of pixels each dark/light module of the QR code will occupy in the final QR code image.</param>
/// <param name="drawQuietZones">Indicates if quiet zones around the QR code should be drawn.</param>
/// <returns>Returns the bitmap as a byte array.</returns>
private byte[] DrawScanlines(int pixelsPerModule, bool drawQuietZones)
private ArraySegment<byte> DrawScanlines(int pixelsPerModule, bool drawQuietZones)
{
var moduleMatrix = QrCodeData.ModuleMatrix;
var matrixSize = moduleMatrix.Count - (drawQuietZones ? 0 : 8);
var quietZoneOffset = (drawQuietZones ? 0 : 4);
var bytesPerScanline = (matrixSize * pixelsPerModule + 7) / 8 + 1; // A monochrome scanline is one byte for filter type then one bit per pixel.
var scanlines = new byte[bytesPerScanline * matrixSize * pixelsPerModule];
var scanLinesLength = bytesPerScanline * matrixSize * pixelsPerModule;
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1
var scanlines = ArrayPool<byte>.Shared.Rent(scanLinesLength);
Array.Clear(scanlines, 0, scanLinesLength);
#else
var scanlines = new byte[scanLinesLength];
#endif

for (var y = 0; y < matrixSize; y++)
{
Expand Down Expand Up @@ -115,7 +132,7 @@ private byte[] DrawScanlines(int pixelsPerModule, bool drawQuietZones)
}
}

return scanlines;
return new ArraySegment<byte>(scanlines, 0, scanLinesLength);
}

/// <summary>
Expand Down Expand Up @@ -249,7 +266,7 @@ public void WritePalette(params byte[][] rgbaColors)
/// <summary>
/// Writes the IDAT chunk with the actual picture.
/// </summary>
public void WriteScanlines(byte[] scanlines)
public void WriteScanlines(ArraySegment<byte> scanlines)
{
using var idatStream = new MemoryStream();
Deflate(idatStream, scanlines);
Expand All @@ -268,7 +285,7 @@ public void WriteScanlines(byte[] scanlines)
idatStream.CopyTo(_stream);
#endif
// Deflate checksum.
var adler = Adler32(scanlines, 0, scanlines.Length);
var adler = Adler32(scanlines.Array!, 0, scanlines.Count);
WriteIntBigEndian(adler);

WriteChunkEnd();
Expand Down Expand Up @@ -304,10 +321,10 @@ private void WriteIntBigEndian(uint value)
_stream.WriteByte((byte)value);
}

private static void Deflate(Stream output, byte[] bytes)
private static void Deflate(Stream output, ArraySegment<byte> bytes)
{
using var deflateStream = new DeflateStream(output, CompressionMode.Compress, leaveOpen: true);
deflateStream.Write(bytes, 0, bytes.Length);
deflateStream.Write(bytes.Array!, 0, bytes.Count);
}

// Reference implementation from RFC 1950. Not optimized.
Expand Down