AstcSharp 3.0.0

AstcSharp

A pure C# library for decoding and encoding ASTC (Adaptive Scalable Texture Compression) textures, supporting both LDR and HDR content.

Features

• Managed C#, no native dependencies
• Stream-to-stream API (sync + async) that processes one block-row band at a time, bounding memory independently of image size
• Decode ASTC textures to RGBA32 (LDR) or RGBA float / FP16 (HDR)
• Encode RGBA32 LDR images to ASTC blocks
• Linear and sRGB LDR decode modes
• All standard block footprints (4x4 to 12x12)
• UASTC LDR decode (Basis Universal), via UastcDecoder — all 19 LDR modes (single/multi-subset, dual-plane, RGB/RGBA/LA, solid)

Installation

dotnet add package AstcSharp

Usage

The API is stream-to-stream: decode and encode read ASTC blocks / pixels from a source Stream and write the result to a destination Stream, processing one block-row band at a time so peak memory is bounded to a single band rather than the whole image. You pass the image dimensions and footprint explicitly — the source holds raw block/pixel data, not an .astc file header. Each method has a synchronous form and an Async form taking a CancellationToken.

Decoding

using AstcSharp;
using AstcSharp.Core;

var footprint = Footprint.FromFootprintType(FootprintType.Footprint4x4);
using var source = File.OpenRead("texture-blocks.bin"); // raw ASTC blocks
using var destination = new MemoryStream();

// LDR: decode to RGBA32
AstcDecoder.DecompressImage(source, destination, width, height, footprint);

// LDR sRGB: apply the spec's sRGB endpoint expansion (output stays sRGB-encoded)
AstcDecoder.DecompressImage(source, destination, width, height, footprint, LdrDecodeMode.Srgb);

// HDR: decode to RGBA float / FP16 Half, written as little-endian channels (RGBA, row-major)
AstcDecoder.DecompressHdrImage(source, destination, width, height, footprint);
AstcDecoder.DecompressHdrImageHalf(source, destination, width, height, footprint);

// Async (e.g. file/network streams)
await AstcDecoder.DecompressImageAsync(source, destination, width, height, footprint, cancellationToken: token);

// UASTC (Basis Universal, always 4x4): decode raw UASTC block data to RGBA8888
UastcDecoder.DecompressImage(uastcSource, destination, width, height);

Encoding

using var pixelSource = new MemoryStream(rgbaPixels); // RGBA32, row-major
using var blockDestination = new MemoryStream();

// Encode an RGBA32 LDR image to ASTC blocks
AstcEncoder.CompressImage(pixelSource, blockDestination, width, height, footprint);
await AstcEncoder.CompressImageAsync(pixelSource, blockDestination, width, height, footprint, token);

Performance

AstcSharp's decoding performance is competitive with ARM's C++ implementation, with some overhead due to being a pure C# implementation.

| Method           | Categories | Mean          | Error        | StdDev       | Ratio  | RatioSD | Allocated | Alloc Ratio |
|----------------- |----------- |--------------:|-------------:|-------------:|-------:|--------:|----------:|------------:|
| Arm_Decode       | Decode     |      37.62 us |     0.582 us |     0.486 us |   1.00 |    0.00 |         - |          NA |
| AstcSharp_Decode | Decode     |      26.53 us |     0.357 us |     0.316 us |   0.71 |    0.01 |         - |          NA |
|                  |            |               |              |              |        |         |           |             |
| Arm_Encode       | Encode     |     828.34 us |     8.152 us |     7.625 us |   1.00 |    0.00 |         - |          NA |
| AstcSharp_Encode | Encode     | 164,935.80 us | 2,025.726 us | 1,894.865 us | 199.13 |    2.42 |   16764 B |          NA |

Future improvements

• 3D block types
• HDR encoding (encoding currently supports LDR only)

References

This implementation is based on:

• ASTC Specification: Khronos Data Format Specification - The official ASTC texture compression format specification
• ARM ASTC Codec: github.com/ARM-software/astc-encoder
• Google astc-codec: github.com/google/astc-codec

License

See LICENSE for details.