Base64Codec

ImageGlass Base64 Sample Codec Plugin

A minimal, cross-platform native codec plugin for ImageGlass v10 that teaches the in-process native plugin ABI (ImageGlass.SDK.Plugins / IGNativeAbi) with the smallest interesting codec: it adds support for .b64 files.

Extension	What it does
.b64 (read)	Reads a base64-encoded image from a text file and decodes it to a raster image
.b64 (write)	PNG-encodes the pixels the host hands over and writes the base64 of that PNG

A .b64 file is just a text file holding a base64 string. Two shapes are accepted on read; writing always emits shape 1:

1. A raw base64 payload – iVBORw0KGgoAAAANSUhEUgAA...
2. A data URI – data:image/png;base64,iVBORw0KGgo...

Whitespace and newlines anywhere in the payload are ignored. Because the write path uses PNG, a decode/encode round trip through ImageGlass is lossless.

What it demonstrates

• Exports the well-known C entry point ig_plugin_get_api
• Advertises one static-image codec (plugin.base64.codec) that both reads and writes .b64, via separate DecodeExtensions / EncodeExtensions lists
• Allocates the IGCodecCapability itself and returns it by pointer, and sets every StructSize it owns (IGPluginApi, IGCodecApi, IGCodecCapability)
• Implements LoadMetadata and DecodeStaticRaster:
  1. File.ReadAllText → strip an optional data:…;base64, prefix
  2. Convert.FromBase64String → original image bytes (PNG/JPEG/WebP/…)
  3. SKCodec decodes those bytes straight into a native 32bpp unpremultiplied BGRA buffer (IGPixelFormat.Bgra8Unorm)
• Implements EncodeStaticRaster: wraps the host's pixels with SKImage.FromPixelCopy, PNG-encodes, base64s, and writes the text file
• Reads IGEncodeOptions.Quality through a StructSize bounds check instead of assuming the field is present
• Allocates decode pixel buffers with NativeMemory.Alloc and releases them in a thread-safe FreePixelBuffer that only frees pointers it recorded itself, so a host-owned encode buffer can never be freed by mistake
• Honors the host-supplied opaque cancellation token at coarse boundaries
• Leaves the animation-decode and multi-frame-encode entry points null, showing that each capability quadrant is independently optional

Unlike a format-specific codec, the heavy lifting is delegated to SkiaSharp (the SDK's only dependency), so the plugin stays tiny and works on any platform SkiaSharp supports.

Build (Native AOT shared library)

dotnet publish samples/Base64Codec/Base64Codec.csproj `
    -c Release -r win-x64 -p:Platform=x64 `
    -o samples/Base64Codec/bin/publish/win-x64

This produces Base64Codec.dll next to igplugin.json. (Use -r linux-x64 / -r osx-arm64 and the matching -p:Platform for other targets.)

Publish, never dotnet build. A plain build emits the managed assembly, which exports no ig_plugin_get_api; the host loads the file and then skips the plugin. If a published Base64Codec.dll is only a few KB, it is the managed one, not the AOT library.

Package

Zip the published files for the host's Settings > Plugins > Add button. igplugin.json must sit at the archive root or one folder below it; skip the .pdbs.

Plugin_SampleBase64Codec.igplugin.zip
    Base64Codec.dll
    igplugin.json
    libSkiaSharp.dll

$src = "samples/Base64Codec/bin/publish/win-x64"
Compress-Archive -Path "$src/*.dll", "$src/igplugin.json" `
    -DestinationPath Plugin_SampleBase64Codec.igplugin.zip

Install

Copy the published folder (containing the DLL, igplugin.json, and the native libSkiaSharp asset emitted by the AOT publish) into the host's plugins dir:

%LOCALAPPDATA%\ImageGlass\_plugins\Base64Codec\
    Base64Codec.dll
    igplugin.json
    libSkiaSharp.dll

On next launch the host discovers the manifest, loads the DLL, calls ig_plugin_get_api, and registers plugin.base64.codec for .b64.

Try it

Create a test file from any image:

[Convert]::ToBase64String([IO.File]::ReadAllBytes("photo.png")) `
    | Set-Content -NoNewline test.b64

Open test.b64 in ImageGlass – it renders as the original image.

Then go the other way: open any JPG or PNG and use Save as with the .b64 type. Reopening the result renders the same image, proving the round trip.

Manifest schema

igplugin.json is deserialized into ImageGlass.SDK.Plugins.PluginManifest. Required fields: id, name, executable. The kind field defaults to "Codec" if omitted. There is no extension list in the manifest: the formats this codec reads and writes are declared in IGCodecCapability, and users narrow those sets in ImageGlass's plugin settings.

Notes

• Codec selection is priority-based. No built-in codec claims .b64, but the plugin still advertises metadataPriority/decodePriority/encodePriority of 200 so it reliably wins selection for that extension.
• Without this plugin, saving as .b64 fails: the entry exists in ImageGlass's Save As list but Magick.NET has no base64 coder. The plugin is what makes it work.
• Convert.FromBase64String ignores embedded whitespace, so wrapped/multi-line base64 files work without pre-processing.
• The codec reports IGColorSpace.Srgb; it does not extract embedded ICC profiles (SupportsColorProfiles = 0).