[Lakritzator]

Requested by Robin · project thread

Why

Greenshot needs to know which formats WIC can read and write. The registry key of the WIC decoder category (HKCR\CLSID\{7ED96837-...}\Instance) lists only 2 of 14 decoders on Windows 11 26300, because the built-in and the packaged (Store) codecs aren't in it. Going through WPF for loading and saving also can't reach every codec (JPEG XL "no imaging component", a NullReferenceException in the HEIF encoder). This adds a new package that uses WIC directly, with no WPF, no System.Drawing and no other pixel library.

What

New package Dapplo.Windows.Imaging (net480 and net10.0-windows, references Com and Common):

• Discovery: WicCodecs.GetDecoders(refresh) / GetEncoders(refresh) use IWICImagingFactory::CreateComponentEnumerator. WicCodecInfo reports kind, CLSID, container format, vendor, friendly name, author, version, extensions (lower case, with the dot), MIME types and signing status. A codec that can't be read is skipped and logged.
• Encode: WicImage.Encode takes either a pointer and stride (read through a Dapplo IWICBitmapSource, so the image isn't copied) or a WicRowProvider callback (the encoder pulls the rows it needs). Options are ImageQuality, Lossless and any encoder option by name; options an encoder doesn't have are skipped. GetEncoderOptions lists what an encoder supports. WIC converts the pixel format when needed, and indexed formats (GIF) get a palette.
• Decode: GetFrameInfo, and Decode into caller memory, into memory supplied once the size is known (one pass, e.g. a locked Bitmap), or to a WicRowConsumer. applyOrientation applies the EXIF orientation via IWICBitmapFlipRotator.
• No codec: WicCodecNotFoundException (a COMException) for WINCODEC_ERR_COMPONENTNOTFOUND and WINCODEC_ERR_COMPONENTINITIALIZEFAILURE. If a stream or callback throws, that exception reaches the caller unchanged.
• Metadata: this is a generic layer over the query language.
  • WicMetadata holds all items with friendly paths (/app1/ifd/exif/...; the tag paths work as aliases too), plus TryGet, TryGetRational, Orientation, the ICC ColorProfile, and EXIF/XMP/IPTC RawBlocks.
  • WicMetadataWriter has Set, Remove, SetColorProfile and AddRawBlock. When the encoder doesn't accept something, it is reported in WicEncodeResult.MetadataIssues and doesn't fail the encode.
  • PROPVARIANT mapping covers strings (LPSTR/LPWSTR), integers, floats, bool, rationals, FILETIME, GUID, blobs/vectors and nested blocks. WicMetadataPaths gives the paths for each container.
• Streams are .NET Streams through a small IStream adapter. It works on part of a larger stream, and non-seekable streams go through a MemoryStream. COM objects are created per call and released deterministically, and calls work from STA and MTA threads.

Interop: every vtable was checked against wincodec.idl / wincodec.h / wincodecsdk.h / ocidl.h from the Windows SDK. Docs: doc/articles/imaging.md with compiled samples (ImagingSamples), plus the codec/path matrix, README, CHANGELOG [3.18.0] and version.json 3.18.

Tests

On the CI runner (Windows Server 2025), 0 tests fail on net10 and net48.

• Discovery, including STA and MTA.
• PNG/TIFF round trips with both encode overloads and both decode overloads.
• 24bpp at width 63 with a padded stride.
• JPEG XR lossless.
• JPEG quality applied.
• Streams that can't seek, and offsets inside a larger stream.
• A row callback that throws.
• Unknown container or data gives WicCodecNotFoundException.
• Metadata paths, policies and ICC for JPEG/TIFF/PNG/JPEG XR.
• All 8 orientations.
• Unsupported queries are reported.
• Raw EXIF/XMP carry-over.
• GIF with transparency.

The runner has the HEIF and JPEG XL codecs registered, but their encoders fail with 0x88982F8B there. So JpegXl_LosslessRoundTrip and Heif_EncodeDecode are skipped on CI. Please run those two on a machine where the encoders work.

Follow-up (not in this PR)

Greenshot: reference the package, replace WpfFileFormatHandler.RetrieveDecoders() with WicCodecs.GetDecoders(), load and save through WicImage, and add the DLL to core-files.iss.

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Generated by Claude Code

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[coveralls]

Coverage Report for CI Build 41442041037

Coverage increased (+2.4%) to 54.23%

Details

• Coverage increased (+2.4%) from the base build.
• Patch coverage: 290 uncovered changes across 14 files (1011 of 1301 lines covered, 77.71%).
• No coverage regressions found.

Uncovered Changes

Top 10 Files by Coverage Impact	Changed	Covered	%
src/Dapplo.Windows.Imaging/Interop/PropVariant.cs	183	75	40.98%
src/Dapplo.Windows.Imaging/WicImage.cs	326	281	86.2%
src/Dapplo.Windows.Imaging/Internal/ManagedIStream.cs	102	66	64.71%
src/Dapplo.Windows.Imaging/Internal/WicMetadataReading.cs	174	148	85.06%
src/Dapplo.Windows.Imaging/WicMetadataWriter.cs	124	101	81.45%
src/Dapplo.Windows.Imaging/Internal/WicPixelSource.cs	65	51	78.46%
src/Dapplo.Windows.Imaging/WicCodecs.cs	70	58	82.86%
src/Dapplo.Windows.Imaging/WicMetadata.cs	51	43	84.31%
src/Dapplo.Windows.Imaging/WicRational.cs	24	18	75.0%
src/Dapplo.Windows.Imaging/WicFrameInfo.cs	20	16	80.0%
Total (22 files)	1301	1011	77.71%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	11410
Covered Lines:	6393
Line Coverage:	56.03%
Relevant Branches:	6272
Covered Branches:	3196
Branch Coverage:	50.96%
Branches in Coverage %:	Yes
Coverage Strength:	1038.49 hits per line

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💛 - Coveralls

[Lakritzator]

The build check on c02fdaf failed on net10 in two UiAutomationScrollerTests (ClosedWindow_EndsLoops, Wpf_HasNoWin32ScrollBar) with TimeoutException: The test window WpfScrollTestWindow didn't start. That isn't this PR's: the diff doesn't touch UI Automation or the WPF test window, net48 passed in the same job, and the other build run on the same commit passed. I re-ran the failed job once.

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Generated by Claude Code