Classic metafile direct scanlines and gradient meshes

Pinned TortoiseGit 7338078f8ddd924b8cddee35f512f2286072136d accepts WMF/EMF images through src/Utils/MiscUI/Picture.cpp and displays them in TortoiseIDiff. Windows GDI+ supplies the record playback. The native port must interpret those records before its existing Image Compare and image-conflict panes can display them. A previously rejected or ignored paint record is a missing image capability, not a missing file association.

Direct bitmap scanlines

EMR_SETDIBITSTODEVICE and META_SETDIBTODEV transfer specified source scanlines to the playback destination. Their framing is different: EMF declares record-relative bitmap information/pixel ranges, whereas WMF packs a DIB after its WORD parameters. The Win32 banding contract allows the pixel payload to contain only the selected scanline band. Requiring all declared bitmap rows would incorrectly reject those images.

The native reader keeps header dimensions, source coordinates, scanline start/count and supplied pixel storage separate. It validates offsets, row alignment, palette and channel formats, and complete required payloads before painting. Unprovided rows cannot become invented black image content. The operation copies source colors and does not inherit the selected pen's Boolean ROP2. Clipping, mapping and earlier destination drawing remain part of the shared playback pipeline.

Source-copy placement follows the Windows-compatible device behavior: the logical destination origin is mapped, while bitmap pixels keep device extents rather than being stretched or rotated as a complete rectangle. Source coordinates retain the lower-left convention independently of physical top-down/bottom-up row storage. WMF source/destination WORD coordinates are sign-extended for playback, while scan counts and extents retain unsigned fields. These compatibility details are checked against Wine 840a939ee526137639665ff5f587224d6a36403f: direct playback, independent API tests and WMF coordinate playback. No Wine implementation code is copied.

Full RLE, JPEG and PNG inputs use the applicable existing decoder. Partial compressed bands remain explicit refusals. Classic compressed input has its own opaque-color bridge: straight 8/16-bit RGB/grayscale channel storage retains its RGB samples while alpha becomes opaque. It does not blend a PNG over white and does not change the alpha-aware EMF+ image/texture bridge. Transparent premultiplied or unsupported channel packing is refused when original RGB cannot be proved from the supplied decoder representation.

Gradient meshes

EMR_GRADIENTFILL contains vertices followed by rectangle or triangle index meshes. Rectangle modes interpolate along their horizontal or vertical axis; triangle mode interpolates among three vertex colors. The Win32 record contract and TRIVERTEX color contract are separate from EMF+ gradient brush objects. The Alpha field is ignored for this classic record; it is not an alpha-gradient blend.

The native implementation evaluates the actual mesh instead of replacing each triangle with an average or two-color gradient. Device mapping and existing clips constrain the painted region. Mesh order, vertex indices, record extent and work budgets are validated. Rectangle and triangle records share bounded color interpolation, while retaining their distinct serialized framing. The normative rectangle record includes ignored padding after the index array. The exact compact Win32 structure representation is also accepted; partial padding or unrelated trailing bytes are refused. Triangle records have no such padding.

Rasterization uses intrinsic device-pixel centers and a single-coverage edge convention. It preserves mesh order, including overlaps, and affine reflection, rotation and shear. Bounded raster output does not promise vector-resolution zoom or the same antialiased edge pixels as every Windows driver.

Consumers and verification boundary

The bundled interpreter serves existing default comparisons, explicit IDiff and three-stage image conflicts. Decoded display pixels do not replace repository bytes. Selecting a conflict side copies that side's original metafile bytes, including records that are unrelated to the selected display operation.

The dated checkpoint records 16 focused Core methods passing: seven new scanline/gradient methods and nine related existing rendering methods. The rebuilt universal macOS13 helper passes source reconstruction and actual conversion/refusal checks on both architectures. The Debug app embeds matching renderer and source receipts. Four native case/engine pairs pass on the first run across system and bundled Git, including default/explicit comparison, malformed whole-image refusal, actual three-stage conflict resolution and held decoded-result retirement/Quit accounting.

The runtime's first compile required the missing Data(bytes:) constructor label; the successful rebuild includes a static WMF compressed-payload/padding repair. Core and native groups needed no repairs or repeats. All four owned receivers were reaped and independently absent, and completed requests fail validation if an approved helper outlives their private request. No new screenshots or literal native labels were needed. Help was regenerated before the app build; the source coverage ledger retains partial review status.

This family does not implement graph export to WMF/EMF, every Windows metafile record, Windows pixel/font identity, physical Intel/minimum-OS acceptance, or current signed/App Store distribution acceptance. Those remain separate from successful decoding of this record family.