Positioned metafile text in image comparison

Pinned TortoiseGit: 7338078f8ddd924b8cddee35f512f2286072136d. Its image viewer accepts Windows metafiles through GDI+. This connected family adds positioned text to the existing macOS decoder used by comparison panes, dropped previews and image conflicts. It complements formatted DrawString layout, whose shaping and wrapping contract is separate from caller-positioned glyphs.

Record and font contract

Microsoft's DrawDriverString record distinguishes character-map values from font-specific glyph indices. The decoder must preserve that distinction: a glyph index cannot become a Unicode character. The wire array contains a position slot for each input value. RealizedAdvance uses the initial position and native advances; it does not shorten the serialized array. An optional six-component matrix follows the complete arrays.

The driver options also distinguish vertical output and a raster-cache quality hint. CoreText supplies native font outlines and advances. Caller-positioned text must not receive the paragraph shaping, wrapping or implicit reordering of DrawString. Raw glyphs require the requested installed font; substituting an unrelated font would change what the indices mean. Font availability and exact Windows glyph metrics remain independent compatibility limits.

The driver matrix acts on font geometry and advance vectors about each supplied origin. Graphics-world mapping acts on positions separately. Ignoring the driver matrix's translation follows the inspected Wine GDI+ implementation, which builds font vectors from that matrix. For vertical output, its Prepend composition applies the driver linear transform before the clockwise quarter turn. A noncommuting transform must distinguish that order from turning first. These interpretations have no independent Windows capture yet and must not be described as pixel-certified Windows playback.

Classic EMR_EXTTEXTOUTW uses the selected LOGFONT and EmrText offsets. Its optional spacing array affects actual character origins. ETO_PDY provides paired horizontal and vertical advances. The complete buffer extents, alignment and record-relative offsets must be checked before font work. Source alignment, background and clipping belong to the same text operation, with current-position state preserved through graphics Save/Restore.

SetTextAlign makes the saved current position the reference when TA_UPDATECP is set. The inspected Wine font implementation advances it to the right edge for left alignment, moves it to the left edge for right alignment, and retains it for centered alignment. Vertical baseline adjustment does not change this continuation point. Fixtures must distinguish these cases rather than testing only a single left-aligned string.

The selected LOGFONT distinguishes cell height from em height, and escapement from glyph orientation in advanced graphics mode. An explicit average width scales font vectors using the selected font's OS/2 average-width metric. Actual glyph advances still come from CoreText; the average metric does not replace each glyph's width. Missing or invalid required font metrics must cause an explicit refusal. Native scalable-font metrics do not certify Windows font mapper selection, raster-font sizing or device-specific rounding.

Shared native ownership

The existing helper remains the only conversion process. Positioned glyphs share the formatted-text conversion's aggregate input, glyph, outline and serialized path budgets. Repeated records cannot acquire fresh per-record work allowances. Native outlines return through the same JavaScriptCore boundary without exposing font-file paths, filesystem, network or executable access to the document.

The existing image operation owns cancellation and process drain. Original repository, preview and conflict bytes remain unchanged; outlines are private display data. Text decorations, brushes, clipping, transforms and bounds must be reviewed together rather than accepting a valid-looking but incomplete string.

Accepted scope and explicit limits

Driver output supports supplied positions, RealizedAdvance, Unicode character-map lookup or raw glyph indices, vertical rotation, linear matrices, existing brushes and captured graphics clips. LimitSubpixel is retained as a quality hint; vector outlines have no GDI glyph bitmap cache to reduce. Valid surrogate pairs map to one glyph cluster at the first UTF-16 position, while malformed pairs fail. Raw glyph output requires an installed matching face and style. Unicode lookup can use native font substitution but receives no paragraph shaping.

Classic W output supports ETO_OPAQUE, ETO_CLIPPED, ETO_GLYPH_INDEX, ETO_PDY and the ETO_IGNORELANGUAGE metadata flag. Each supplied displacement contributes, including the final advance used for alignment and continuation. Positive PDY moves upwards in source font coordinates. Advanced graphics mode retains affine geometry and independent escapement/orientation; compatible mode compensates reflected device axes. Compatible font ink and native advances use the font's vertical device scale, independently of the full mapping of supplied spacing. The glyph and layout compensation matrices preserve those separate rules. Record exScale/eyScale remain finite conversion metadata; ExtTextOutW playback does not apply them again over the captured device context. Explicit rectangle backgrounds and clipping use ordered device corners. An opaque background without an explicit rectangle uses the native cell metrics. Transparent BeginPath text accumulates glyph outlines.

Opaque BeginPath text, empty driver records, locale/numeric/RTL text options and other classic record variants remain outside this implementation. The retained ANSI path refuses glyph-index input explicitly. Native font metrics, vertical-specific CJK forms, Windows-only font families, bitmap/color-only glyphs and exact GDI rasterization remain compatibility limits. A refusal returns no successful partial image.

Each positioned call is limited to 32,768 UTF-16 values or glyph indices. The shared conversion allows 262,144 text units and glyph work items, two million outline elements and 32 MiB of serialized text paths. Input coordinates, affine matrices, selected-font glyph counts, generated bounds and font metrics are checked. These work limits can refuse otherwise valid large Windows inputs.

Implementation checkpoint

The implementation contains 52 original accepted pictures and 22 refusal fixtures. All 616 earlier WMF/EMF fixture hashes remain unchanged. Private raw glyph records derive their indices from the installed Helvetica cmap at runtime, so the corpus does not assume fixed glyph numbers across macOS font versions. Independent positions, font metrics and noncommuting matrices distinguish spacing and orientation errors. The eight new Core methods and native image consumer group cover these connected behaviors.

The dated record records the passing universal runtime, both architecture conversions, Debug app build, 21 distinct relevant Core methods and the grouped native consumers with system and bundled Git. The initial Core group passed 20 of 21 methods. Its failed cell-height assertion assumed Helvetica's cell height differed from its em height, while the actual native metrics were equal. New Arial cell/em controls preserve the strict geometry assertion; only that affected method was repeated, and passed.

The native group uses 11 representative pictures and two private cmap-derived raw-glyph records. Actual comparison panes, dropped previews, three-stage image conflicts, malformed refusal and chooser/cancellation/late-result/grant/Quit ownership passed with original bytes and repository state preserved. Test windows were invisible and both receivers were reaped. These linked Debug consumers use the development helper; separate embedded renderer/source identity checks do not prove physical UI or distribution-signed execution.

The packaged Debug renderer matches the reconstructed runtime. Its manifest retains the matching unsigned helper hash beneath ad-hoc signing. No complete hosted CI, Windows font/raster identity, physical image-window or App Store acceptance is established by this focused checkpoint.