EMF+ pen strokes

TortoiseIDiff delegates metafile playback to Windows GDI+. TurtleGit renders captured WMF/EMF bytes through its private helper and displays the result in the same native image panes. This extension supplies the connected EMF+ pen object and stroke family; it does not change original repository bytes or conflict-side selection.

Source contracts

The binary layout follows Microsoft's EmfPlusPen object, PenData, compound line array and embedded brush. The brush contains its own GraphicsVersion before its brush type and payload, as shown in Microsoft's pen record example. The older synthetic alpha-pen fixture omitted this nested version; its framing is corrected while retaining its alpha/color expectations.

Pen::SetTransform transforms the pen nib independently of the centerline and ignores translation. SetCompoundArray requires an ordered positive even array of fractions between zero and one. SetAlignment disallows inset compound strokes and inset triangular dash caps. The LineJoin enumeration distinguishes Miter (limit clipping) from MiterClipped (bevel fallback); their names must not be mapped directly to CoreGraphics' single miter style.

The user-provided layout2vector writer provides an independent object writer reference. The BaseHmiTypes renderer remains the reference for the previously adapted classic clipping lifecycle, whose retained license and source pin accompany the helper. Neither package is installed as a runtime dependency. The pen geometry implementation uses system CoreGraphics and bounded local geometry construction.

Implementation and acceptance

src/turtleGitPens.js in the reconstruction patch parses the complete pen header and embedded brush, retaining linear nib transforms, independent standard start/end caps and anchors, four joins, miter limits, predefined/custom dashes, dash offsets and flat/round/triangular dash caps. Center/inset positioning and ordered compound bands feed the same native outline bridge. Custom dash patterns may have odd counts; their repeated pattern retains alternating on/off lengths. World-unit width stays in world coordinates; physical/pixel units are converted to the current page units before applying the outer page/world transform.

All nine stroke record families use this bridge: DrawLines, DrawRectangles, DrawEllipse, DrawPie, DrawArc, DrawPath, DrawClosedCurve, DrawCurve and DrawBeziers. Compressed coordinates are decoded where defined. DrawLines, DrawBeziers and DrawClosedCurve also accept relative integer coordinates; closed curves require at least three points. DrawCurve honors its starting offset and segment count while retaining neighboring points for cardinal-spline tangents. Arc/Pie sweep is bounded to a full turn while preserving the original start angle. Legal alignment padding is ignored.

Pen brush painting reuses the existing solid, gradient, hatch and texture pipeline, using actual outline bounds. The stroke receipt is cleared after each record, including exceptions, so a later classic GDI stroke cannot inherit an EMF+ pen. World/page transforms and captured clipping belong to the record playback lifecycle; a pen transform must not apply either a second time or move the centerline.

NativeStrokeGeometry receives only generated path commands and the captured pen options. Nonzero widths transform the centerline into nib space, construct stroke outlines and transform those outlines back; zero-width hairlines are constructed at one device pixel. Curves use bounded adaptive flattening, including collinear backtracking, before offset strips, joins, caps and compound bands are constructed. CoreGraphics normalizes the union of these primitives. Closed inset strokes intersect widened outlines with the original closed figure, while dash spacing continues to use the original width. Open inset paths remain centered. The target flattening error is 0.05 device pixel under the captured affine scale.

Native construction is limited across each conversion to 1,048,576 flattened points, 32,768 primitive polygons, 131,072 outline points before normalization and 32 MiB of outline markup. Each native input path is limited to 2 MiB and 262,144 generated commands; each normalized result to 131,072 serialized points. Arcs permit at most 65,536 subdivisions and cubic recursion stops at depth 24. The native 2 MiB path limit is stricter than the JavaScript bridge's 8 MiB guard. These limits bound construction before native Boolean normalization.

Binary construction limits include 64 object slots, 65,536 points per record, 4,096 rectangles per record, 1,048,576 aggregate stroke points, 1,024 custom dash entries and 1,024 compound fractions. Pen width and converted width cannot exceed 65,536; miter limits are between one and 65,536. The JavaScript bridge bounds individual native output paths to 32 MiB, with finite bounds no larger than 1,000,000,000 coordinate units. These limits reject oversized input explicitly; they do not silently simplify a drawing.

Verification

The batch checkpoint records 89 accepted and 55 refused fixtures, seven new Core methods, all executed attempts and their limits. The pixel oracles examine every pixel away from independently defined antialias boundaries, using signed-distance shapes and separate brush-fill controls. They include transformed and reversed bands, miter clipping, ordinary and dash caps, inset dash spacing, world/physical units, device hairlines, compressed/relative records, cardinal segment selection and backtracking cubics. A thin-band fixture was strengthened to keep real interior pixels after its antialias exclusion; assertions were retained.

The initial 50-method metafile group exposed compound-corner gap overpainting and a stationary-tangent curve subdivision failure. Offset-intersection trimming and analytic derivative-root splitting repair those cases. Only the two affected methods were repeated after the repair, and both passed; the other 48 initial passes are retained. The checkpoint separates this local arm64 corpus from the universal validator's generic WMF conversion/rejection checks on both slices.

The Debug app build and both system/bundled-Git native consumer runs passed. The consumer group uses 39 representative images, including six new pen samples, through actual image panes and retains original bytes, explicit Merge routing, preview/reload, conflict-stage selection and cancellation/late-result ownership checks. Both owned receiver processes were reaped and independently absent. These unbundled Debug receivers use the development helper; the prepared, packaged and current helper source identities were separately checked for equality. This is distinct from signed-parent execution or physical Finder acceptance.

Remaining compatibility

Custom line-cap objects have a connected custom-cap family with default fill/stroke paths, adjustable arrows and separate analytic/native evidence. The file-format-only Left, Outset and Right alignments are explicitly unsupported; the public GDI+ Pen API exposes Center and Inset. Unknown enums and malformed optional arrays are refused. Inset with compound bands or triangular dash caps is refused as an invalid API combination. This extension does not finish every classic EMF/WMF variant. The connected classic extended-pen family adds EMR_EXTCREATEPEN arrays, stroke brushes and bounded InsideFrame/state consumers; its checkpoint is recorded separately. Other painting records, alternate record formats and Windows font substitution remain separate compatibility work. The existing anti-alias, pixel-offset and compositing-quality records do not select GDI+ rasterization quality or its pixel grid. Standard anchor dimensions are compared with the Wine GDI+ implementation policy; a Windows capture oracle is still needed to certify their exact metrics. Windows pixel certification, every pathological self-intersection, platform edge antialiasing, minimum-OS execution, physical Finder acceptance and signed release acceptance require their own evidence. Successful source parsing or SVG emission alone does not establish correct native painting or complete TortoiseGit parity.