General EMF+ path-gradient boundaries

The general boundary continuation adds cubic paths, multiple figures and self-intersections to the existing path-gradient renderer. It retains uniform and separate surrounding colors, the existing focus/preset/gamma rules, brush/world transforms, and the common fill, pen, glyph, clip and SourceCopy consumers. The canonical single-color ellipse keeps its existing analytic path. The rebuilt decoder passes 12 focused Core methods (six retained and six new) and the actual native Compare/Conflict workload with both system and bundled Git. The dated checkpoint records the reconstruction, passes, repairs and execution scope. This is acceptance of the bounded profile below, not complete metafile or application parity.

Microsoft's BoundaryPathData specification embeds an EmfPlusPath, while its GDI+ path-gradient examples describe paths containing lines and curves. Neither specifies enough raster behavior to infer contour order or cubic surrounding-color assignment. Two isolated Windows assays provide the independent reference:

Twelve native controls, revision dc16d3c42e5a246237d530e3dd53bd3c57db38b2: asymmetric cubic uniform/multicolor, disjoint figures in both orders, nested figures in both orientations, a crossing and its reversal, plus cubic clip, SourceCopy, pen and glyph consumers. Original native-recorded EMFs, direct/replay RGBA and native flattened points are retained. No earlier corpus was rerun.
Three explicit-path playback controls, revision 9adc067b41268448ed43159fd595fd44b5802cfc: the native writer had serialized flattened point arrays. These controls replace only the boundary with the original cubic or multiple-figure EmfPlusPath and update its flag and enclosing lengths. Colors, transforms and drawing records remain unchanged. Multicolor cubic and multiple-figure playback match their native-recorded equivalents byte-for-byte; uniform cubic differs by at most two channel units.

The reference receipt binds run/job/artifact hashes, original probe sources, substitutions and numeric profiles. Core fixtures bind original EMF and full 64 × 64 RGBA hashes. Glyph coverage uses a colored-ink property because Windows Arial and macOS font fallback do not guarantee identical outlines.

Boundary and interpolation behavior

For the measured cubic, GDI+ flattens the original seven points to 33 points. Recursive midpoint subdivision at chord/control flatness 0.25, followed by rounding to a 1/16 path-space grid, reproduces all 33 native points exactly. Explicit cubic playback agrees with this flattened representation. The renderer uses that general bounded subdivision, not an ellipse fitted to an arbitrary curve. Surrounding colors retain their ordinal assignment after flattening; unspecified entries become opaque white, consistent with the existing measured point-array profile. They are not resampled along the original cubic controls.

Closed figures contribute one ordered point array. A new figure does not create a separate gradient or a hole; crossings do not imply a polygon winding clip. The final covering center/edge fan owns a pixel. SourceCopy still uses independent recorded drawing geometry, so brush alpha and gradient coverage do not replace the command's geometric mask. The earlier rejection of intersecting edges and zero signed area prevented valid crossing brushes and is removed. Wholly collinear boundaries remain unsupported.

The existing Gouraud counter reflected negative startup progress with an absolute value. Three outer pixels on the new curved boundary exposed that error. A vertex exactly on a scanline retains the measured quantized seed; after stepping above a fractional vertex, negative progress stays at zero. This common endpoint-phase rule matches all seven new multicolor full frames and nine retained native phase/triangle/quad controls with exact coverage and maximum channel error one. These are numerical probes of the shipping shader functions against immutable Windows data, not decoder or application acceptance. Rejected unconditional-clamp and first-span experiments remain in ignored diagnostic evidence. No per-case coordinates, pixel substitutions or relaxed tolerances are used.

Implicit closure

The initial implementation inherited an explicit-close-bit requirement from the old bounded polygon profile. That was an unsupported validity assumption. Microsoft's open-figure fill contract treats an open figure as closed. A focused Windows replay, revision 9cfb66907a224c6fc743fd6b055727a4da7d465a, compares the exact earlier-red-paint cubic fixture with a counterpart differing only in the final CloseSubpath bit. Both succeed and their full RGBA frames are byte-identical. The original cubic already ends at its starting coordinate: this directly proves close-bit irrelevance, rather than independently measuring a distinct-endpoint closure.

The renderer accepts open line/cubic figures and new-figure adjacency through the same measured ordered fan, whose last point joins the first. General implicit closure follows that fan model and the documented fill contract. Separate open-multicolor and open-line fixtures retain the previously measured closed frames as explicit derived regressions; they are labeled as derivatives rather than new Windows pixel measurements. Normalizing the final flag in a private decoded copy also keeps an otherwise canonical open ellipse on its established analytic profile. Original source bytes and intermediate figure order remain. The old open negative fixture is replaced by a positive full-frame/source-byte check; the excessive-subdivision fixture still refuses the whole image.

Ownership, refusal and limits

The renderer still completes the whole decode before publishing an image. Malformed or excessive later boundaries cannot expose earlier painting as a successful partial result. Original file bytes remain the comparison/editor identity. Shared native image consumers retain their existing permission, cancellation, operation and retirement ownership.

Input and flattened boundaries each admit at most 4,096 points. Cubic subdivision allows depth 20 and 65,536 subdivision visits per boundary; flattened points also count toward the existing 1,048,576 aggregate decoded-point limit. Existing 16,777,216 boundary-work, 16,777,216 viewport-pixel and 67,108,864 aggregate raster/work limits remain. A Gouraud edge with zero truncated major-axis extent is still explicitly refused; this continuation does not invent subpixel colors. Wholly collinear boundaries are also refused. These bounds do not promise arbitrary devices, fonts, giant coordinates, signed sandbox acceptance, complete GDI+ raster parity or full application parity. No Wine implementation code was copied; the subdivision and shader changes are original code grounded in the specification and retained Windows observations.