SVG export: a gradient mesh patch is cut no finer than its colour changes

Each patch of a gradient mesh was cut into 8 x 8 flat quads for SVG export,
Object > Expand and the other outputs that cannot shade a mesh, whatever its
colours, so a patch of one colour became 64 identical pieces. Neighbouring
quads are now joined into square blocks wherever the colour changes by no
more than about one 8-bit step across the block; the block's outline runs
through its quads' corners, and a patch that folds over itself is not joined.

docs/file-format-parity.md

@@ -1,6 +1,6 @@
 # File format parity
 
-> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-31 · **Change:** minor (PDF import: knockout and isolated groups keep their flags after a group drawn straight onto its parent) · **Target:** Adobe Illustrator 2026 (30.x)
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-31 · **Change:** minor (SVG export and Expand: a gradient mesh patch is cut no finer than its colour changes) · **Target:** Adobe Illustrator 2026 (30.x)
 
 Every format Illustrator opens, places, saves or exports, against VectorCraft's format table (`FORMATS`,
 `OPEN_EXTS`, `PLACE_EXTS` in `crates/engine/src/cmd/fileio/formats.rs`). Illustrator's list comes from its public
@@ -132,6 +132,7 @@ the app's own editing copy of a file (an EPS after its `%%EOF`, a `.ai`'s `AIPri
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-31 | minor | SVG export (and Object › Expand, EPS, DXF, EMF and the other outputs that cut a gradient mesh into flat pieces): each patch was cut into 8 × 8 quads whatever its colours, so a patch of one colour became 64 identical pieces. Neighbouring quads are now joined into square blocks wherever the colour changes by no more than about one 8-bit step across the block, so a flat patch is one piece and a patch that shades strongly keeps all 64; a block's outline runs through its quads' corners, and a patch that folds over itself is not joined. A synthetic page of 400 meshes (6 × 6 patches, half flat) exports 468,000 pieces instead of 921,600 (35 MB instead of 66 MB), and resvg draws the two files identically. Tests `mesh_export` (crate `vectorcraft-svg`), `tests::live::mesh_expand_to_flat_pieces`; scores unchanged |
 | 2026-10-31 | minor | PDF import (and a `.ai`'s PDF part): a transparency group's knockout and isolate flags (`/K`, `/I`; ISO 32000-1, 11.4.6.3) come from the interpreter as it pushes the group. They were read from the file in order and matched to the groups pushed, but a group that adds nothing (full opacity, Normal, no mask, neither flag) is drawn straight onto its parent without being pushed, so every group after one lost its own flags and took another's; and a page drawing form groups more than 10,000 times failed to import (the list of their flags was capped), which it no longer does. A blend's steps written as a knockout group of falling opacity drew as solid dark shapes: a user's `.ai` with 143 such bubbles now draws them as light rings, as poppler does (its bubble area 4.9% → 1.2% of pixels off from poppler's render); 16 other users' PDFs with transparency groups (44 pages) draw the same. Test `tests::import_fidelity::knockout_groups_after_a_group_drawn_straight_keep_their_flag`; scores unchanged |
 | 2026-10-30 | minor | `.ai`/EPS editing data: a blend takes the transparency (opacity, blend mode, knockout; blends are written with knockout on) in the state block after its record, as a group takes the one after its end; it was left for the next object, so a blend's steps of falling opacity drew over each other instead of knocking each other out, and every such blend came in too dark (a user's file has 143, its bubbles came in as dark rings). Both a live blend and drawn steps kept as a group take it. Test `import::ai::tests::a_blends_transparency_follows_its_record`; checked locally against that file: it comes 1.3% → 0.6% nearer its page, though a mesh seen through a mesh-shaped opacity mask still keeps it just over the limit. When a blend is the layer's last object and the layer's own state block (`7 () XW`, then `LB`) follows, the state is the layer's and the blend keeps its own, as for meshes (#4748); scores unchanged |
 | 2026-10-31 | minor | PDF (and `.ai`) with Illustrator editing data saved with only some of its artboards: its pages are those artboards, while the editing data keeps them all, and the layers were compared with the first page on the first artboard, so a page of the second artboard came in as the PDF part, without its layers. With fewer pages than artboards, the first page is now taken to be the artboard of its size whose art draws most like it (up to 16 weighed), and the pages' type goes to that artboard and the ones after it. All artboards come in, as before. Test `import::tests_native::a_pdf_of_its_second_artboard_is_compared_on_that_artboard`; scores unchanged |