PDF stage 4.9: axial & radial shadings (types 2/3)#573
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Render axial (type 2) and radial (type 3) shadings as SVG gradients, both
via the `sh` operator and via `/PatternType 2` shading patterns selected by
`scn`.
- `pdf_shading.{hpp,cpp}`: `parse_shading` resolves a `/Shading` dictionary,
pre-sampling its tint `/Function` across `/Domain` into 32 sRGB colour stops
(no function evaluator needed at render time). Types other than 2/3 and
malformed shadings return null; `/Extend`, `/Background` and `/BBox` are
parsed.
- Parser: `parse_resources` now builds the `/Shading` and `/Pattern` resource
tables (after `/ColorSpace`, so named colour spaces resolve). A shading
pattern resolves its `/Shading`; a tiling pattern is recognized (rendered in
4.10). `GraphicsState::Color` carries the selected `/Pattern` name.
- Extractor: `scn` records the pattern name; `paint_path` resolves a shading
pattern to `PathElement::fill_shading` + the pattern `/Matrix`; the `sh`
operator emits a `ShadingElement` flooding the current clip.
- HTML: a `GradientRegistry` emits `<linearGradient>`/`<radialGradient>` defs
with `gradientUnits="userSpaceOnUse"`; a shading-pattern fill paints the path
through `fill="url(#…)"`, and `sh` paints a clipped `<rect>`. `/Extend` is
approximated by SVG's `pad` spread.
Tests: shading parsing (axial/radial, domain/extend, background, unsupported
type, short coords, bad function) and extractor wiring (shading-pattern fill,
unknown pattern, `sh` element, unknown shading).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
…otes
Tightening from PR review, no behaviour change (197 PDF tests still green):
- Add `as_reals(const Object&)` to `pdf_object`, collapsing the repeated
"array `Object` -> vector<double>" loops in `image_decode`, the colour-key
`/Mask` branch, the inline-image `/Decode`, and the shading `read_numbers`.
- Add a file-local `bind_parser_io` template in the parser to bind the shared
`resolve`/`load_stream` hooks of every typed context (colour space, function,
shading), replacing four identical lambda pairs.
- Make the deferred shading features visible: `Shading::{extend,background,bbox}`
are parsed but not yet honoured by the renderer (it always uses SVG `pad`
spread). Documented on the `Shading` struct, the `GradientRegistry`, and
`pdf/AGENTS.md`.
- Note the `Resources::shading` (shared_ptr) vs `Resources::pattern` (Element*)
ownership asymmetry, and why only the gradient transform's translation is
rounded. Reflow two clang-format comment artifacts.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Uqx1dUpDUykRxui8FYwxvM
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🤖 Generated with Claude Code
Stage 4.9 of the PDF→HTML pipeline: render axial (type 2) and radial (type 3) shadings as SVG gradients, both via the
shoperator and via/PatternType 2shading patterns selected byscn. Stacked on #572 (4.8); targetspdf-stage-4.8.What
pdf_shading.{hpp,cpp}—parse_shadingresolves a/Shadingdictionary and pre-samples its tint/Functionacross/Domaininto 32 sRGB colour stops, so the renderer needs no function evaluator. Shading types other than 2/3 and malformed shadings return null;/Extend,/Backgroundand/BBoxare parsed.parse_resourcesnow builds the/Shadingand/Patternresource tables (after/ColorSpace, so a named colour space resolves). A shading pattern resolves its/Shading; a tiling pattern is recognized and deferred to 4.10.GraphicsState::Colorcarries the/Patternname selected byscn.scnrecords the pattern name;paint_pathresolves a shading pattern toPathElement::fill_shadingplus the pattern/Matrix; theshoperator emits aShadingElementflooding the current clip.GradientRegistryemits<linearGradient>/<radialGradient>defs withgradientUnits="userSpaceOnUse"; a shading-pattern fill paints the path throughfill="url(#…)", andshpaints a clipped<rect>./Extendis approximated by SVG'spadspread.Tests
PdfShading: axial/radial parsing, domain/extend, background, unsupported type, short coords, bad function → null.PdfPageExtractor: shading-pattern fill resolvesfill_shading+ matrix, unknown pattern leaves a plain fill,shemits aShadingElementat the CTM, unknown shading emits nothing.All 197 PDF tests pass; full suite green.
Notes
/PatternType 1, next in 4.10) are out of scope.