Phase 8 #4 of REVIEWS/DART_PDF_VS_MAKEPAD_PDF_GAP_ANALYSIS.md
("Advanced colour"). Design and merge criteria in
REVIEWS/adr/0006-pdf-advanced-color.md.
The interpreter tracked only the *name* of the active colour space and
then passed sc/scn operands to the device as if they were already RGBA.
Every non-device space therefore rendered a confident wrong colour with
no error:
/Spot cs 1.0 scn full tint of a spot ink -> pure red
/Idx cs 3 scn palette entry 3 -> near-black
/Lab cs 50 0 0 scn mid gray -> white (clamped)
/DevN cs (5 inks) five colorants -> inks 5+ discarded
/ICCBased profile-defined colour -> profile discarded
DeviceCMYK also used the additive 1-c-k conversion, which crushes any
colour printed over black.
Three new modules in pdf-graphics:
- function.rs PDF functions, all four types. Type 4 runs on a bounded
interpreter: depth 32, 32768 tokens, stack 100, 100000
steps, and an unknown operator is an error rather than a
no-op that would leave a plausible wrong colour.
- icc.rs ICC matrix/TRC and gray kTRC profiles, applied exactly.
LUT-class profiles are reported as such and the caller
falls back to /Alternate; they are never pretended to be
matrix profiles.
- colorspace.rs All eleven families, converting through XYZ with
Bradford adaptation and a real sRGB transfer function.
Wiring:
- PdfDevice gains set_stroke_components/set_fill_components, so SC/SCN
reach the device as components of the active space instead of being
read positionally as RGBA.
- cs/CS now resets to the space's initial colour (table 74), which is
why golden/colors.txt gains a line.
- PdfPage::color_spaces carries /Resources /ColorSpace fully
dereferenced with streams decoded; a half-resolved space would make
every ICC profile, palette and type 0/4 transform silently fall back.
- A space that cannot be resolved keeps the previous colour and records
a typed ColorError. No colour is invented, and no error is swallowed.
Tests: 12 corpus fixtures under tests/corpus/color/, 14 acceptance
tests in pdf-document/tests/color.rs asserting numeric RGB (the broken
code produced a colour for every one of these; only the value was
wrong), plus unit tests per function type and per curve type. Two fuzz
targets added: eval_function and parse_colorspace.
TEST_TARGET=pdf 387 -> 447 passing, TEST_TARGET=pdf-ui 431 -> 491.
rustfmt and clippy -D warnings clean.
