360 lines
15 KiB
Rust
360 lines
15 KiB
Rust
//! Blending in CMYK documents.
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//!
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//! In a CMYK document blend modes and opacity composite inks, not screen colours: Multiply of cyan
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//! over magenta prints both inks (blue, C100 M100 through the CMYK profile), where screen RGB would
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//! give the product of the two display colours. The renderer composites additive values, so a CMYK
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//! document that shows transparency is drawn twice, once per ink plane
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//! ([`vectorcraft_color::blend::cmyk_planes`]): every colour painted as its complemented C, M and
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//! Y ([`Ink::Cmy`]), then as its complemented K, a grey ([`Ink::K`]). Blend modes, opacity,
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//! groups, knockouts and effects composite the planes exactly as they composite RGB, which is CMYK
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//! blending. [`compose`] reads each pixel's inks back and shows them through the working CMYK
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//! profile (a cached 4-D lookup table). Opacity masks keep taking their luminance from screen
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//! colours; RGB colours and placed images are separated into the working CMYK space first.
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//!
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//! RGB documents, and CMYK documents without transparency, draw screen colours ([`Ink::Display`]).
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use std::cell::RefCell;
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use std::collections::HashMap;
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use std::sync::{Arc, Mutex};
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use vectorcraft_color::Color;
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use vectorcraft_color::blend::{cmyk_planes, planes_cmyk};
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use vectorcraft_color::cms::{self, Cms, CmykLut, ProofLut, lab};
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use vectorcraft_doc::cmyk::Inks;
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use vectorcraft_doc::{ColorMode, Document, ImageBlob};
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use vello_cpu::Pixmap;
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use vello_cpu::color::PremulRgba8;
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use vello_cpu::peniko;
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use crate::{RenderOptions, Renderer};
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/// What a frame paints for colours.
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#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
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pub(crate) enum Ink {
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/// Screen colours.
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#[default]
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Display,
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/// The complemented C, M and Y inks.
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Cmy,
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/// The complemented K ink, as a grey.
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K,
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}
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impl Ink {
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/// The three values painted for colour `c`.
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pub(crate) fn rgb(self, c: &Color) -> [f32; 3] {
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match self {
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Ink::Display => c.to_rgb(),
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_ => self.plane(inks(c)),
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}
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}
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/// [`Self::rgb`] as a paint, at `alpha`.
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pub(crate) fn color(self, c: &Color, alpha: f32) -> peniko::Color {
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let [r, g, b] = self.rgb(c);
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peniko::Color::from_rgba8(q(r), q(g), q(b), q(alpha))
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}
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/// A fixed screen colour (pasteboard, guides, tile edges) as a paint.
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pub(crate) fn fixed(self, rgba: [u8; 4]) -> peniko::Color {
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let [r, g, b, a] = self.fixed8(rgba);
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peniko::Color::from_rgba8(r, g, b, a)
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}
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fn fixed8(self, [r, g, b, a]: [u8; 4]) -> [u8; 4] {
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match self {
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Ink::Display => [r, g, b, a],
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_ => {
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let lab = lab::srgb_to_lab([r, g, b].map(|v| v as f32 / 255.0));
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let [r, g, b] = self.plane(inks(&Color::Lab { l: lab.l, a: lab.a, b: lab.b })).map(q);
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[r, g, b, a]
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}
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}
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}
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fn plane(self, inks: [f32; 4]) -> [f32; 3] {
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cmyk_planes(inks)[(self == Ink::K) as usize]
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}
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}
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fn q(v: f32) -> u8 {
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(v.clamp(0.0, 1.0) * 255.0).round() as u8
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}
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/// Whether `doc` is drawn by ink planes: a CMYK document that shows transparency, unless drawn
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/// in Outline view or Separations Preview (which paints plates).
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pub(crate) fn blends_in_cmyk(doc: &Document, opts: &RenderOptions) -> bool {
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doc.color_mode == ColorMode::Cmyk
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&& !opts.outline
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&& opts.proof.as_ref().is_none_or(|p| p.separations.is_none())
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&& (doc.layers.iter().any(|l| l.shows_transparency())
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|| doc.symbols.iter().any(|s| s.art.shows_transparency())
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|| doc.patterns.iter().any(|p| p.art.iter().any(|a| a.shows_transparency())))
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}
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/// The inks of `c` in the working CMYK space: CMYK as it is, grey as black ink, RGB and Lab
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/// separated with the colour settings' intent (cached: separating searches the profile).
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fn inks(c: &Color) -> [f32; 4] {
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let key = match *c {
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Color::Cmyk { c, m, y, k } => return [c, m, y, k],
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Color::Gray { k } => return [0.0, 0.0, 0.0, k],
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Color::Rgb { r, g, b } => [0, r.to_bits(), g.to_bits(), b.to_bits()],
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Color::Lab { l, a, b } => [1, l.to_bits(), a.to_bits(), b.to_bits()],
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};
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let cms = cms::active();
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SEPARATED.with(|s| {
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let (owner, seen) = &mut *s.borrow_mut();
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if !owner.as_ref().is_some_and(|o| Arc::ptr_eq(o, &cms)) || seen.len() >= 4096 {
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seen.clear();
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*owner = Some(cms.clone());
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}
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*seen.entry(key).or_insert_with(|| cms.to_cmyk(c, cms.settings().intent))
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})
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}
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/// Separated colours, for the colour settings they were separated with.
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type Separated = (Option<Arc<Cms>>, HashMap<[u32; 4], [f32; 4]>);
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thread_local! {
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static SEPARATED: RefCell<Separated> = RefCell::default();
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}
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/// Inks → display sRGB through the working CMYK profile: a 17⁴ lookup table of XYZ, interpolated
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/// quadrilinearly (inks mix close to linearly in light, and out-of-gamut colours are clipped
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/// after interpolating, not before).
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pub(crate) struct InkLut(CmykLut);
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impl InkLut {
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fn build(cms: &Cms) -> Self {
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Self(CmykLut::build(|inks| {
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let [x, y, z] = lab::lab_to_xyz(cms.cmyk_to_lab(inks));
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[x, y, z, 0.0]
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}))
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}
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fn apply(&self, inks: [f32; 4]) -> [f32; 3] {
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let [x, y, z, _] = self.0.apply(inks);
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lab::xyz_to_srgb([x, y, z])
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}
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}
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/// Placed images as painted with [`Ink::Cmy`] and [`Ink::K`], per image key, with the tables they
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/// were separated by.
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pub(crate) type InkImages = HashMap<String, (Arc<[ProofLut; 2]>, [Arc<Pixmap>; 2])>;
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/// A table built for the colour settings it was built with.
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type Cached<T> = Mutex<Option<(Arc<Cms>, Arc<T>)>>;
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static DISPLAY: Cached<InkLut> = Mutex::new(None);
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/// Screen colours → [`Ink::Cmy`] and [`Ink::K`] values (placed images).
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static SEPARATE: Cached<[ProofLut; 2]> = Mutex::new(None);
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/// The table in `slot` for the active colour settings, built by `build` when they changed.
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fn cached<T>(slot: &Cached<T>, build: impl FnOnce(&Cms) -> T) -> Arc<T> {
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let cms = cms::active();
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let mut s = slot.lock().unwrap_or_else(|e| e.into_inner());
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match &*s {
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Some((owner, t)) if Arc::ptr_eq(owner, &cms) => t.clone(),
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_ => {
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let t = Arc::new(build(&cms));
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*s = Some((cms, t.clone()));
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t
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}
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}
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}
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/// The picture of a CMYK document from its ink planes (premultiplied RGBA8 drawn with
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/// [`Ink::Cmy`] and [`Ink::K`]): each pixel's inks shown through the working CMYK profile. Where
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/// only the frame's `background` shows it keeps its exact screen colour.
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pub(crate) fn compose(cmy: &[u8], k: &[u8], background: Option<[u8; 4]>) -> Vec<u8> {
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let lut = cached(&DISPLAY, InkLut::build);
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let bg = background.map(|b| (Ink::Cmy.fixed8(b), Ink::K.fixed8(b), b));
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let mut out = Vec::with_capacity(cmy.len());
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// Runs of one colour convert once.
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let mut last: Option<([u8; 8], [u8; 4])> = None;
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for (p, q) in cmy.as_chunks::<4>().0.iter().zip(k.as_chunks::<4>().0) {
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let key = [p[0], p[1], p[2], p[3], q[0], q[1], q[2], q[3]];
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let px = match (&last, &bg) {
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_ if p[3] == 0 => [0; 4],
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(Some((k0, v)), _) if *k0 == key => *v,
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(_, Some((bc, bk, b))) if p == bc && q == bk => *b,
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_ => {
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let un = |v: u8, a: u8| if a == 0 { 1.0 } else { (v as f32 / a as f32).min(1.0) };
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let a = p[3];
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let rgb = lut.apply(planes_cmyk([un(p[0], a), un(p[1], a), un(p[2], a)], un(q[0], q[3])));
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let pm = |v: f32| (v.clamp(0.0, 1.0) * a as f32).round() as u8;
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let v = [pm(rgb[0]), pm(rgb[1]), pm(rgb[2]), a];
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last = Some((key, v));
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v
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}
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};
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out.extend_from_slice(&px);
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}
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out
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}
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/// Each pixel's ink amounts (C, M, Y, K bytes, 0 = no ink) from its ink planes (premultiplied
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/// RGBA8 drawn with [`Ink::Cmy`] and [`Ink::K`]): a plane holds the complement of its inks, so
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/// the ink is coverage minus plane value (partly covered pixels carry that much ink).
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pub(crate) fn amounts(cmy: &[u8], k: &[u8]) -> Vec<u8> {
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cmy.as_chunks::<4>()
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.0
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.iter()
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.zip(k.as_chunks::<4>().0)
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.flat_map(|(p, q)| [p[3].saturating_sub(p[0]), p[3].saturating_sub(p[1]), p[3].saturating_sub(p[2]), q[3].saturating_sub(q[0])])
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.collect()
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}
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/// CMYK images as shown, per image key, with the table they were shown through.
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pub(crate) type CmykImages = HashMap<String, (Arc<InkLut>, Arc<Pixmap>)>;
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/// Ink amounts `inks` shown through `lut` (opaque).
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fn inks_pixmap(inks: &Inks, lut: &InkLut) -> Option<Pixmap> {
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let (w, h) = (u16::try_from(inks.width).ok()?, u16::try_from(inks.height).ok()?);
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// Runs of one colour convert once.
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let mut last: Option<([u8; 4], PremulRgba8)> = None;
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let data = inks
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.data
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.as_chunks::<4>()
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.0
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.iter()
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.map(|p| match last {
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Some((k, v)) if k == *p => v,
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_ => {
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let [r, g, b] = lut.apply(p.map(|v| v as f32 / 255.0)).map(q);
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let v = PremulRgba8 { r, g, b, a: 255 };
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last = Some((*p, v));
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v
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}
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})
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.collect();
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Some(Pixmap::from_parts(data, w, h))
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}
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impl Renderer {
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/// The pixels of CMYK image `blob` (cached as `cache_key`): its inks shown through the working
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/// CMYK profile, as CMYK colours are, again when the colour settings change. `None` for
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/// other images.
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pub(crate) fn cmyk_image(&mut self, blob: &ImageBlob, cache_key: &str) -> Option<Arc<Pixmap>> {
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// Other images are cached as they are once decoded: only CMYK ones come here again.
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let shown = self.cmyk_images.get(cache_key).cloned();
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if shown.is_none() && !blob.is_cmyk() {
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return None;
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}
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let lut = cached(&DISPLAY, InkLut::build);
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if let Some((owner, pm)) = shown
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&& Arc::ptr_eq(&owner, &lut)
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{
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return Some(pm);
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}
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let pm = Arc::new(inks_pixmap(&blob.cmyk()?, &lut)?);
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self.cmyk_images.insert(cache_key.to_string(), (lut, pm.clone()));
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Some(pm)
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}
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/// Placed image `key` (decoded as `pm`, from `blob`) as painted with `ink`, cached.
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pub(crate) fn ink_image(&mut self, key: &str, pm: &Arc<Pixmap>, ink: Ink, blob: Option<&ImageBlob>) -> Arc<Pixmap> {
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if ink == Ink::Display {
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return pm.clone();
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}
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let luts = cached(&SEPARATE, |cms| {
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let intent = cms.settings().intent;
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[Ink::Cmy, Ink::K].map(|ink| ProofLut::build(|rgb| ink.plane(cms.srgb_to_cmyk(rgb, intent))))
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});
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let at = (ink == Ink::K) as usize;
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if let Some((owner, planes)) = self.ink_images.get(key)
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&& Arc::ptr_eq(owner, &luts)
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{
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return planes[at].clone();
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}
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// CMYK images paint their own inks; the others are separated.
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let size = (pm.width() as u32, pm.height() as u32);
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let inks = blob.filter(|_| self.cmyk_images.contains_key(key)).and_then(ImageBlob::cmyk).filter(|i| (i.width, i.height) == size);
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let planes = [Ink::Cmy, Ink::K].map(|plane| {
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let mut out = Pixmap::new(pm.width(), pm.height());
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if let Some(inks) = &inks {
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for (o, p) in out.data_mut().iter_mut().zip(inks.data.as_chunks::<4>().0) {
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let [r, g, b] = plane.plane(p.map(|v| v as f32 / 255.0)).map(q);
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*o = PremulRgba8 { r, g, b, a: 255 };
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}
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return Arc::new(out);
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}
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let lut = &luts[(plane == Ink::K) as usize];
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for (o, s) in out.data_mut().iter_mut().zip(pm.data()) {
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let a = s.a;
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if a == 0 {
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continue;
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}
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let un = |v: u8| (v as f32 / a as f32).min(1.0);
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let [r, g, b] = lut.apply([un(s.r), un(s.g), un(s.b)]).map(|v| (v.clamp(0.0, 1.0) * a as f32).round() as u8);
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*o = PremulRgba8 { r, g, b, a };
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}
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Arc::new(out)
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});
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let out = planes[at].clone();
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self.ink_images.insert(key.to_string(), (luts, planes));
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out
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn the_ink_table_matches_the_profile() {
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let cms = cms::active();
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let lut = InkLut::build(&cms);
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let mut worst = 0.0f32;
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// Between the grid points (where interpolation errs most) and on them.
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for i in 0..=20 {
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for j in 0..=20 {
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let inks = [i as f32 / 20.0, j as f32 / 20.0, ((i * 7 + j * 3) % 21) as f32 / 20.0, ((i + j * 5) % 21) as f32 / 20.0];
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let (a, b) = (lut.apply(inks), cms.cmyk_to_srgb(inks, false));
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worst = worst.max((0..3).map(|c| (a[c] - b[c]).abs()).fold(0.0, f32::max));
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}
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}
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// Within two 8-bit levels: far below a visible difference.
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assert!(worst * 255.0 < 2.5, "worst error {} levels", worst * 255.0);
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}
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#[test]
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fn cmyk_images_show_through_the_profile_and_paint_their_own_inks() {
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use vectorcraft_color::Paint;
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use vectorcraft_doc::{Appearance, ImageObject, Node, NodeKind};
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use vectorcraft_geom::{Affine, Rect, shapes};
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let ink = [0u8, 102, 255, 25];
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let mut d = Document::new_with_mode(20.0, 10.0, ColorMode::Cmyk);
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d.images.insert("img".into(), ImageBlob::cmyk_tiff(&Inks::new(2, 2, ink.repeat(4)).unwrap()).unwrap());
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let l = d.layers[0].id;
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let im = ImageObject { key: "img".into(), width: 2, height: 2, xf: Affine::scale(5.0), link: None, placement: Default::default() };
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let n = Node::new(d.alloc_id(), NodeKind::Image(im));
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d.insert(Some(l), 0, n).unwrap();
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// The same inks as a fill beside it.
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let fill = Color::cmyk(0.0, 0.4, 1.0, 25.0 / 255.0);
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let n =
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Node::path(d.alloc_id(), shapes::rectangle(Rect::new(10.0, 0.0, 20.0, 10.0)), Appearance::basic(Paint::solid(fill), Paint::None, 0.0));
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d.insert(Some(l), 1, n).unwrap();
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let mut r = Renderer::new();
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let region = Rect::new(0.0, 0.0, 20.0, 10.0);
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let shown = r.render_region(&d, region, 1.0, true).pixels;
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let at = |px: &[u8], x: usize| px[(5 * 20 + x) * 4..][..4].to_vec();
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let (image, fill) = (at(&shown, 5), at(&shown, 15));
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assert!(image.iter().zip(&fill).all(|(a, b)| a.abs_diff(*b) <= 2), "{image:?} vs {fill:?}");
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// CMYK exports draw ink amounts: the image's own.
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let inks = r.render_region_inks(&d, region, 1.0, &RenderOptions::default());
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assert!(at(&inks, 5).iter().zip(ink).all(|(a, b)| a.abs_diff(b) <= 1), "{:?}", at(&inks, 5));
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}
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#[test]
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fn fixed_colours_and_paper() {
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// White is paper on both planes; the display plane keeps screen colours exactly.
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assert_eq!(Ink::Cmy.fixed8([255; 4]), [255; 4]);
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assert_eq!(Ink::K.fixed8([255; 4]), [255; 4]);
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assert_eq!(Ink::Display.fixed8([12, 34, 56, 78]), [12, 34, 56, 78]);
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assert_eq!(Ink::K.rgb(&Color::gray(0.25)), [0.75; 3]);
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assert_eq!(Ink::Cmy.rgb(&Color::cmyk(0.1, 0.2, 0.3, 0.4)), [0.9, 0.8, 0.7]);
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}
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}
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