G2: Effect › Sketch › Chalk & Charcoal raster filter

Adds sketch.chalkCharcoal to the pixel-effect pipeline so Effect › Sketch exposes chalk highlights and charcoal strokes with public-doc-style parameters and tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

crates/effects/src/lib.rs

@@ -467,6 +467,13 @@ pub fn effect_catalog() -> Vec<EffectInfo> {
             "{amount: % 1..500 (50), radius: pt 0.1..250 (1; σ of the blur edges are found against), threshold: levels 0..255 (0; smaller differences are left alone)}",
             json!({"amount": 50.0, "radius": 1.0, "threshold": 0.0}),
         ),
+        r(
+            "sketch.chalkCharcoal",
+            "Chalk & Charcoal…",
+            SKETCH,
+            "{chalkArea: 0..20 (6; chalk in light areas), charcoalArea: 0..20 (6; charcoal in dark areas), strokePressure: 0..5 (2)} redraws the object with chalk highlights and charcoal strokes on white paper, keeping its coverage. Original visual approximation from public documentation; slider ranges and defaults are VectorCraft choices, not verified proprietary values.",
+            json!({"chalkArea": 6.0, "charcoalArea": 6.0, "strokePressure": 2.0}),
+        ),
         r(
             "sketch.halftonePattern",
             "Halftone Pattern…",

crates/effects/src/pixel/mod.rs

@@ -1,7 +1,8 @@
 //! Photoshop-style raster effects (Effect › Artistic › Cutout, Film Grain, Neon Glow and Poster Edges, Blur › Radial Blur and Smart Blur, Brush Strokes ›
 //! Accented Edges, Angled Strokes, Crosshatch, Dark Strokes, Ink Outlines, Spatter, Sprayed Strokes
 //! and Sumi-e, Distort › Diffuse Glow, Glass and Ocean Ripple, Pixelate › Color Halftone,
-//! Crystallize, Mezzotint and Pointillize, Sharpen › Unsharp Mask, Sketch › Halftone Pattern, Stylize ›
+//! Crystallize, Mezzotint and Pointillize, Sharpen › Unsharp Mask, Sketch › Chalk & Charcoal and
+//! Halftone Pattern, Stylize ›
 //! Glowing Edges, Texture
 //! › Craquelure, Grain, Mosaic Tiles, Patchwork, Stained Glass and Texturizer, and Video ›
 //! De-Interlace and NTSC Colors): filters over premultiplied RGBA8 pixels.
@@ -39,7 +40,7 @@ pub use sketch::{HALFTONE_TYPES, HalftonePattern};
 pub use texture::{GRAIN_TYPES, Grain, LIGHT_DIRECTIONS, Light, TEXTURES, Texture};
 
 /// The Photoshop-style effect ids (all raster effects, see [`crate::is_raster`]).
-pub const PIXEL_EFFECTS: [&str; 32] = [
+pub const PIXEL_EFFECTS: [&str; 33] = [
     "artistic.cutout",
     "artistic.filmGrain",
     "artistic.neonGlow",
@@ -62,6 +63,7 @@ pub const PIXEL_EFFECTS: [&str; 32] = [
     "pixelate.mezzotint",
     "pixelate.pointillize",
     "sharpen.unsharpMask",
+    "sketch.chalkCharcoal",
     "sketch.halftonePattern",
     "stylize.glowingEdges",
     "texture.craquelure",
@@ -139,6 +141,9 @@ pub enum PixelFx {
     /// Sharpen › Unsharp Mask: colours pushed away from a Gaussian blur of σ = `radius` by `amount`
     /// (1 = 100 %), where they differ from it by at least `threshold` levels.
     UnsharpMask { amount: f64, radius: f64, threshold: f64 },
+    /// Sketch › Chalk & Charcoal: chalk highlights in light areas and charcoal in dark ones;
+    /// `chalk` and `charcoal` (0..20) set how much, `pressure` (0..5) the stroke weight.
+    ChalkCharcoal { chalk: f64, charcoal: f64, pressure: f64 },
     /// Sketch › Halftone Pattern: black ink on white paper through a `kind` screen of cells `size`
     /// (1..12) apart, its edges as hard as `contrast` (0..50) says.
     HalftonePattern { size: f64, contrast: f64, kind: HalftonePattern },
@@ -311,6 +316,11 @@ pub(crate) fn parse(id: &str, p: &Value) -> Option<PixelFx> {
             radius: num(p, "radius", 1.0).clamp(0.1, 250.0),
             threshold: num(p, "threshold", 0.0).clamp(0.0, 255.0),
         },
+        "sketch.chalkCharcoal" => PixelFx::ChalkCharcoal {
+            chalk: num(p, "chalkArea", 6.0).clamp(0.0, 20.0),
+            charcoal: num(p, "charcoalArea", 6.0).clamp(0.0, 20.0),
+            pressure: num(p, "strokePressure", 2.0).clamp(0.0, 5.0),
+        },
         "sketch.halftonePattern" => PixelFx::HalftonePattern {
             size: num(p, "size", 1.0).clamp(1.0, 12.0),
             contrast: num(p, "contrast", 5.0).clamp(0.0, 50.0),
@@ -392,7 +402,7 @@ impl PixelFx {
             // Content shifted outwards reaches past the bounds by as much as the shift.
             PixelFx::Glass { distortion, .. } => distort::glass_shift(distortion),
             PixelFx::OceanRipple { size, magnitude } => distort::ripple_shift(size, magnitude),
-            PixelFx::UnsharpMask { .. } | PixelFx::HalftonePattern { .. } => 0.0,
+            PixelFx::UnsharpMask { .. } | PixelFx::ChalkCharcoal { .. } | PixelFx::HalftonePattern { .. } => 0.0,
             PixelFx::GlowingEdges { width, smoothness, .. } => width.max(smoothness * 3.0),
             PixelFx::FilmGrain { .. }
             | PixelFx::Cutout { .. }
@@ -439,6 +449,7 @@ impl PixelFx {
             // The cells around the pixel's, and the cells around theirs.
             PixelFx::ColorHalftone { max_radius, .. } => Some(3.0 * std::f64::consts::SQRT_2 * max_radius),
             PixelFx::Crystallize { cell } => Some(1.5 * cell),
+            PixelFx::ChalkCharcoal { .. } => Some(sketch::CHALK_CHARCOAL_REACH),
             PixelFx::FilmGrain { .. } | PixelFx::Mezzotint { .. } | PixelFx::HalftonePattern { .. } => Some(0.0),
             // Cutout's palette comes from the whole object.
             PixelFx::Cutout { .. } => None,
@@ -493,6 +504,7 @@ impl PixelFx {
             }
             PixelFx::OceanRipple { size, magnitude } => distort::ocean_ripple(px, w, h, space, size, magnitude),
             PixelFx::UnsharpMask { amount, radius, threshold } => sharpen::unsharp(px, w, h, amount, to_px(radius), threshold),
+            PixelFx::ChalkCharcoal { chalk, charcoal, pressure } => sketch::chalk_charcoal(px, w, h, space, chalk, charcoal, pressure),
             PixelFx::HalftonePattern { size, contrast, kind } => sketch::halftone_pattern(px, w, h, space, size, contrast, kind),
             PixelFx::GlowingEdges { width, brightness, smoothness } => edges::glow(px, w, h, to_px(width), brightness, to_px(smoothness)),
             PixelFx::ColorHalftone { max_radius, angles } => pixelate::color_halftone(px, w, h, space, max_radius, angles),

crates/effects/src/pixel/sketch.rs

@@ -1,12 +1,37 @@
-//! Effect › Sketch › Halftone Pattern. Original filter built from public behaviour documentation:
+//! Effect › Sketch (Chalk & Charcoal, Halftone Pattern). Original filters built from public
+//! behaviour documentation:
 //! <https://helpx.adobe.com/illustrator/using/summary-effects.html> (Sketch effects redraw in
-//! black and white; Halftone Pattern simulates a halftone screen while keeping the range of tones)
-//! and <https://helpx.adobe.com/illustrator/using/effects.html> (only Size depends on the raster
-//! resolution). A visual approximation, not a reproduction of a proprietary algorithm.
+//! black and white) and the public Photoshop Elements Artistic filters guide. Visual
+//! approximations, not proprietary reproductions.
 
-use super::pixelate::Place;
-use super::texture::{luma, premultiply, straight};
-use super::{PixelSpace, pick};
+use std::f64::consts::TAU;
+
+use super::edges::sobel;
+use super::pixelate::{Place, value_noise};
+use super::texture::{Tones, luma, premultiply, straight};
+use super::{PixelSpace, blur_plane, pick};
+
+const SALT_CHALK: u64 = 216;
+const EDGE_SOFT: f64 = 0.8;
+const TONE_SOFT: f64 = 1.0;
+
+/// How far (document units) Chalk & Charcoal samples softened tones and edges.
+pub(super) const CHALK_CHARCOAL_REACH: f64 = 3.0 * TONE_SOFT + 1.0 + 3.0 * EDGE_SOFT;
+
+fn ramp(t: f64) -> f64 {
+    t.clamp(0.0, 1.0)
+}
+
+fn tone_edges(px: &[[u8; 4]], w: usize, h: usize, place: &Place, sigma: f64) -> Vec<f32> {
+    let mut tone: Vec<f32> = px.iter().map(|p| luma(straight(*p)) * f32::from(p[3]) / 255.0).collect();
+    let mut cover: Vec<f32> = px.iter().map(|p| f32::from(p[3]) / 255.0).collect();
+    let s = sigma / place.px;
+    blur_plane(&mut tone, w, h, s);
+    blur_plane(&mut cover, w, h, s);
+    let norm = (s.max(0.8) * TAU.sqrt() / 8.0) as f32;
+    let norm = if norm.is_finite() { norm } else { 0.0 };
+    sobel(&tone, w, h).iter().zip(sobel(&cover, w, h)).map(|(t, c)| t.max(c) * norm).collect()
+}
 
 /// Halftone Pattern's screens, in its Pattern Type menu's order: (label, parameter value).
 pub const HALFTONE_TYPES: [(&str, &str); 3] = [("Circle", "circle"), ("Dot", "dot"), ("Line", "line")];
@@ -69,3 +94,46 @@ pub(super) fn halftone_pattern(px: &mut [[u8; 4]], w: usize, h: usize, space: &P
         *p = premultiply([(1.0 - ink) as f32; 3], f32::from(p[3]) / 255.0);
     });
 }
+
+/// Chalk & Charcoal: light areas get chalky highlights and dark areas charcoal strokes and grain;
+/// `chalk` and `charcoal` (0..20) set how strongly, `pressure` (0..5) the stroke weight. Black
+/// chalk and charcoal on white paper, coverage kept.
+pub(super) fn chalk_charcoal(px: &mut [[u8; 4]], w: usize, h: usize, space: &PixelSpace, chalk: f64, charcoal: f64, pressure: f64) {
+    if !(chalk.is_finite() && charcoal.is_finite() && pressure.is_finite()) {
+        return;
+    }
+    let scale = (pressure.clamp(0.0, 5.0) / 5.0).clamp(0.0, 1.0);
+    let chalk_amt = (0.05 * chalk.clamp(0.0, 20.0) * scale).clamp(0.0, 1.0);
+    let charcoal_amt = (0.05 * charcoal.clamp(0.0, 20.0) * scale).clamp(0.0, 1.0);
+    if chalk_amt <= 0.0 && charcoal_amt <= 0.0 {
+        return;
+    }
+    let Some(place) = Place::new(space, w, h) else { return };
+    let tones = Tones::new(px, w, h, TONE_SOFT / place.px);
+    let edges = tone_edges(px, w, h, &place, EDGE_SOFT);
+    place.each(px, |x, y, p| {
+        if p[3] == 0 {
+            return;
+        }
+        let q = place.at(x, y);
+        let tone = tones.get(x, y);
+        let dark = (1.0 - tone).clamp(0.0, 1.0);
+        let light = tone.clamp(0.0, 1.0);
+        let edge = f64::from(edges.get(y * w + x).copied().unwrap_or(0.0));
+        let charcoal_stroke = value_noise(SALT_CHALK + 1, q.x * 1.1, q.y * 0.12);
+        let charcoal_grain = value_noise(SALT_CHALK, q.x * 0.35, q.y * 0.35);
+        let charcoal_mask = ramp((dark - 0.3) / 0.22)
+            * charcoal_amt
+            * (0.35 + 0.65 * edge)
+            * (0.45 + 0.55 * ramp(charcoal_stroke * 2.2 - 0.55))
+            * (0.6 + 0.4 * charcoal_grain);
+        let chalk_grain = value_noise(SALT_CHALK + 2, q.x * 0.45 + 7.0, q.y * 0.45);
+        let chalk_mask = ramp((light - 0.5) / 0.22) * chalk_amt * (0.55 + 0.45 * chalk_grain);
+        let down = (0.9 * charcoal_mask).clamp(0.0, 1.0) as f32;
+        let up = (0.8 * chalk_mask).clamp(0.0, 1.0) as f32;
+        let mut grey = f32::from(luma(straight(*p)));
+        grey *= 1.0 - down;
+        grey += (1.0 - grey) * up;
+        *p = premultiply([grey, grey, grey], f32::from(p[3]) / 255.0);
+    });
+}

crates/effects/src/pixel/tests.rs

@@ -1998,6 +1998,50 @@ fn brush_strokes_follow_the_object_at_any_resolution() {
     }
 }
 
+/// Chalk & Charcoal of `p` over `w` × `h` pixels of `src`, laid out by `s`.
+fn chalk_charcoal(p: serde_json::Value, src: &[u8], w: usize, h: usize, s: &PixelSpace) -> Vec<u8> {
+    let mut out = src.to_vec();
+    fx("sketch.chalkCharcoal", p).apply(&mut out, w, h, s);
+    out
+}
+
+#[test]
+fn chalk_charcoal_params_take_defaults_and_stay_in_range() {
+    assert_eq!(
+        fx("sketch.chalkCharcoal", json!({})),
+        PixelFx::ChalkCharcoal { chalk: 6.0, charcoal: 6.0, pressure: 2.0 }
+    );
+    assert_eq!(
+        fx("sketch.chalkCharcoal", json!({"chalkArea": 1e9, "charcoalArea": -2, "strokePressure": 99})),
+        PixelFx::ChalkCharcoal { chalk: 20.0, charcoal: 0.0, pressure: 5.0 }
+    );
+    let doc = crate::effect_info("sketch.chalkCharcoal").unwrap().params;
+    assert!(doc.contains("chalkArea") && doc.contains("charcoalArea") && doc.contains("strokePressure"), "{doc}");
+    let f = fx("sketch.chalkCharcoal", json!({"strokePressure": 5}));
+    assert_eq!(f.outset(Rect::new(0.0, 0.0, 100.0, 50.0)), 0.0);
+    assert!(f.reach().unwrap() > 0.0);
+}
+
+#[test]
+fn chalk_charcoal_draws_in_black_and_white_only() {
+    let (w, h) = (48, 48);
+    let src = image(w, h, |x, y| {
+        let c = [[230u8, 20, 20], [20, 200, 40], [30, 60, 220], [240, 220, 30]][(x / 12) % 4];
+        let a: u16 = if y < 24 { 255 } else { 128 };
+        [c[0], c[1], c[2]].map(|v| (u16::from(v) * a / 255) as u8).into_iter().chain([a as u8]).collect::<Vec<_>>().try_into().unwrap()
+    });
+    let out = chalk_charcoal(json!({"chalkArea": 12, "charcoalArea": 12, "strokePressure": 4}), &src, w, h, &space(w, h));
+    for (p, q) in out.as_chunks::<4>().0.iter().zip(src.as_chunks::<4>().0) {
+        assert_eq!(p[3], q[3], "coverage kept");
+        if p[3] == 0 {
+            continue;
+        }
+        assert_eq!(p[0], p[1]);
+        assert_eq!(p[1], p[2]);
+    }
+    assert_ne!(out, src);
+}
+
 /// Halftone Pattern of `p` over `w` × `h` pixels of `src`, laid out by `s`.
 fn halftone(p: serde_json::Value, src: &[u8], w: usize, h: usize, s: &PixelSpace) -> Vec<u8> {
     let mut out = src.to_vec();

crates/ui-egui/src/tests_labels.rs

@@ -171,18 +171,19 @@ fn effect_menu_lists_the_texture_filters_between_sharpen_and_video() {
     assert!(at("Sharpen") < at("Texture") && at("Texture") < at("Video"));
 }
 
-/// Effect › Sketch, between Sharpen and the raster Stylize: Halftone Pattern opens its dialog.
+/// Effect › Sketch, between Sharpen and the raster Stylize: Chalk & Charcoal and Halftone Pattern open their dialogs.
 #[test]
 fn effect_menu_lists_the_sketch_filters_between_sharpen_and_stylize() {
     let app = app();
     let entries = menus::menu_entries(&app);
     let sketch: Vec<_> = entries.iter().filter(|e| e.path == ["Effect", "Sketch"]).collect();
     let labels: Vec<&str> = sketch.iter().map(|e| e.label.as_str()).collect();
-    assert_eq!(labels, ["Halftone Pattern…"]);
+    assert_eq!(labels, ["Chalk & Charcoal…", "Halftone Pattern…"]);
     assert_eq!(sketch[0].command.as_deref(), Some("effect.dialog"));
-    assert_eq!(sketch[0].params, json!({"effect": "sketch.halftonePattern"}));
+    assert_eq!(sketch[0].params, json!({"effect": "sketch.chalkCharcoal"}));
+    assert_eq!(sketch[1].params, json!({"effect": "sketch.halftonePattern"}));
     let at = |label: &str| entries.iter().position(|e| e.path[0] == "Effect" && e.label == label).unwrap();
-    assert!(at("Unsharp Mask…") < at("Halftone Pattern…") && at("Halftone Pattern…") < at("Glowing Edges…"));
+    assert!(at("Unsharp Mask…") < at("Chalk & Charcoal…") && at("Chalk & Charcoal…") < at("Halftone Pattern…") && at("Halftone Pattern…") < at("Glowing Edges…"));
 }
 
 /// Effect › Stylize under Raster Effects, between Sharpen and Texture: Glowing Edges opens its