M14.4: as_chunks for the pixel loops main gained since the no-panics branch

Same treatment as the branch's `as_chunks` commit (Rust 1.99's
`chunks_exact_to_as_chunks` lint) for the flattener's coverage pass, the
CMYK ink compositor, the Flattener Preview highlight and four test helpers.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/engine/src/cmd/flatten.rs

@@ -938,7 +938,7 @@ fn render_raster(doc: &Document, art: &[Node], rect: Rect, ppi: f64, clip: Optio
             })
             .collect();
         let cover = r.render_region(&isolated_doc(doc, cover), region, scale, false);
-        for (px, c) in img.pixels.chunks_exact_mut(4).zip(cover.pixels.chunks_exact(4)) {
+        for (px, c) in img.pixels.as_chunks_mut::<4>().0.iter_mut().zip(cover.pixels.as_chunks::<4>().0) {
             let k = c[3];
             let k2 = if o.anti_alias || k == 0 || k == 255 {
                 k

crates/engine/src/tests_expand.rs

@@ -38,7 +38,13 @@ fn render(s: &Session) -> vectorcraft_render::Rendered {
 
 /// Pixels (of 200×200) whose colour differs by more than `tol` in any channel.
 fn differing(a: &vectorcraft_render::Rendered, b: &vectorcraft_render::Rendered, tol: u8) -> usize {
-    a.pixels.chunks_exact(4).zip(b.pixels.chunks_exact(4)).filter(|(p, q)| p.iter().zip(q.iter()).any(|(x, y)| x.abs_diff(*y) > tol)).count()
+    a.pixels
+        .as_chunks::<4>()
+        .0
+        .iter()
+        .zip(b.pixels.as_chunks::<4>().0)
+        .filter(|(p, q)| p.iter().zip(q.iter()).any(|(x, y)| x.abs_diff(*y) > tol))
+        .count()
 }
 
 fn expandable(s: &Session) -> bool {

crates/engine/src/tests_flatten.rs

@@ -108,7 +108,14 @@ fn assert_regions_match(s: &Session, before: &Rendered, group: u64, tol: u8, wha
 
 /// Share of pixels whose colour moved by more than 8/255.
 fn changed(a: &Rendered, b: &Rendered) -> f64 {
-    let n = a.pixels.chunks_exact(4).zip(b.pixels.chunks_exact(4)).filter(|(p, q)| p.iter().zip(q.iter()).any(|(x, y)| x.abs_diff(*y) > 8)).count();
+    let n = a
+        .pixels
+        .as_chunks::<4>()
+        .0
+        .iter()
+        .zip(b.pixels.as_chunks::<4>().0)
+        .filter(|(p, q)| p.iter().zip(q.iter()).any(|(x, y)| x.abs_diff(*y) > 8))
+        .count();
     n as f64 / (a.pixels.len() / 4) as f64
 }
 

crates/engine/src/tests_objexpand.rs

@@ -69,7 +69,13 @@ fn mean_diff(a: &vectorcraft_render::Rendered, b: &vectorcraft_render::Rendered)
 
 /// Pixels (of 200×200) whose colour differs by more than `tol` in any channel.
 fn differing(a: &vectorcraft_render::Rendered, b: &vectorcraft_render::Rendered, tol: u8) -> usize {
-    a.pixels.chunks_exact(4).zip(b.pixels.chunks_exact(4)).filter(|(p, q)| p.iter().zip(q.iter()).any(|(x, y)| x.abs_diff(*y) > tol)).count()
+    a.pixels
+        .as_chunks::<4>()
+        .0
+        .iter()
+        .zip(b.pixels.as_chunks::<4>().0)
+        .filter(|(p, q)| p.iter().zip(q.iter()).any(|(x, y)| x.abs_diff(*y) > tol))
+        .count()
 }
 
 fn white_black() -> Value {

crates/engine/src/tests_stylelib.rs

@@ -219,7 +219,7 @@ fn every_builtin_style_paints_visibly_on_a_rectangle() {
             run(&mut s, "graphicStyle.addFromLibrary", json!({"library": b.id, "name": g.name, "apply": true}));
             assert_eq!(doc(&s).node(id).unwrap().graphic_style, doc(&s).graphic_style(&g.name).map(|x| x.id), "{}", g.name);
             let img = renderer.render_region(doc(&s), Rect::new(0.0, 0.0, 100.0, 100.0), 0.5, true);
-            let painted = img.pixels.chunks_exact(4).filter(|p| p[..3] != [255, 255, 255]).count();
+            let painted = img.pixels.as_chunks::<4>().0.iter().filter(|p| p[..3] != [255, 255, 255]).count();
             assert!(painted > 40, "{} / {} paints {painted} pixels", b.id, g.name);
         }
     }

crates/render/src/ink.rs

@@ -204,7 +204,7 @@ pub(crate) fn compose(cmy: &[u8], k: &[u8], background: Option<[u8; 4]>) -> Vec<
     let mut out = Vec::with_capacity(cmy.len());
     // Runs of one colour convert once.
     let mut last: Option<([u8; 8], [u8; 4])> = None;
-    for (p, q) in cmy.chunks_exact(4).zip(k.chunks_exact(4)) {
+    for (p, q) in cmy.as_chunks::<4>().0.iter().zip(k.as_chunks::<4>().0) {
         let key = [p[0], p[1], p[2], p[3], q[0], q[1], q[2], q[3]];
         let px = match (&last, &bg) {
             _ if p[3] == 0 => [0; 4],

crates/ui-egui/src/panels/flattener_preview.rs

@@ -325,7 +325,7 @@ fn render(
             .highlight_art(&shot.doc, h)
             .map(|art| r.render(&art, w, hh, view, &RenderOptions { skip_templates: true, ..Default::default() }));
         let red = [color.r(), color.g(), color.b()].map(f32::from);
-        for (i, p) in img.pixels.chunks_exact_mut(4).enumerate() {
+        for (i, p) in img.pixels.as_chunks_mut::<4>().0.iter_mut().enumerate() {
             // A light grey of the art, so the highlight stands out.
             let luma = 0.299 * p[0] as f32 + 0.587 * p[1] as f32 + 0.114 * p[2] as f32;
             let grey = 96.0 + luma * 0.62;