M1: 2x pixel preview (#68)

Pixel preview takes a resolution: `view.pixelPreview {scale: 1|2}` turns it on at 1x (one rendered
pixel per page pixel) or 2x (two, as on a high-density display); the canvas renders at that
resolution from a whole-pixel origin and magnifies it with hard edges once zoomed past it. The zoom
menu offers "Pixel preview 1x" and "2x" and now shows the on/off state of every view toggle.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

ROADMAP.md

@@ -208,7 +208,7 @@ Scores by behaviour, 0–100%. Hours are what remains (one agent).
 
 | Area | Weight | Score | Remaining work | Hours |
 |---|---|---|---|---|
-| Canvas & navigation | 6 | 72% | frame guides, 2x pixel preview | 3–5 |
+| Canvas & navigation | 6 | 73% | frame guides | 2–4 |
 | Selection & transform | 8 | 68% | measure hover polish, scale tool on-canvas handles | 5–8 |
 | Layers panel | 5 | 79% | keyboard row navigation | 1–2 |
 | Shapes & vector | 8 | 74% | live boolean editing, arc handles on canvas, shape builder on strokes and open paths, one-sided widths | 4–8 |

crates/engine/src/cmd/view.rs

@@ -19,6 +19,23 @@ fn flag(s: &mut Session, p: &Value, f: fn(&mut ViewState) -> &mut bool) -> Resul
     Ok(json!({"on": *slot}))
 }
 
+/// Pixel preview: toggles, or turns on at a resolution of 1x or 2x.
+fn pixel_preview(s: &mut Session, p: &Value) -> Result<Value> {
+    let scale = match p.get("scale") {
+        None | Some(Value::Null) => None,
+        Some(v) => match v.as_u64() {
+            Some(k @ (1 | 2)) => Some(k as u8),
+            _ => return Err(bad("view.pixelPreview", "`scale` must be 1 or 2")),
+        },
+    };
+    let v = view(s)?;
+    if let Some(k) = scale {
+        v.pixel_scale = k;
+    }
+    v.pixel_preview = boolean(p, "on").unwrap_or(scale.is_some() || !v.pixel_preview);
+    Ok(json!({"on": v.pixel_preview, "scale": v.pixel_scale}))
+}
+
 fn zoom_to(s: &mut Session, z: f64) -> Result<Value> {
     let v = view(s)?;
     let c = (v.cx, v.cy);
@@ -140,7 +157,7 @@ pub fn specs() -> Vec<CommandSpec> {
         spec!("view.slices", "Slices", "{on?}", false, |s, p| flag(s, p, |v| &mut v.show_slices)),
         spec!("view.comments", "Comments", "{on?}", false, |s, p| flag(s, p, |v| &mut v.comments)),
         spec!("view.outlines", "Outlines", "{on?}", false, |s, p| flag(s, p, |v| &mut v.outlines)),
-        spec!("view.pixelPreview", "Pixel preview", "{on?}", false, |s, p| flag(s, p, |v| &mut v.pixel_preview)),
+        spec!("view.pixelPreview", "Pixel preview", "{on?, scale? (1|2: rendered pixels per page pixel; turns it on)}", false, pixel_preview),
         spec!("view.frameOutlines", "Frame outlines", "{on?}", false, |s, p| flag(s, p, |v| &mut v.frame_outlines)),
         spec!("view.snapGeometry", "Snap to geometry", "{on?}", false, |s, p| flag(s, p, |v| &mut v.snap_geometry)),
         spec!("view.snapObjects", "Snap to objects", "{on?}", false, |s, p| flag(s, p, |v| &mut v.snap_objects)),

crates/engine/src/lib.rs

@@ -104,6 +104,8 @@ pub struct ViewState {
     pub rulers: bool,
     pub outlines: bool,
     pub pixel_preview: bool,
+    /// Pixel preview resolution: rendered pixels per page pixel (1 or 2).
+    pub pixel_scale: u8,
     pub show_slices: bool,
     pub comments: bool,
     pub frame_outlines: bool,
@@ -126,6 +128,7 @@ impl Default for ViewState {
             rulers: false,
             outlines: false,
             pixel_preview: false,
+            pixel_scale: 1,
             show_slices: false,
             comments: true,
             frame_outlines: false,
@@ -894,6 +897,8 @@ mod nested_override_tests;
 #[cfg(test)]
 mod paint_tests;
 #[cfg(test)]
+mod pixel_preview_tests;
+#[cfg(test)]
 mod proto_multi_tests;
 #[cfg(test)]
 mod proto_present_tests;

crates/engine/src/pixel_preview_tests.rs

@@ -0,0 +1,38 @@
+//! Pixel preview: toggling it, and its 1x / 2x resolution.
+
+use serde_json::json;
+
+use crate::Session;
+
+fn preview(s: &Session) -> (bool, u8) {
+    let v = &s.ds().unwrap().view;
+    (v.pixel_preview, v.pixel_scale)
+}
+
+#[test]
+fn toggles_and_sets_its_resolution() {
+    let mut s = Session::new();
+    assert_eq!(preview(&s), (false, 1));
+    s.execute("view.pixelPreview", &json!({})).unwrap();
+    assert_eq!(preview(&s), (true, 1));
+    s.execute("view.pixelPreview", &json!({})).unwrap();
+    assert_eq!(preview(&s), (false, 1));
+    // A resolution turns it on.
+    let r = s.execute("view.pixelPreview", &json!({"scale": 2})).unwrap();
+    assert_eq!(r, json!({"on": true, "scale": 2}));
+    assert_eq!(preview(&s), (true, 2));
+    // Turning it off keeps the resolution for next time.
+    s.execute("view.pixelPreview", &json!({"on": false})).unwrap();
+    assert_eq!(preview(&s), (false, 2));
+    s.execute("view.pixelPreview", &json!({"on": true, "scale": 1})).unwrap();
+    assert_eq!(preview(&s), (true, 1));
+}
+
+#[test]
+fn rejects_other_resolutions() {
+    let mut s = Session::new();
+    for bad in [json!(3), json!(0), json!(1.5), json!("2"), json!(-1)] {
+        assert!(s.execute("view.pixelPreview", &json!({"scale": bad})).is_err(), "{bad}");
+    }
+    assert_eq!(preview(&s), (false, 1));
+}

crates/ui-egui/src/canvas.rs

@@ -140,7 +140,7 @@ pub fn show(app: &mut FigApp, ui: &mut Ui, worker: &mut Worker) {
         && done.generation == app.canvas.generation
     {
         // A pixel preview render is magnified with hard pixel edges.
-        let filter = if done.view.scale == 1.0 && app.session.ds().is_ok_and(pixel_preview) {
+        let filter = if app.session.ds().ok().and_then(pixel_preview) == Some(done.view.scale) {
             egui::TextureOptions::NEAREST
         } else {
             egui::TextureOptions::LINEAR
@@ -211,21 +211,22 @@ pub fn show(app: &mut FigApp, ui: &mut Ui, worker: &mut Worker) {
     }
 }
 
-/// Pixel preview is on and zoomed in past one screen pixel per page pixel.
-fn pixel_preview(ds: &figcraft_engine::DocState) -> bool {
-    ds.view.pixel_preview && ds.view.zoom > 1.0
+/// Pixel preview's resolution (rendered pixels per page pixel) when it's on and zoomed in past it.
+fn pixel_preview(ds: &figcraft_engine::DocState) -> Option<f64> {
+    let k = f64::from(ds.view.pixel_scale.clamp(1, 2));
+    (ds.view.pixel_preview && ds.view.zoom > k).then_some(k)
 }
 
 fn request_render(app: &mut FigApp, worker: &mut Worker, ppp: f32) {
     let Ok(ds) = app.session.ds() else { return };
     let rect = app.canvas.rect;
     let (mut ox, mut oy) = ds.view.origin();
-    let (scale, w, h) = if pixel_preview(ds) {
-        // Pixel preview: render one pixel per page unit from a whole-pixel origin, shown magnified
+    let (scale, w, h) = if let Some(k) = pixel_preview(ds) {
+        // Pixel preview: render `k` pixels per page unit from a whole-pixel origin, shown magnified
         // without smoothing.
-        (ox, oy) = (ox.floor(), oy.floor());
-        let z = ds.view.zoom.max(1e-9);
-        (1.0, (f64::from(rect.width()) / z).ceil() as u32 + 2, (f64::from(rect.height()) / z).ceil() as u32 + 2)
+        (ox, oy) = ((ox * k).floor() / k, (oy * k).floor() / k);
+        let z = ds.view.zoom.max(1e-9) / k;
+        (k, (f64::from(rect.width()) / z).ceil() as u32 + 2, (f64::from(rect.height()) / z).ceil() as u32 + 2)
     } else {
         (ds.view.zoom * f64::from(ppp), (rect.width() * ppp).ceil().max(1.0) as u32, (rect.height() * ppp).ceil().max(1.0) as u32)
     };

crates/ui-egui/src/right.rs

@@ -139,15 +139,23 @@ pub fn right_panel(app: &mut FigApp, ui: &mut Ui) {
             }
         }
         ui.separator();
-        for (label, cmd) in [
-            ("Pixel preview", "view.pixelPreview"),
-            ("Pixel grid", "view.pixelGrid"),
-            ("Snap to pixel grid", "view.snapPixel"),
-            ("Layout grids", "view.layoutGrids"),
-            ("Rulers", "view.rulers"),
-            ("Outlines", "view.outlines"),
-        ] {
-            if menu_item(ui, label, figcraft_engine::catalog::shortcut(cmd).unwrap_or("")) {
+        let Ok(v) = app.session.ds().map(|d| d.view.clone()) else { return };
+        for (label, scale) in [("Pixel preview 1x", 1u8), ("Pixel preview 2x", 2)] {
+            let on = v.pixel_preview && v.pixel_scale == scale;
+            if menu_check(ui, on, label, "") {
+                app.run("view.pixelPreview", json!({"on": !on, "scale": scale}));
+                ui.close();
+            }
+        }
+        let toggles: [(&str, &str, bool); 5] = [
+            ("Pixel grid", "view.pixelGrid", v.pixel_grid),
+            ("Snap to pixel grid", "view.snapPixel", v.snap_pixel),
+            ("Layout grids", "view.layoutGrids", v.layout_grids),
+            ("Rulers", "view.rulers", v.rulers),
+            ("Outlines", "view.outlines", v.outlines),
+        ];
+        for (label, cmd, on) in toggles {
+            if menu_check(ui, on, label, figcraft_engine::catalog::shortcut(cmd).unwrap_or("")) {
                 app.run(cmd, json!({}));
                 ui.close();
             }