Fix #755: blurred type no longer shifts as the view moves

Gaussian Blur and Feather drew through a filter layer whose blur works on
a coarser grid tied to the canvas: the blurred art moved by up to about
a pixel, and its steps showed, as the view moved by parts of a pixel
(scrolling, zooming about the pointer). They now blur the content's own
pixels on the CPU, as the Photoshop-style effects already do: the same
look wherever the view is, cached while only the view moves.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/render/src/fx.rs

@@ -187,10 +187,6 @@ fn shadow_filter(dx: f64, dy: f64, blur: f64, color: peniko::Color) -> Filter {
     })
 }
 
-fn blur_filter(sigma: f64) -> Filter {
-    Filter::from_primitive(FilterPrimitive::GaussianBlur { std_deviation: sigma.max(0.0) as f32, edge_mode: EdgeMode::None })
-}
-
 fn pcolor(ink: Ink, c: &vectorcraft_doc::color::Color) -> peniko::Color {
     let [r, g, b] = ink.rgb(c);
     peniko::Color::new([r, g, b, 1.0])
@@ -495,44 +491,12 @@ impl Renderer {
                 c.pop_layer();
             });
         }
-        // The content itself (blurred / feathered / filtered).
-        let blur: f64 = rfx
-            .iter()
-            .map(|fx| match fx {
-                RasterFx::Feather { radius } | RasterFx::GaussianBlur { radius } => radius.max(0.0),
-                _ => 0.0,
-            })
-            .sum();
-        if rfx.iter().any(|fx| matches!(fx, RasterFx::Pixel(_))) {
+        // The content itself (blurred / feathered / filtered), on its pixels: a filter layer's blur
+        // works on a coarser grid tied to the canvas, so the blurred art shifted by up to a pixel
+        // and looked blocky as the view moved by parts of a pixel (#755).
+        let blurs = rfx.iter().any(|fx| matches!(fx, RasterFx::Feather { radius } | RasterFx::GaussianBlur { radius } if *radius > 0.0));
+        if blurs || rfx.iter().any(|fx| matches!(fx, RasterFx::Pixel(_))) {
             self.pixel_content(ctx, f, content, rfx, paint);
-        } else if blur > 0.0 {
-            self.with_filters(ctx, f, reach, blur, None, |r, c, fr, _| {
-                let mut layers = 0;
-                for fx in rfx {
-                    match fx {
-                        RasterFx::Feather { radius } if *radius > 0.0 => {
-                            c.set_transform(fr.view);
-                            if let Some((g, rule)) = content.outline {
-                                c.set_fill_rule(fill_rule(rule));
-                                c.push_clip_layer(g);
-                                layers += 1;
-                            }
-                            c.push_layer(None, None, None, None, Some(blur_filter(radius / 2.0)));
-                            layers += 1;
-                        }
-                        RasterFx::GaussianBlur { radius } if *radius > 0.0 => {
-                            c.set_transform(fr.view);
-                            c.push_layer(None, None, None, None, Some(blur_filter(radius / 2.0)));
-                            layers += 1;
-                        }
-                        _ => {}
-                    }
-                }
-                paint(r, c, fr);
-                for _ in 0..layers {
-                    c.pop_layer();
-                }
-            });
         } else {
             paint(self, ctx, f);
         }

crates/render/src/lib.rs

@@ -1760,6 +1760,8 @@ mod tests_fontchange;
 #[cfg(test)]
 mod tests_freeform;
 #[cfg(test)]
+mod tests_fxzoom;
+#[cfg(test)]
 mod tests_isolation;
 #[cfg(test)]
 mod tests_knockout;

crates/render/src/tests_fxzoom.rs

@@ -0,0 +1,142 @@
+//! Raster effects stay where they are, and look the same, at every zoom and pan (#755).
+
+use serde_json::json;
+use vectorcraft_color::{BlendMode, Color, Paint};
+use vectorcraft_doc::text::{CharStyle, TextObject};
+use vectorcraft_doc::{Appearance, Effect, Node, NodeKind};
+use vectorcraft_geom::{Point, shapes};
+
+use super::*;
+
+/// Type blurred by `radius` points (Gaussian Blur, or Feather when `feather`) over a rectangle
+/// that overlays at half opacity; without the type when `radius` is `None`.
+fn scene(radius: Option<f64>, feather: bool) -> Document {
+    let mut d = Document::new(200.0, 100.0);
+    let l = d.layers[0].id;
+    let mut back = Node::path(
+        d.alloc_id(),
+        shapes::rectangle(Rect::new(0.0, 0.0, 200.0, 100.0)),
+        Appearance::basic(Paint::solid(Color::rgb(0.2, 0.4, 0.9)), Paint::None, 0.0),
+    );
+    back.blend = BlendMode::Overlay;
+    back.opacity = 0.5;
+    d.insert(Some(l), 0, back).unwrap();
+    if let Some(radius) = radius {
+        let style = CharStyle { size: 36.0, ..CharStyle::default() };
+        let mut t = Node::new(d.alloc_id(), NodeKind::Text(Box::new(TextObject::point(Point::new(30.0, 60.0), "Hello", style))));
+        let id = if feather { "stylize.feather" } else { "blur.gaussian" };
+        t.appearance.effects.push(Effect { id: id.into(), params: json!({"radius": radius}), visible: true });
+        d.insert(Some(l), 1, t).unwrap();
+    }
+    d
+}
+
+/// `d` with its layer's art in one group: the overlay and the type grouped, as in #755's report.
+fn grouped(mut d: Document) -> Document {
+    let l = d.layers[0].id;
+    let id = d.alloc_id();
+    let members = d.children_mut(Some(l)).map(std::mem::take).unwrap();
+    d.insert(Some(l), 0, Node::new(id, NodeKind::Group { children: members, clip: false })).unwrap();
+    d
+}
+
+/// The canvas's options: art on nothing, no artboards.
+fn screen() -> RenderOptions {
+    RenderOptions { background: None, artboards: false, ..Default::default() }
+}
+
+fn render(d: &Document, threads: u16, view: Affine, (w, h): (u32, u32)) -> Rendered {
+    let mut r = Renderer::new();
+    r.threads = threads;
+    r.render(d, w, h, view, &screen())
+}
+
+/// Where the type's ink is on the document (its centroid), rendered `threads`-threaded through
+/// `view` on a `w` × `h` canvas.
+fn ink_centre(radius: f64, threads: u16, view: Affine, size: (u32, u32)) -> Point {
+    let with = render(&scene(Some(radius), false), threads, view, size);
+    let without = render(&scene(None, false), threads, view, size);
+    let (mut sx, mut sy, mut sw) = (0.0, 0.0, 0.0);
+    for (i, (p, q)) in with.pixels.chunks(4).zip(without.pixels.chunks(4)).enumerate() {
+        let d: f64 = (0..4).map(|c| f64::from(p[c].abs_diff(q[c]))).sum();
+        let (x, y) = ((i % size.0 as usize) as f64 + 0.5, (i / size.0 as usize) as f64 + 0.5);
+        sx += d * x;
+        sy += d * y;
+        sw += d;
+    }
+    assert!(sw > 0.0, "the type shows");
+    view.inverse() * Point::new(sx / sw, sy / sw)
+}
+
+#[test]
+fn blurred_type_stays_in_place_at_every_zoom_and_pan() {
+    for (radius, threads) in [(3.0, 0), (3.0, 4), (12.0, 0), (12.0, 4)] {
+        let base = ink_centre(radius, threads, Affine::IDENTITY, (200, 100));
+        // The whole document in view, at other zooms and moved by parts of a pixel.
+        for (zoom, pan) in
+            [(1.0, (13.3, 7.6)), (2.0, (41.7, 20.2)), (3.3, (15.25, 9.5)), (0.5, (10.4, 5.1)), (6.0, (30.6, 25.3)), (1.37, (0.5, 0.25))]
+        {
+            let view = Affine::translate(pan) * Affine::scale(zoom);
+            let size = ((200.0 * zoom + 2.0 * pan.0).ceil() as u32, (100.0 * zoom + 2.0 * pan.1).ceil() as u32);
+            let at = ink_centre(radius, threads, view, size);
+            assert!(
+                (at.x - base.x).abs() < 1.0 && (at.y - base.y).abs() < 1.0,
+                "radius {radius}, threads {threads}, zoom {zoom}, pan {pan:?}: {at:?} vs {base:?}"
+            );
+        }
+    }
+}
+
+/// Scrolling moves the blurred type with the page and nothing else: two views a whole number of
+/// pixels apart draw the same pixels where they overlap, whether the type fits on the canvas or
+/// runs off it.
+#[test]
+fn scrolling_moves_blurred_type_without_changing_it() {
+    for (feather, group) in [(false, false), (true, false), (false, true)] {
+        let d = scene(Some(12.0), feather);
+        let d = if group { grouped(d) } else { d };
+        for threads in [0, 4] {
+            for (zoom, (w, h)) in [(1.0, (240, 140)), (4.0, (500, 300)), (8.0, (400, 300))] {
+                let at = |dx: f64, dy: f64| render(&d, threads, Affine::translate((-dx, -dy)) * Affine::scale(zoom), (w, h));
+                let a = at(20.0, 10.0);
+                for (sx, sy) in [(1u32, 0u32), (3, 2), (37, 23), (101, 57)] {
+                    let b = at(20.0 + f64::from(sx), 10.0 + f64::from(sy));
+                    let mut worst = 0;
+                    for y in sy..h {
+                        for x in sx..w {
+                            let i = ((y * w + x) * 4) as usize;
+                            let j = (((y - sy) * w + x - sx) * 4) as usize;
+                            for c in 0..4 {
+                                worst = worst.max(a.pixels[i + c].abs_diff(b.pixels[j + c]));
+                            }
+                        }
+                    }
+                    assert!(
+                        worst <= 3,
+                        "feather {feather}, grouped {group}, threads {threads}, zoom {zoom}, scrolled by ({sx}, {sy}): a pixel changed by {worst}"
+                    );
+                }
+            }
+        }
+    }
+}
+
+/// Scrolling by parts of a pixel (a trackpad, a zoom about the pointer) moves heavily blurred type
+/// by just that: its ink stays put on the page within a tenth of a pixel, at any zoom.
+#[test]
+fn blurred_type_doesnt_wobble_as_the_view_moves_by_parts_of_a_pixel() {
+    for threads in [0, 4] {
+        for zoom in [1.0, 4.0] {
+            let at = |p: f64| {
+                ink_centre(30.0, threads, Affine::translate((400.0 - 75.0 * zoom + p, 330.0 - 48.0 * zoom + p)) * Affine::scale(zoom), (800, 660))
+            };
+            let base = at(0.0);
+            for k in 1..10 {
+                let c = at(f64::from(k) * 0.1);
+                // How far it moved on the screen, besides the view's own move.
+                let (dx, dy) = ((c.x - base.x) * zoom, (c.y - base.y) * zoom);
+                assert!(dx.abs() < 0.1 && dy.abs() < 0.1, "threads {threads}, zoom {zoom}, moved by {}: off by ({dx}, {dy}) px", f64::from(k) * 0.1);
+            }
+        }
+    }
+}

crates/ui-egui/src/control.rs

@@ -335,10 +335,9 @@ pub fn handle(app: &mut VectorcraftApp, ctx: &egui::Context, req: &ControlReques
             // No save dialog for an agent: the bytes come back, as in headless mode.
             None => wrap(app.run("document.export", p.clone())),
         },
-        "app.quit" => {
-            ctx.send_viewport_cmd(egui::ViewportCommand::Close);
-            ok(Value::Null)
-        }
+        // As the menu's Quit: `{"pending": "saveChanges"}` while a modified document is asked
+        // about; otherwise null, and the host closes the window (#830).
+        "app.quit" => wrap(app.run("app.quit", json!({}))),
         other => err(format!("unknown method `{other}`")),
     }
 }

crates/ui-egui/src/unsaved.rs

@@ -206,4 +206,23 @@ mod tests {
         app.run("app.quit", json!({})).unwrap();
         assert_eq!(app.ui.status, "quit");
     }
+
+    #[test]
+    fn the_control_channels_quit_says_when_it_asks_first() {
+        // #830: it answered null at once, before the question.
+        let (mut app, _) = app();
+        let ctx = egui::Context::default();
+        let quit = |app: &mut VectorcraftApp| {
+            let (req, _rx) = crate::control::ControlRequest::new("app.quit", json!({}));
+            let crate::control::Outcome::Done(r) = crate::control::handle(app, &ctx, &req) else { panic!("not done") };
+            r
+        };
+        new_doc(&mut app, true);
+        assert_eq!(quit(&mut app), json!({"ok": true, "result": {"pending": KIND}}));
+        assert_eq!((pending(&app), app.ui.status.as_str()), (Some(0), ""));
+        app.ui.dialog = None;
+        app.run("file.save", json!({"path": "/docs/saved.vectorcraft"})).unwrap();
+        assert_eq!(quit(&mut app), json!({"ok": true, "result": null}));
+        assert_eq!(app.ui.status, "quit");
+    }
 }