Canvas: a document opens at the zoom of the settled window

A document without a saved view was fitted once, to the canvas of the first frame that shows it, and the window's layout can still move the canvas's edges over the next frames. Two starts of the app then opened one file at zooms a hair apart (4.9812 and 4.9883 in a CI probe of v0.21.0, the canvas and the view's centre alike).

The opening fit now follows the canvas until the view is moved or the user presses a button or a key, types, scrolls or zooms (CanvasCache::opening_fit). After that a canvas that changes keeps the view, as before.

crates/ui-egui/src/app.rs

@@ -89,6 +89,7 @@ impl VectorcraftApp {
                 view_moved: None,
                 hover_cursor: None,
                 presented: None,
+                opening_fit: None,
                 panes: Default::default(),
                 windows: crate::doc_windows::Windows::new(known),
             },

crates/ui-egui/src/caches.rs

@@ -65,6 +65,10 @@ pub struct CanvasCache {
     /// In Presentation Mode, the canvas rect the active artboard was last fitted to: it is fitted
     /// again when the rect changes (the window going full screen).
     pub presented: Option<egui::Rect>,
+    /// The canvas a document's opening view was fitted to, with the view the fit gave. The window's
+    /// layout can still move the canvas's edges over the next frames, so until the view is moved or
+    /// the user acts, the opening view is fitted again when the canvas changes ([`canvas::show`]).
+    pub opening_fit: Option<canvas::ViewKey>,
     /// Window › Arrange › Tile: the renders the panes of the other documents draw.
     pub panes: canvas::Panes,
     /// Window › Arrange › Float in Window: what the floating document windows keep between frames.

crates/ui-egui/src/canvas.rs

@@ -186,6 +186,22 @@ fn view_rects(app: &VectorcraftApp, outer: egui::Rect, ppp: f32) -> (egui::Rect,
     (full, rect.round_to_pixels(ppp))
 }
 
+/// Whether the user pressed a button or a key, typed, scrolled or zoomed in this frame: the
+/// opening fit stops following the canvas then ([`crate::caches::CanvasCache::opening_fit`]).
+fn acted(i: &egui::InputState) -> bool {
+    i.pointer.any_pressed()
+        || i.events.iter().any(|e| {
+            matches!(
+                e,
+                egui::Event::Key { pressed: true, .. }
+                    | egui::Event::Text(_)
+                    | egui::Event::MouseWheel { .. }
+                    | egui::Event::Zoom(_)
+                    | egui::Event::Touch { .. }
+            )
+        })
+}
+
 /// Paint the document canvas, complete or cached artwork, navigation and tool overlays.
 pub fn show(app: &mut VectorcraftApp, ui: &mut Ui) {
     let t = Tokens::get(ui.ctx());
@@ -225,13 +241,22 @@ pub fn show(app: &mut VectorcraftApp, ui: &mut Ui) {
     let (full, rect) = view_rects(app, outer, ui.ctx().pixels_per_point());
     app.canvas_rect = Some(rect);
     let fitted = app.view().is_some_and(|v| v.fitted);
+    // A document's opening view is fitted to the canvas of the first frame that shows it, and the
+    // window's layout can still move the canvas's edges over the next frames. Until the view is
+    // moved or the user acts, the opening fit follows the canvas, so that the document opens at the
+    // zoom of the settled window.
+    let key = |v: &View| ViewKey { rect, zoom: v.zoom, center: v.center, rotation: v.rotation };
+    let following =
+        !fitted || (!ui.input(acted) && app.canvas.opening_fit.zip(app.view()).is_some_and(|(was, v)| ViewKey { rect: was.rect, ..key(v) } == was));
+    let settling = fitted && following && app.canvas.opening_fit.is_some_and(|was| was.rect != rect);
     // Presentation Mode shows the active artboard on the whole screen and nothing but the art:
     // no selection, guides, grids or artboard edges (#4365).
     let presenting = app.ui.screen_mode == 3;
-    if !fitted || (presenting && app.canvas.presented != Some(rect)) {
+    if !fitted || settling || (presenting && app.canvas.presented != Some(rect)) {
         fit(app, "view.fitArtboard");
     }
     app.canvas.presented = presenting.then_some(rect);
+    app.canvas.opening_fit = if following { app.view().map(key) } else { None };
     // Before the canvas's own interaction, so the view the canvas draws is the one they moved to.
     if bars {
         scroll_bars(app, ui, rect, outer, &t);