Fix #82: the window fits the screen and comes back where it was

The first window opens at 1440 x 900 when the screen has room for it around a
taskbar or Dock, and maximized (with a size that fits once un-maximized)
when it doesn't, as on 1600 x 900, 1366 x 768 or 150% scaled 1080p screens.
The window's size, position and maximized state are saved with the UI
preferences (UiState::window) and restored at the next launch, moved fully
onto a monitor that is still connected and maximized if it no longer fits.

Root cause: main.rs created the window at a fixed 1440 x 900 at the system's
default position, never checked it against the monitor and never remembered
it. The new apps/vectorcraft/src/window.rs places the still-hidden window
from the monitors winit reports (CreationContext::winit_window) and tracks
its geometry every frame.

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

Cargo.lock

@@ -4225,6 +4225,7 @@ dependencies = [
  "vectorcraft-engine",
  "vectorcraft-ui-egui",
  "webbrowser",
+ "winit",
  "winresource",
 ]
 

apps/vectorcraft/Cargo.toml

@@ -22,6 +22,8 @@ rfd = { workspace = true }
 arboard = { workspace = true, features = ["image-data"] }
 image = { workspace = true }
 webbrowser = { workspace = true }
+# The window's monitors, size and position (the same winit eframe runs on).
+winit = { version = "0.30", default-features = false }
 
 [target.'cfg(windows)'.dependencies]
 clipboard-win = { workspace = true }

apps/vectorcraft/src/main.rs

@@ -11,6 +11,7 @@ mod control_server;
 #[cfg(target_os = "macos")]
 mod native_menu;
 mod printing;
+mod window;
 
 use vectorcraft_engine::Session;
 use vectorcraft_engine::cmd::fileio;
@@ -30,6 +31,7 @@ impl eframe::App for App {
             }
         }
         self.0.logic(ctx);
+        window::track(ctx, &mut self.0.ui.window);
         if self.0.ui.status == "quit" {
             ctx.send_viewport_cmd(egui::ViewportCommand::Close);
         }
@@ -71,21 +73,32 @@ fn prefs_path_for(name: &str, lower: &str) -> Option<std::path::PathBuf> {
     base.map(|b| b.join("ui.json"))
 }
 
-fn load_prefs(app: &mut VectorcraftApp) {
+/// Runs without preferences (`VECTORCRAFT_NO_PREFS`, agents' test runs) neither read nor write them.
-    if std::env::var_os("VECTORCRAFT_NO_PREFS").is_some() {
+fn prefs_enabled() -> bool {
+    std::env::var_os("VECTORCRAFT_NO_PREFS").is_none()
+}
+
+/// The saved UI preferences, read before the window opens (they hold its size and position).
+fn read_prefs() -> Option<vectorcraft_ui_egui::UiState> {
+    if !prefs_enabled() {
+        return None;
+    }
+    let bytes = prefs_path().and_then(|p| std::fs::read(p).ok()).or_else(|| legacy_prefs_path().and_then(|p| std::fs::read(p).ok()))?;
+    serde_json::from_slice(&bytes).ok()
+}
+
+fn load_prefs(app: &mut VectorcraftApp, saved: Option<vectorcraft_ui_egui::UiState>) {
+    if !prefs_enabled() {
         return;
     }
-    let bytes = prefs_path().and_then(|p| std::fs::read(p).ok()).or_else(|| legacy_prefs_path().and_then(|p| std::fs::read(p).ok()));
+    if let Some(ui) = saved {
-    if let Some(bytes) = bytes
-        && let Ok(ui) = serde_json::from_slice::<vectorcraft_ui_egui::UiState>(&bytes)
-    {
         app.ui = ui.sanitized();
     }
     vectorcraft_ui_egui::prefs_dialog::restore(app);
 }
 
 fn save_prefs(app: &VectorcraftApp) {
-    if std::env::var_os("VECTORCRAFT_NO_PREFS").is_some() {
+    if !prefs_enabled() {
         return;
     }
     if let Some(p) = prefs_path() {
@@ -230,11 +243,13 @@ fn main() -> eframe::Result {
             _ => files.push(a),
         }
     }
+    let saved = read_prefs();
+    let saved_window = saved.as_ref().and_then(|ui| ui.window);
     let options = eframe::NativeOptions {
         viewport: egui::ViewportBuilder::default()
             .with_title("VectorCraft")
-            .with_inner_size([1440.0, 900.0])
+            .with_inner_size(window::DEFAULT_SIZE)
-            .with_min_inner_size([800.0, 500.0])
+            .with_min_inner_size(window::MIN_SIZE)
             .with_drag_and_drop(true)
             .with_decorations(!CUSTOM_TITLEBAR)
             .with_fullsize_content_view(true)
@@ -249,7 +264,11 @@ fn main() -> eframe::Result {
         options,
         Box::new(move |cc| {
             let mut app = VectorcraftApp::new(Session::new(), services());
-            load_prefs(&mut app);
+            load_prefs(&mut app, saved);
+            // Fit the window to its monitor, or put it back where it was (still hidden).
+            if let Some(w) = cc.winit_window() {
+                app.ui.window = Some(window::restore(w, saved_window));
+            }
             // User Defined swatch and graphic style libraries live next to the preferences.
             let swatches = prefs_path().and_then(|p| Some(p.parent()?.join("Swatches").to_string_lossy().to_string()));
             app.session.swatch_libraries.set_user_dir(swatches);

apps/vectorcraft/src/window.rs

@@ -0,0 +1,256 @@
+//! The main window's size and position. The first launch fits the window to its monitor, opening
+//! it maximized where the default size leaves no room for a taskbar or Dock. Later launches restore
+//! the size, position and maximized state saved with the UI preferences (`UiState::window`), moved
+//! onto a monitor that is still connected.
+
+use vectorcraft_ui_egui::state::WindowGeometry;
+use winit::dpi::{LogicalSize, PhysicalPosition, PhysicalSize};
+
+/// The first window's size, in points.
+pub const DEFAULT_SIZE: [f32; 2] = [1440.0, 900.0];
+/// The smallest window, in points.
+pub const MIN_SIZE: [f32; 2] = [800.0, 500.0];
+/// Room the first window leaves around itself for a taskbar, Dock or menu bar (the system doesn't
+/// say how much of the screen they take): a monitor with less room opens it maximized.
+const SCREEN_ROOM: [f32; 2] = [64.0, 128.0];
+
+/// A monitor: its top-left corner and size in physical pixels, and its scale factor.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Monitor {
+    pos: [i64; 2],
+    size: [i64; 2],
+    scale: f32,
+}
+
+impl Monitor {
+    pub fn new(pos: PhysicalPosition<i32>, size: PhysicalSize<u32>, scale: f64) -> Self {
+        let scale = scale as f32;
+        let scale = if scale.is_finite() && scale > 0.0 { scale } else { 1.0 };
+        Self { pos: [pos.x.into(), pos.y.into()], size: [size.width.into(), size.height.into()], scale }
+    }
+
+    /// Its size in points.
+    fn points(&self) -> [f32; 2] {
+        self.size.map(|s| s as f32 / self.scale)
+    }
+
+    /// Its size in points less room for a taskbar, Dock or menu bar.
+    fn usable(&self) -> [f32; 2] {
+        let points = self.points();
+        std::array::from_fn(|i| points[i] - SCREEN_ROOM[i])
+    }
+
+    /// A window of `size` points on this monitor, in physical pixels.
+    fn pixels(&self, size: [f32; 2]) -> [i64; 2] {
+        size.map(|s| (s * self.scale) as i64)
+    }
+
+    /// How much of a window at `pos` of `size` points this monitor shows, in square pixels.
+    fn overlap(&self, pos: [i32; 2], size: [f32; 2]) -> i64 {
+        let px = self.pixels(size);
+        let span = |i: usize| {
+            let start = i64::from(pos[i]).max(self.pos[i]);
+            let end = i64::from(pos[i]).saturating_add(px[i]).min(self.pos[i] + self.size[i]);
+            (end - start).max(0)
+        };
+        span(0).saturating_mul(span(1))
+    }
+
+    /// The top-left corner nearest to `pos` (centred when none) that keeps a window of `size`
+    /// points on this monitor.
+    fn keep_on(&self, pos: Option<[i32; 2]>, size: [f32; 2]) -> [i32; 2] {
+        let px = self.pixels(size);
+        std::array::from_fn(|i| {
+            let lo = self.pos[i];
+            let hi = lo + self.size[i].saturating_sub(px[i]).max(0);
+            let want = pos.map_or(lo + (hi - lo) / 2, |p| i64::from(p[i]));
+            i32::try_from(want.max(lo).min(hi)).unwrap_or_default()
+        })
+    }
+}
+
+/// Where the window opens: `saved` (the last session's geometry) kept on a connected monitor, else
+/// the default size on `home` (the monitor the system opens it on). Without monitors (the system
+/// doesn't list them, so nothing to check a saved geometry against) the default size.
+pub fn place(saved: Option<WindowGeometry>, monitors: &[Monitor], home: Option<usize>) -> WindowGeometry {
+    let default = WindowGeometry { pos: None, size: DEFAULT_SIZE, maximized: false };
+    let Some(home) = home.and_then(|i| monitors.get(i)).or(monitors.first()) else {
+        return default;
+    };
+    let Some(saved) = saved else {
+        let usable = home.usable();
+        if (0..2).all(|i| DEFAULT_SIZE[i] <= usable[i]) {
+            return default;
+        }
+        // A small screen: maximized, with a size that fits once un-maximized.
+        let size = fit(DEFAULT_SIZE, usable);
+        return WindowGeometry { pos: Some(home.keep_on(None, size)), size, maximized: true };
+    };
+    // The monitor showing most of the window; none when it was on a monitor that is gone.
+    let shown = saved.pos.and_then(|p| {
+        let (area, m) = monitors.iter().map(|m| (m.overlap(p, saved.size), m)).max_by_key(|(area, _)| *area)?;
+        (area > 0).then_some(m)
+    });
+    let m = shown.unwrap_or(home);
+    // Bigger than its monitor (a smaller screen than last time): maximized, like the first window.
+    let room = m.points();
+    let too_big = (0..2).any(|i| saved.size[i] > room[i]);
+    let size = fit(saved.size, if too_big { m.usable() } else { room });
+    WindowGeometry {
+        // Moved fully onto its monitor, or centred on the home monitor.
+        pos: saved.pos.map(|p| m.keep_on(shown.map(|_| p), size)),
+        size,
+        maximized: saved.maximized || too_big,
+    }
+}
+
+/// `size` no bigger than `room`, and no smaller than the smallest window unless `room` is.
+fn fit(size: [f32; 2], room: [f32; 2]) -> [f32; 2] {
+    std::array::from_fn(|i| size[i].min(room[i]).max(MIN_SIZE[i].min(room[i])).max(1.0))
+}
+
+/// Size and place the new window (eframe shows it after drawing the first frame) and return its
+/// geometry.
+pub fn restore(window: &winit::window::Window, saved: Option<WindowGeometry>) -> WindowGeometry {
+    let handles: Vec<_> = window.available_monitors().collect();
+    let monitors: Vec<Monitor> = handles.iter().map(|m| Monitor::new(m.position(), m.size(), m.scale_factor())).collect();
+    let home = window.current_monitor().or_else(|| window.primary_monitor()).and_then(|c| handles.iter().position(|m| *m == c));
+    let g = place(saved, &monitors, home);
+    if let Some([x, y]) = g.pos {
+        window.set_outer_position(PhysicalPosition::new(x, y));
+    }
+    // Returns the new size when it applies at once; either way the window gets it.
+    let _ = window.request_inner_size(LogicalSize::new(g.size[0], g.size[1]));
+    if g.maximized {
+        window.set_maximized(true);
+    }
+    g
+}
+
+/// Per frame: remember the window's geometry for the next launch. Minimized or full screen keeps
+/// the last one; maximized only sets its flag, so un-maximizing next time restores the last size.
+pub fn track(ctx: &egui::Context, geometry: &mut Option<WindowGeometry>) {
+    let zoom = ctx.zoom_factor();
+    ctx.input(|i| {
+        let v = i.viewport();
+        if v.minimized == Some(true) || v.fullscreen == Some(true) {
+            return;
+        }
+        if v.maximized == Some(true) {
+            if let Some(g) = geometry {
+                g.maximized = true;
+            }
+            return;
+        }
+        let Some(inner) = v.inner_rect else { return };
+        let pos = v.outer_rect.map(|r| [r.min.x, r.min.y].map(|c| (c * i.pixels_per_point).round() as i32));
+        *geometry = Some(WindowGeometry { pos, size: [inner.width() * zoom, inner.height() * zoom], maximized: false });
+    });
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn monitor(x: i32, y: i32, w: u32, h: u32, scale: f64) -> Monitor {
+        Monitor::new(PhysicalPosition::new(x, y), PhysicalSize::new(w, h), scale)
+    }
+
+    fn saved(pos: Option<[i32; 2]>, size: [f32; 2], maximized: bool) -> Option<WindowGeometry> {
+        Some(WindowGeometry { pos, size, maximized })
+    }
+
+    #[test]
+    fn the_first_window_fits_its_screen() {
+        // 1920 × 1080: the default size, where the system puts it.
+        let big = [monitor(0, 0, 1920, 1080, 1.0)];
+        assert_eq!(place(None, &big, Some(0)), WindowGeometry { pos: None, size: DEFAULT_SIZE, maximized: false });
+        // 1600 × 900, 1366 × 768 and 1920 × 1080 at 150% (1280 × 720 points): maximized, and a
+        // size that fits the screen with room for the taskbar once un-maximized.
+        for (m, size) in [
+            (monitor(0, 0, 1600, 900, 1.0), [1440.0, 772.0]),
+            (monitor(0, 0, 1366, 768, 1.0), [1302.0, 640.0]),
+            (monitor(0, 0, 1920, 1080, 1.5), [1216.0, 592.0]),
+        ] {
+            let g = place(None, &[m], Some(0));
+            assert!(g.maximized, "{m:?}");
+            assert_eq!(g.size, size, "{m:?}");
+            let [x, y] = g.pos.unwrap();
+            let px = m.pixels(g.size);
+            assert!(x >= 0 && y >= 0 && i64::from(x) + px[0] <= m.size[0] && i64::from(y) + px[1] <= m.size[1], "{m:?}: {g:?}");
+        }
+        // No monitor information: the default size, whatever was saved.
+        assert_eq!(place(None, &[], None), WindowGeometry { pos: None, size: DEFAULT_SIZE, maximized: false });
+        assert_eq!(place(saved(Some([9000, 9000]), [1e9, 1e9], true), &[], None).size, DEFAULT_SIZE);
+    }
+
+    #[test]
+    fn the_saved_window_comes_back_where_it_was() {
+        let two = [monitor(0, 0, 2560, 1440, 1.0), monitor(2560, 0, 1920, 1080, 1.0)];
+        for g in [saved(Some([100, 80]), [1200.0, 800.0], false), saved(Some([2700, 50]), [1000.0, 700.0], true), saved(None, [1000.0, 700.0], false)]
+        {
+            assert_eq!(Some(place(g, &two, Some(0))), g);
+        }
+    }
+
+    #[test]
+    fn a_saved_window_stays_on_a_connected_monitor() {
+        let laptop = [monitor(0, 0, 1600, 900, 1.0)];
+        // Last time on a second monitor that is gone: centred on the remaining one.
+        let g = place(saved(Some([2700, 50]), [1000.0, 700.0], false), &laptop, Some(0));
+        assert_eq!(g, WindowGeometry { pos: Some([300, 100]), size: [1000.0, 700.0], maximized: false });
+        // Half off the monitor's right and bottom edges: moved fully onto it.
+        let g = place(saved(Some([1200, 600]), [1000.0, 700.0], false), &laptop, Some(0));
+        assert_eq!(g.pos, Some([600, 200]));
+        // Bigger than the screen now (it was on a larger one): it fits, and opens maximized.
+        let g = place(saved(Some([0, 0]), [2400.0, 1300.0], false), &laptop, Some(0));
+        assert_eq!(g, WindowGeometry { pos: Some([0, 0]), size: [1536.0, 772.0], maximized: true });
+        // A monitor left of the primary one (negative coordinates) still counts.
+        let left = [monitor(0, 0, 1920, 1080, 1.0), monitor(-1920, 0, 1920, 1080, 1.0)];
+        assert_eq!(place(saved(Some([-1800, 40]), [1000.0, 700.0], false), &left, Some(0)).pos, Some([-1800, 40]));
+        // Nonsense sizes from a damaged preferences file are kept within the screen.
+        let g = place(saved(Some([i32::MAX, i32::MIN]), [-5.0, f32::MAX], false), &laptop, Some(0));
+        assert_eq!(g, WindowGeometry { pos: Some([400, 64]), size: [800.0, 772.0], maximized: true });
+        let g = place(saved(Some([5, 5]), [f32::NEG_INFINITY, f32::INFINITY], false), &laptop, Some(0));
+        assert_eq!(g, WindowGeometry { pos: Some([400, 64]), size: [800.0, 772.0], maximized: true });
+    }
+
+    #[test]
+    fn the_window_geometry_is_tracked_for_the_next_launch() {
+        let ctx = egui::Context::default();
+        let mut geometry = None;
+        let mut frame = |info: egui::ViewportInfo| {
+            let mut input = egui::RawInput::default();
+            input.viewports.insert(egui::ViewportId::ROOT, info);
+            ctx.run_ui(input, |ui| track(ui.ctx(), &mut geometry)).textures_delta.clear();
+            geometry
+        };
+        let rect = egui::Rect::from_min_size(egui::pos2(20.0, 30.0), egui::vec2(1000.0, 600.0));
+        let normal = egui::ViewportInfo {
+            native_pixels_per_point: Some(1.5),
+            inner_rect: Some(rect),
+            outer_rect: Some(rect),
+            maximized: Some(false),
+            ..Default::default()
+        };
+        // Position in physical pixels, size in points.
+        let g = WindowGeometry { pos: Some([30, 45]), size: [1000.0, 600.0], maximized: false };
+        assert_eq!(frame(normal.clone()), Some(g));
+        // Maximized or minimized: the size to restore stays.
+        let big = egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(1280.0, 700.0));
+        let maximized = egui::ViewportInfo { inner_rect: Some(big), outer_rect: Some(big), maximized: Some(true), ..normal.clone() };
+        assert_eq!(frame(maximized), Some(WindowGeometry { maximized: true, ..g }));
+        let minimized = egui::ViewportInfo { inner_rect: None, outer_rect: None, minimized: Some(true), ..normal.clone() };
+        assert_eq!(frame(minimized), Some(WindowGeometry { maximized: true, ..g }));
+        assert_eq!(frame(normal), Some(g));
+        // Saved with the preferences; older preference files have no window.
+        let mut ui = vectorcraft_ui_egui::UiState { window: Some(g), ..Default::default() };
+        let back: vectorcraft_ui_egui::UiState = serde_json::from_slice(&serde_json::to_vec(&ui).unwrap()).unwrap();
+        assert_eq!(back.window, Some(g));
+        ui.window = None;
+        let json = serde_json::to_value(&ui).unwrap();
+        assert!(json.get("window").is_none());
+        let back: vectorcraft_ui_egui::UiState = serde_json::from_value(json).unwrap();
+        assert_eq!(back.window, None);
+    }
+}

crates/ui-egui/src/state.rs

@@ -303,6 +303,24 @@ pub struct UiState {
     /// becoming active, leaves it.
     #[serde(skip)]
     pub home: Option<(Option<u64>, usize)>,
+    /// The desktop window's size, position and maximized state, saved when the app quits and
+    /// restored at the next launch (the desktop host reads and writes it; none on the web).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub window: Option<WindowGeometry>,
+}
+
+/// The desktop window's geometry, kept across launches.
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
+pub struct WindowGeometry {
+    /// Top-left corner of the window frame, in physical pixels on the desktop (none where the
+    /// system doesn't tell windows where they are).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub pos: Option<[i32; 2]>,
+    /// Size of the window's contents in logical pixels (points at 100% UI scaling).
+    pub size: [f32; 2],
+    /// The window was maximized; `pos` and `size` are where un-maximizing puts it.
+    #[serde(default)]
+    pub maximized: bool,
 }
 
 impl UiState {
@@ -365,6 +383,7 @@ impl Default for UiState {
             eps_options: Value::Null,
             dxf_import: Value::Null,
             home: None,
+            window: None,
         }
     }
 }