Let the page fling work anywhere, with a setting to turn it off

A fling toward a free side of the active page now offers a page at any
zoom or pan position, not only once that edge is on screen. If the
side's plus is visible it pulses as before; otherwise an "Add page"
button appears at that edge of the screen, tapped through the same
palm-checked gesture as the plus.

Settings → Pen & touch gets "Swipe to add pages" (on by default).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GaoZtJQZwLXkEgWs8twCia

README.md

@@ -23,7 +23,7 @@ The image builds the PWA and serves it with nginx. Put an HTTPS reverse proxy in
 ## Using it
 
 - **Tools** (bottom bar): Text `T`, Pen `P`, Highlighter `H`, Eraser `E`, Import PDF, Undo/Redo, zoom. The pen's eraser end erases too.
-- **Pages**: the "+" circles beside the active page add a page there (a quick finger fling past a free edge highlights that side's "+"); `Alt+Arrow` moves to (or creates) the neighbour. Right-click a page or use its `⋯` button to insert, resize or delete it.
+- **Pages**: the "+" circles beside the active page add a page there (a quick finger flick toward a free side offers one there; turn it off under Settings → Pen & touch); `Alt+Arrow` moves to (or creates) the neighbour. Right-click a page or use its `⋯` button to insert, resize or delete it.
 - **Grid**: the faint background grid has one cell per active page; Settings → Appearance can hide it or subdivide it.
 - **Importing a PDF** into a non-empty canvas shows every free spot; click one to place the chain. Into a blank canvas it simply replaces the empty page. The Files panel can also import a PDF as a new canvas.
 - **View**: wheel/trackpad pans, `Ctrl`+wheel or pinch zooms, `Ctrl+0` fits the page, `Ctrl+9` shows the whole tree, space-drag or middle-drag pans.

spec.md

@@ -9,7 +9,7 @@ One canvas = one tree = one `.pdf` file.
   - A branch can only ever continue in the direction it started (strictly linear — no sub-branches off a branch).
   - A trunk page can have at most one left branch and one right branch.
 - **PDF import**: creates a chain of pages in whatever direction you pick when placing it (up/down = extends the trunk, left/right = becomes a branch off the trunk page you clicked). Only one trunk exists per canvas — additional imported PDFs must attach as a branch off some trunk page, or extend an existing branch further outward in its established direction.
-- Each free side of the active page shows a small "+" circle just off its edge; tapping it (or `Alt+Arrow`) adds a blank page there. A quick finger fling past a free edge highlights that side's "+" for a few seconds, but never adds a page by itself.
+- Each free side of the active page shows a small "+" circle just off its edge; tapping it (or `Alt+Arrow`) adds a blank page there. A quick finger fling toward a free side offers a page there for a few seconds: that side's "+" pulses, or, if it is off screen, an "Add page" button appears at that edge of the screen. The fling never adds a page by itself, and can be turned off in Settings.
 - The canvas background is a faint grid with one cell per active page, aligned to its edges; Settings can hide it or subdivide it.
 - Deleting a page removes it (undo via Ctrl+Z); no permanent trash.
 - Default zoom: one page fills the screen. Zoom out reveals the tree.

src/lib/components/CanvasView.svelte

@@ -119,7 +119,8 @@
 
 	const placeSlots = $derived(tools.placing ? freeSlots(doc.tree) : []);
 
-	// A finger fling past the active page's free edge highlights the plus on that side.
+	// A finger fling toward a free side of the active page offers a new page there: the plus
+	// pulses if it's on screen, otherwise a button appears at that edge of the screen.
 	let offer = $state<Slot | null>(null);
 	let offerTimer: ReturnType<typeof setTimeout> | undefined;
 
@@ -130,18 +131,21 @@
 	}
 
 	function offerAfterFling(samples: Sample[]) {
+		if (!settings.data.flingToAdd) return;
 		const dir = flingDir(samples);
 		const id = doc.activeId;
-		const r = id && doc.rects.get(id);
 		const slot = dir && ghostSlots.find((s) => s.anchor === id && s.dir === dir);
-		if (!r || !slot) return;
-		// Only once that edge has come into view, i.e. the fling went past the end.
+		if (slot) setOffer(slot);
+	}
+
+	/** The offered plus is off screen, so the offer shows as an edge-of-screen button instead. */
+	const offerOffscreen = $derived.by(() => {
+		const r = offer && plusRect(offer);
+		if (!r) return false;
 		const a = viewport.toScreen(r.x, r.y);
 		const b = viewport.toScreen(r.x + r.width, r.y + r.height);
-		const edge = { left: a.x, right: b.x, up: a.y, down: b.y }[slot.dir];
-		const size = slot.dir === 'left' || slot.dir === 'right' ? viewport.width : viewport.height;
-		if (edge >= 0 && edge <= size) setOffer(slot);
-	}
+		return b.x < 0 || b.y < 0 || a.x > viewport.width || a.y > viewport.height;
+	});
 
 	// Show every possible spot when an imported PDF is waiting to be placed.
 	$effect(() => {
@@ -338,7 +342,7 @@
 		const fingerInks = tools.inking && settings.data.fingerDraw && !palm.penSeen;
 		// Taps on an add-page button are palm-checked like navigation: still rejected for
 		// pen-down, palm-sized contacts and right after pen use, but not for the 5 s pen session.
-		const plus = target.closest<HTMLElement>('.ghost');
+		const plus = target.closest<HTMLElement>('.ghost, .offer-pill');
 		if (e.pointerType === 'touch') {
 			const decision = palm.evaluate(e, touchIntent(fingerInks, !!plus));
 			if (!decision.accept) return; // palm: ignore entirely
@@ -707,6 +711,20 @@
 			</button>
 		{/if}
 
+		{#if offer && offerOffscreen}
+			<!-- Like the plus buttons, taps go through the palm-checked gesture. -->
+			<button
+				class="offer-pill"
+				data-anchor={offer.anchor}
+				data-dir={offer.dir}
+				data-side={offer.dir}
+				onclick={(e) => e.detail === 0 && offer && addPage(offer.anchor, offer.dir)}
+			>
+				<CirclePlusIcon size={18} strokeWidth={1.75} />
+				Add page
+			</button>
+		{/if}
+
 		{#if eraserAt && tools.tool === 'eraser'}
 			<div class="eraser-ring" style="left:{eraserAt.x}px; top:{eraserAt.y}px; width:{tools.eraserRadius * 2}px; height:{tools.eraserRadius * 2}px"></div>
 		{/if}
@@ -834,6 +852,41 @@
 			transform: scale(1.3);
 		}
 	}
+	.offer-pill {
+		position: absolute;
+		display: flex;
+		align-items: center;
+		gap: 6px;
+		padding: 10px 16px 10px 12px;
+		border: 1px solid var(--accent);
+		border-radius: 999px;
+		background: var(--bg);
+		color: var(--accent);
+		box-shadow: var(--shadow);
+		cursor: pointer;
+		white-space: nowrap;
+	}
+	.offer-pill[data-side='right'] {
+		right: 12px;
+		top: 50%;
+		transform: translateY(-50%);
+	}
+	.offer-pill[data-side='left'] {
+		left: 12px;
+		top: 50%;
+		transform: translateY(-50%);
+	}
+	.offer-pill[data-side='up'] {
+		top: 12px;
+		left: 50%;
+		transform: translateX(-50%);
+	}
+	.offer-pill[data-side='down'] {
+		/* Clear of the toolbar. */
+		bottom: 72px;
+		left: 50%;
+		transform: translateX(-50%);
+	}
 	@media (prefers-reduced-motion: reduce) {
 		.ghost.offer .plus {
 			animation: none;

src/lib/components/SettingsModal.svelte

@@ -103,6 +103,10 @@
 					<div><div class="name">Draw with finger</div><div class="desc">When off, a single finger always pans; only pen and mouse draw. Once you use a pen, fingers only pan and zoom.</div></div>
 					<input type="checkbox" class="toggle" bind:checked={s.fingerDraw} onchange={save} />
 				</div>
+				<div class="row">
+					<div><div class="name">Swipe to add pages</div><div class="desc">A quick one-finger flick toward a free side of the active page offers to add a page there.</div></div>
+					<input type="checkbox" class="toggle" bind:checked={s.flingToAdd} onchange={save} />
+				</div>
 				<h3>Palm rejection</h3>
 				<div class="row">
 					<div><div class="name">Pen session lockout</div><div class="desc">Ignore touches while the pen is writing, and finger ink for 5 seconds after it was used.</div></div>

src/lib/state/settings.svelte.ts

@@ -26,6 +26,8 @@ interface SettingsData {
 	pageStyle: PageStylePref;
 	grid: GridSettings;
 	fingerDraw: boolean;
+	/** A finger fling toward a free side of the active page offers a new page there. */
+	flingToAdd: boolean;
 	palm: PalmOptions;
 	github: GitHubSettings;
 	/** Minutes between automatic pushes (0 = manual only). */
@@ -39,6 +41,7 @@ const DEFAULTS: SettingsData = {
 	pageStyle: 'match',
 	grid: { show: true, divisions: 1 },
 	fingerDraw: true,
+	flingToAdd: true,
 	palm: DEFAULT_PALM,
 	github: { token: '', owner: '', repo: '', branch: 'main', dir: '' },
 	pushInterval: 5,