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5a501a5c87
A quick one-finger flick toward a free side of the active page, once that edge is on screen, highlights and pulses the plus button on that side for three seconds. It never adds a page by itself, so ordinary panning can't create pages; a tap on the highlighted plus does. Fling detection lives in ink/fling.ts with tests. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GaoZtJQZwLXkEgWs8twCia
41 lines
1.3 KiB
TypeScript
41 lines
1.3 KiB
TypeScript
// Fling detection for one-finger pans: a quick flick that ends the drag.
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import type { Dir } from '$lib/model/tree';
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export interface Sample {
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x: number;
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y: number;
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t: number;
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}
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/** Only the last stretch of the drag counts. */
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const WINDOW_MS = 100;
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/** px/ms; a slow drag that stops is not a fling. */
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const MIN_SPEED = 0.6;
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/** The main axis must dominate by this much. */
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const MIN_RATIO = 2;
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/**
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* Side of the canvas a fling heads for, or null. Moving the finger left pulls in
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* what's on the right, so a leftward flick returns 'right'.
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*/
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export function flingDir(samples: readonly Sample[]): Dir | null {
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const last = samples.at(-1);
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if (!last) return null;
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const first = samples.find((s) => last.t - s.t <= WINDOW_MS);
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if (!first || first === last) return null;
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const dt = last.t - first.t;
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if (dt <= 0) return null;
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const dx = last.x - first.x;
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const dy = last.y - first.y;
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if (Math.hypot(dx, dy) / dt < MIN_SPEED) return null;
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if (Math.abs(dx) >= Math.abs(dy) * MIN_RATIO) return dx < 0 ? 'right' : 'left';
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if (Math.abs(dy) >= Math.abs(dx) * MIN_RATIO) return dy < 0 ? 'down' : 'up';
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return null;
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}
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/** Keeps a short trail of pointer samples for flingDir. */
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export function pushSample(samples: Sample[], s: Sample) {
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samples.push(s);
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while (samples.length > 2 && s.t - samples[0].t > WINDOW_MS * 2) samples.shift();
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}
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