Function point

A tracked point. Create via Trackers.point. Mutable. Useful for monitoring how it changes over time. Eg. when a pointerdown event happens, to record the start position and then track the pointer as it moves until pointerup.

See also

• Playground
• points: Track several points, useful for multi-touch.
• ixfx Guide to Point Tracker

import { point } from 'https://unpkg.com/ixfx/dist/trackers.js';

// Create a tracker on a pointerdown
const t = point();

// ...and later, tell it when a point is seen (eg. pointermove)
const nfo = t.seen({x: evt.x, y:evt.y});
// nfo gives us some details on the relation between the seen point, the start, and points inbetween
// nfo.angle, nfo.centroid, nfo.speed etc.
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Compute based on last seen point

t.angleFromStart();
t.distanceFromStart();
t.x / t.y
t.length; // Total length of accumulated points
t.elapsed; // Total duration since start
t.lastResult; // The PointSeenInfo for last seen point
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Housekeeping

t.reset(); // Reset tracker
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By default, the tracker only keeps track of the initial point and does not store intermediate 'seen' points. To use the tracker as a buffer, set storeIntermediate option to true.

// Keep only the last 10 points
const t = point({
 sampleLimit: 10
});

// Store all 'seen' points
const t = point({
 storeIntermediate: true
});

// In this case, the whole tracker is automatically
// reset after 10 samples
const t = point({
 resetAfterSamples: 10
})
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When using a buffer limited by sampleLimit, the 'initial' point will be the oldest in the buffer, not actually the very first point seen.