Puppeteer drives a multi-finger gesture with one TouchHandle per finger

Fact

page.touchscreen.touchStart(x, y) returns a TouchHandle; its move() and end() move or lift that finger alone while the others stay down. That covers pinches, a third finger joining, and lifting one finger of two first. The events arrive as trusted pointerType: 'touch' pointer events without any hasTouch emulation.

Underneath, each call sends CDP Input.dispatchTouchEvent with only its own point, touchEnd included, although the protocol's description says touchEnd "must not contain any touch points". In raw CDP, a touchMove that leaves a finger out does not lift it; a touchEnd lifts exactly the points it lists, and an empty one lifts every finger.

Why it matters

Going by the protocol text, a raw-CDP test sends touchMove without the finger it means to lift ("one event per changed point, compared to the previous event"); the finger stays down, and the test silently keeps pinching.

How to apply

const one = await page.touchscreen.touchStart(100, 200);
const two = await page.touchscreen.touchStart(160, 200);
for (let i = 1; i <= 20; i++) {
  await one.move(100 - i * 3, 200);
  await two.move(160 + i * 3, 200);
}
await two.end(); // the first finger is still down
await one.move(130, 200);
await one.end();

Each move() is its own event, so one step of a pinch arrives as two pointermoves. Coordinates are rounded to whole pixels.

Related: [[puppeteer-touch-move-resolves-before-the-page-handles-it]], [[setpointercapture-throws-for-inactive-pointer-id]].