added usePinchZoom sensor hook

Author: Abhishek Mittal

README.md

@@ -77,6 +77,7 @@
   - [`useMeasure`](./docs/useMeasure.md) and [`useSize`](./docs/useSize.md) — tracks an HTML element's dimensions. [![][img-demo]](https://streamich.github.io/react-use/?path=/story/sensors-usemeasure--demo)
   - [`createBreakpoint`](./docs/createBreakpoint.md) — tracks `innerWidth`
   - [`useScrollbarWidth`](./docs/useScrollbarWidth.md) — detects browser's native scrollbars width. [![][img-demo]](https://streamich.github.io/react-use/?path=/story/sensors-usescrollbarwidth--demo)
+  - [`usePinchZoom`](./docs/usePinchZoom.md) — tracks pointer events to detect pinch zoom in and out status. [![][img-demo]](https://streamich.github.io/react-use/?path=/story/sensors-usePinchZoom--demo)
     <br/>
     <br/>
 - [**UI**](./docs/UI.md)

docs/usePinchZoom.md

@@ -0,0 +1,36 @@
+# `usePinchZoon`
+
+React sensor hook that tracks the changes in pointer touch events and detects value of pinch difference and tell if user is zooming in or out.
+
+## Usage
+
+```jsx
+import { usePinchZoon } from "react-use";
+
+const Demo = () => {
+  const [scale, setState] = useState(1);
+  const scaleRef = useRef();
+  const { zoomingState, pinchState } = usePinchZoom(scaleRef);
+
+  useEffect(() => {
+    if (zoomingState === "ZOOM_IN") {
+      // perform zoom in scaling
+      setState(scale + 0.1)
+    } else if (zoomingState === "ZOOM_OUT") {
+      // perform zoom out in scaling
+      setState(scale - 0.1)
+    }
+  }, [zoomingState]);
+
+  return (
+    <div ref={scaleRef}>
+      <img
+        src="https://www.olympus-imaging.co.in/content/000107506.jpg"
+        style={{
+          zoom: scale,
+        }}
+      />
+    </div>
+  );
+};
+```

src/index.ts

@@ -109,6 +109,7 @@ export { useMultiStateValidator } from './useMultiStateValidator';
 export { default as useWindowScroll } from './useWindowScroll';
 export { default as useWindowSize } from './useWindowSize';
 export { default as useMeasure } from './useMeasure';
+export { default as usePinchZoom } from './usePinchZoom';
 export { useRendersCount } from './useRendersCount';
 export { useFirstMountState } from './useFirstMountState';
 export { default as useSet } from './useSet';

src/usePinchZoom.ts

@@ -0,0 +1,109 @@
+import { RefObject, useEffect, useMemo, useState } from 'react';
+
+export type CacheRef = {
+  prevDiff: number;
+  evCache: Array<PointerEvent>;
+};
+
+export enum ZoomState {
+  'ZOOMING_IN' = 'ZOOMING_IN',
+  'ZOOMING_OUT' = 'ZOOMING_OUT',
+}
+
+export type ZoomStateType = ZoomState.ZOOMING_IN | ZoomState.ZOOMING_OUT;
+
+const usePinchZoom = (ref: RefObject<HTMLElement>) => {
+  const cacheRef = useMemo<CacheRef>(
+    () => ({
+      evCache: [],
+      prevDiff: -1,
+    }),
+    [ref.current]
+  );
+
+  const [zoomingState, setZoomingState] = useState<[ZoomStateType, number]>();
+
+  const pointermove_handler = (ev: PointerEvent) => {
+    // This function implements a 2-pointer horizontal pinch/zoom gesture.
+    //
+    // If the distance between the two pointers has increased (zoom in),
+    // the target element's background is changed to 'pink' and if the
+    // distance is decreasing (zoom out), the color is changed to 'lightblue'.
+    //
+    // This function sets the target element's border to 'dashed' to visually
+    // indicate the pointer's target received a move event.
+    // Find this event in the cache and update its record with this event
+    for (let i = 0; i < cacheRef.evCache.length; i++) {
+      if (ev.pointerId == cacheRef.evCache[i].pointerId) {
+        cacheRef.evCache[i] = ev;
+        break;
+      }
+    }
+
+    // If two pointers are down, check for pinch gestures
+    if (cacheRef.evCache.length == 2) {
+      // console.log(prevDiff)
+      // Calculate the distance between the two pointers
+      const curDiff = Math.abs(cacheRef.evCache[0].clientX - cacheRef.evCache[1].clientX);
+
+      if (cacheRef.prevDiff > 0) {
+        if (curDiff > cacheRef.prevDiff) {
+          // The distance between the two pointers has increased
+          setZoomingState([ZoomState.ZOOMING_IN, curDiff]);
+        }
+        if (curDiff < cacheRef.prevDiff) {
+          // The distance between the two pointers has decreased
+          setZoomingState([ZoomState.ZOOMING_OUT, curDiff]);
+        }
+      }
+
+      // Cache the distance for the next move event
+      cacheRef.prevDiff = curDiff;
+    }
+  };
+
+  const pointerdown_handler = (ev: PointerEvent) => {
+    // The pointerdown event signals the start of a touch interaction.
+    // This event is cached to support 2-finger gestures
+    cacheRef.evCache.push(ev);
+    // console.log('pointerDown', ev);
+  };
+
+  const pointerup_handler = (ev: PointerEvent) => {
+    // Remove this pointer from the cache and reset the target's
+    // background and border
+    remove_event(ev);
+
+    // If the number of pointers down is less than two then reset diff tracker
+    if (cacheRef.evCache.length < 2) {
+      cacheRef.prevDiff = -1;
+    }
+  };
+
+  const remove_event = (ev: PointerEvent) => {
+    // Remove this event from the target's cache
+    for (let i = 0; i < cacheRef.evCache.length; i++) {
+      if (cacheRef.evCache[i].pointerId == ev.pointerId) {
+        cacheRef.evCache.splice(i, 1);
+        break;
+      }
+    }
+  };
+
+  useEffect(() => {
+    if (ref?.current) {
+      ref.current.onpointerdown = pointerdown_handler;
+      ref.current.onpointermove = pointermove_handler;
+      ref.current.onpointerup = pointerup_handler;
+      ref.current.onpointercancel = pointerup_handler;
+      ref.current.onpointerout = pointerup_handler;
+      ref.current.onpointerleave = pointerup_handler;
+    }
+  }, [ref?.current]);
+
+  return zoomingState
+    ? { zoomingState: zoomingState[0], pinchState: zoomingState[1] }
+    : { zoomingState: null, pinchState: 0 };
+};
+
+export default usePinchZoom;

stories/usePinchZoom.story.tsx

@@ -0,0 +1,37 @@
+import { storiesOf } from '@storybook/react';
+import { useEffect, useRef, useState } from 'react';
+import { usePinchZoom } from '../src';
+import { ZoomState } from '../src/usePinchZoom';
+import ShowDocs from './util/ShowDocs';
+
+const Demo = () => {
+  const [scale, setState] = useState(1);
+  const scaleRef = useRef();
+  const { zoomingState, pinchState } = usePinchZoom(scaleRef);
+
+  useEffect(() => {
+    if (zoomingState === ZoomState.ZOOMING_IN) {
+      // perform zoom in scaling
+      setState(scale + 0.1);
+    } else if (zoomingState === ZoomState.ZOOMING_OUT) {
+      // perform zoom out in scaling
+      setState(scale - 0.1);
+    }
+  }, [zoomingState, pinchState]);
+
+  return (
+    <div ref={scaleRef}>
+      <img
+        src="https://www.olympus-imaging.co.in/content/000107506.jpg"
+        style={{
+          zoom: scale,
+        }}
+        alt="scale img"
+      />
+    </div>
+  );
+};
+
+storiesOf('Sensors/usePinchZoom', module)
+  .add('Docs', () => <ShowDocs md={require('../docs/usePinchZoom.md')} />)
+  .add('Default', () => <Demo />);