React Pinch + Zoom + Pan

README.md

Pinch + Zoom + Pan

This is a standalone pinch zoom pan React component with no other dependencies.

Demo

Open on Mobile

Features

1. Pinch to zoom
2. Breaking just out of min and max zooms and settling back
3. Double tap to reset
4. All interaction happens in the pinch zoom pan component and gets virtually computed to your underlying display.
5. Thanks to the beauty of function-as-child components, you choose how the x, y and scale are applied. I recommend CSS3 to get that sweet hardware acceleration, you know what I'm talking about?
6. Panning after zoom with limits sets by the size of the scaled content.

PinchZoomPan.js

import React from 'react';

const MIN_SCALE = 1;
const MAX_SCALE = 4;
const SETTLE_RANGE = 0.001;
const ADDITIONAL_LIMIT = 0.2;
const DOUBLE_TAP_THRESHOLD = 300;
const ANIMATION_SPEED = 0.04;
const RESET_ANIMATION_SPEED = 0.08;
const INITIAL_X = 0;
const INITIAL_Y = 0;
const INITIAL_SCALE = 1;

const settle = (val, target, range) => {
  const lowerRange = val > target - range && val < target;
  const upperRange = val < target + range && val > target;
  return lowerRange || upperRange ? target : val;
};

const inverse = (x) => -x;

const getPointFromTouch = (touch, element) => {
  const rect = element.getBoundingClientRect(); 
  return {
    x: touch.clientX - rect.left,
    y: touch.clientY - rect.top,
  };
};

const getMidpoint = (pointA, pointB) => ({
    x: (pointA.x + pointB.x) / 2.0,
    y: (pointA.y + pointB.y) / 2.0,
});

const getDistanceBetweenPoints = (pointA, pointB) => (
  Math.sqrt(Math.pow(pointA.y - pointB.y, 2) + Math.pow(pointA.x - pointB.x, 2))
);

const between = (min, max, value) => Math.min(max, Math.max(min, value));

class PinchZoomPan extends React.Component {
  constructor() {
    super(...arguments);
    this.state = this.getInititalState();

    this.handleTouchStart = this.handleTouchStart.bind(this);
    this.handleTouchMove = this.handleTouchMove.bind(this);
    this.handleTouchEnd = this.handleTouchEnd.bind(this);
  }

  zoomTo(scale, midpoint) {
    const frame = () => {
      if (this.state.scale === scale) return null;

      const distance = scale - this.state.scale;
      const targetScale = this.state.scale + (ANIMATION_SPEED * distance);

      this.zoom(settle(targetScale, scale, SETTLE_RANGE), midpoint);
      this.animation = requestAnimationFrame(frame);
    };

    this.animation = requestAnimationFrame(frame);
  }

  reset() {
    const frame = () => {
      if (this.state.scale === INITIAL_SCALE && this.state.x === INITIAL_X && this.state.y === INITIAL_Y) return null;
      const distance = INITIAL_SCALE - this.state.scale;
      const distanceX = INITIAL_X - this.state.x;
      const distanceY = INITIAL_Y - this.state.y;

      const targetScale = settle(this.state.scale + (RESET_ANIMATION_SPEED * distance), INITIAL_SCALE, SETTLE_RANGE);
      const targetX = settle(this.state.x + (RESET_ANIMATION_SPEED * distanceX), INITIAL_X, SETTLE_RANGE);
      const targetY = settle(this.state.y + (RESET_ANIMATION_SPEED * distanceY), INITIAL_Y, SETTLE_RANGE);

      const nextWidth = this.props.width * targetScale;
      const nextHeight = this.props.height * targetScale;

      this.setState({
        x: targetX,
        y: targetY,
        scale: targetScale,
        width: nextWidth,
        height: nextHeight,
      }, () => {
        this.animation = requestAnimationFrame(frame);
      });
    };

    this.animation = requestAnimationFrame(frame);
  }

  getInititalState() {
    return {
      x: INITIAL_X,
      y: INITIAL_Y,
      scale: INITIAL_SCALE,
      width: this.props.width,
      height: this.props.height,
    };
  }

  handleTouchStart(event) {
    this.animation && cancelAnimationFrame(this.animation);
    if (event.touches.length == 2) this.handlePinchStart(event);
    if (event.touches.length == 1) this.handleTapStart(event);
  }

  handleTouchMove(event) {
    if (event.touches.length == 2) this.handlePinchMove(event);
    if (event.touches.length == 1) this.handlePanMove(event);
  }

  handleTouchEnd(event) {
    if (event.touches.length > 0) return null;
    
    if (this.state.scale > MAX_SCALE) return this.zoomTo(MAX_SCALE, this.lastMidpoint);
    if (this.state.scale < MIN_SCALE) return this.zoomTo(MIN_SCALE, this.lastMidpoint);

    if (this.lastTouchEnd && this.lastTouchEnd + DOUBLE_TAP_THRESHOLD > event.timeStamp) {
      this.reset();
    }

    this.lastTouchEnd = event.timeStamp;
  }

  handleTapStart(event) {
    this.lastPanPoint = getPointFromTouch(event.touches[0], this.container);
  }

  handlePanMove(event) {
    if (this.state.scale === 1) return null;

    event.preventDefault();

    const point = getPointFromTouch(event.touches[0], this.container);
    const nextX = this.state.x + point.x - this.lastPanPoint.x;
    const nextY = this.state.y + point.y - this.lastPanPoint.y;

    this.setState({
      x: between(this.props.width - this.state.width, 0, nextX),
      y: between(this.props.height - this.state.height, 0, nextY),
    });
    
    this.lastPanPoint = point;
  }

  handlePinchStart(event) {
    const pointA = getPointFromTouch(event.touches[0], this.container);
    const pointB = getPointFromTouch(event.touches[1], this.container);
    this.lastDistance = getDistanceBetweenPoints(pointA, pointB);
  }

  handlePinchMove(event) {
    event.preventDefault();
    const pointA = getPointFromTouch(event.touches[0], this.container);
    const pointB = getPointFromTouch(event.touches[1], this.container);
    const distance = getDistanceBetweenPoints(pointA, pointB);
    const midpoint = getMidpoint(pointA, pointB);
    const scale = between(MIN_SCALE - ADDITIONAL_LIMIT, MAX_SCALE + ADDITIONAL_LIMIT, this.state.scale * (distance / this.lastDistance));

    this.zoom(scale, midpoint);

    this.lastMidpoint = midpoint;
    this.lastDistance = distance;
  }

  zoom(scale, midpoint) {
    const nextWidth = this.props.width * scale;
    const nextHeight = this.props.height * scale;
    const nextX = this.state.x + (inverse(midpoint.x * scale) * (nextWidth - this.state.width) / nextWidth);
    const nextY = this.state.y + (inverse(midpoint.y * scale) * (nextHeight - this.state.height) / nextHeight);

    this.setState({
      width: nextWidth,
      height: nextHeight,
      x: nextX,
      y: nextY,
      scale,
    });
  }

  render() {
    return (
      <div 
        ref={(ref) => this.container = ref}
        onTouchStart={this.handleTouchStart}
        onTouchMove={this.handleTouchMove}
        onTouchEnd={this.handleTouchEnd}
        style={{
          overflow: 'hidden',
          width: this.props.width,
          height: this.props.height,
        }}
      >
        {this.props.children(this.state.x, this.state.y, this.state.scale)} 
      </div>
    );
  }
}

PinchZoomPan.propTypes = {
  children: React.PropTypes.func.isRequired,
};

export default PinchZoomPan;

Usage.js

import React from 'react';

const Usage = ({width, height}) => (
  <div>
    <PinchZoomPan width={width} height={height}>
    {(x, y, scale) => (
        <img
          src={`https://placekitten.com/${width}/${height}`}
          style={{
            pointerEvents: scale === 1 ? 'auto' : 'none',
            transform: `translate3d(${x}px, ${y}px, 0) scale(${scale})`,
            transformOrigin: '0 0',
          }} />
    )}
    </PinchZoomPan>
  </div>
);

export default Usage;