verdnatura-chat/app/presentation/ImageViewer/index.android.js

import React from 'react';
import { StyleSheet, View } from 'react-native';
import PropTypes from 'prop-types';
import {
	PanGestureHandler,
	State,
	PinchGestureHandler
} from 'react-native-gesture-handler';
import FastImage from 'react-native-fast-image';
import Animated, { Easing } from 'react-native-reanimated';
import { ResponsiveComponent } from 'react-native-responsive-ui';

const AnimatedFastImage = Animated.createAnimatedComponent(FastImage);

const styles = StyleSheet.create({
	wrapper: {
		flex: 1
	},
	image: {
		backgroundColor: 'transparent'
	}
});

const {
	set,
	cond,
	eq,
	or,
	add,
	sub,
	min,
	max,
	multiply,
	divide,
	lessThan,
	decay,
	timing,
	diff,
	not,
	abs,
	startClock,
	stopClock,
	clockRunning,
	Value,
	Clock,
	event
} = Animated;

function scaleDiff(value) {
	const tmp = new Value(1);
	const prev = new Value(1);
	return [set(tmp, divide(value, prev)), set(prev, value), tmp];
}

function dragDiff(value, updating) {
	const tmp = new Value(0);
	const prev = new Value(0);
	return cond(
		updating,
		[set(tmp, sub(value, prev)), set(prev, value), tmp],
		set(prev, 0)
	);
}

// returns linear friction coeff. When `value` is 0 coeff is 1 (no friction), then
// it grows linearly until it reaches `MAX_FRICTION` when `value` is equal
// to `MAX_VALUE`
function friction(value) {
	const MAX_FRICTION = 5;
	const MAX_VALUE = 100;
	return max(
		1,
		min(MAX_FRICTION, add(1, multiply(value, (MAX_FRICTION - 1) / MAX_VALUE)))
	);
}

function speed(value) {
	const clock = new Clock();
	const dt = diff(clock);
	return cond(lessThan(dt, 1), 0, multiply(1000, divide(diff(value), dt)));
}

const MIN_SCALE = 1;
const MAX_SCALE = 2;

function scaleRest(value) {
	return cond(
		lessThan(value, MIN_SCALE),
		MIN_SCALE,
		cond(lessThan(MAX_SCALE, value), MAX_SCALE, value)
	);
}

function scaleFriction(value, rest, delta) {
	const MAX_FRICTION = 20;
	const MAX_VALUE = 0.5;
	const res = multiply(value, delta);
	const howFar = abs(sub(rest, value));
	const f = max(
		1,
		min(MAX_FRICTION, add(1, multiply(howFar, (MAX_FRICTION - 1) / MAX_VALUE)))
	);
	return cond(
		lessThan(0, howFar),
		multiply(value, add(1, divide(add(delta, -1), f))),
		res
	);
}

function runTiming(clock, value, dest, startStopClock = true) {
	const state = {
		finished: new Value(0),
		position: new Value(0),
		frameTime: new Value(0),
		time: new Value(0)
	};

	const config = {
		toValue: new Value(0),
		duration: 300,
		easing: Easing.inOut(Easing.cubic)
	};

	return [
		cond(clockRunning(clock), 0, [
			set(state.finished, 0),
			set(state.frameTime, 0),
			set(state.time, 0),
			set(state.position, value),
			set(config.toValue, dest),
			startStopClock && startClock(clock)
		]),
		timing(clock, state, config),
		cond(state.finished, startStopClock && stopClock(clock)),
		state.position
	];
}

function runDecay(clock, value, velocity) {
	const state = {
		finished: new Value(0),
		velocity: new Value(0),
		position: new Value(0),
		time: new Value(0)
	};

	const config = { deceleration: 0.99 };

	return [
		cond(clockRunning(clock), 0, [
			set(state.finished, 0),
			set(state.velocity, velocity),
			set(state.position, value),
			set(state.time, 0),
			startClock(clock)
		]),
		set(state.position, value),
		decay(clock, state, config),
		cond(state.finished, stopClock(clock)),
		state.position
	];
}

function bouncyPinch(
	value,
	gesture,
	gestureActive,
	focalX,
	displacementX,
	focalY,
	displacementY
) {
	const clock = new Clock();

	const delta = scaleDiff(gesture);
	const rest = scaleRest(value);
	const focalXRest = cond(
		lessThan(value, 1),
		0,
		sub(displacementX, multiply(focalX, add(-1, divide(rest, value))))
	);
	const focalYRest = cond(
		lessThan(value, 1),
		0,
		sub(displacementY, multiply(focalY, add(-1, divide(rest, value))))
	);
	const nextScale = new Value(1);

	return cond(
		[delta, gestureActive],
		[
			stopClock(clock),
			set(nextScale, scaleFriction(value, rest, delta)),
			set(
				displacementX,
				sub(displacementX, multiply(focalX, add(-1, divide(nextScale, value))))
			),
			set(
				displacementY,
				sub(displacementY, multiply(focalY, add(-1, divide(nextScale, value))))
			),
			nextScale
		],
		cond(
			or(clockRunning(clock), not(eq(rest, value))),
			[
				set(displacementX, runTiming(clock, displacementX, focalXRest, false)),
				set(displacementY, runTiming(clock, displacementY, focalYRest, false)),
				runTiming(clock, value, rest)
			],
			value
		)
	);
}

function bouncy(
	value,
	gestureDiv,
	gestureActive,
	lowerBound,
	upperBound,
	f
) {
	const timingClock = new Clock();
	const decayClock = new Clock();

	const velocity = speed(value);

	// did value go beyond the limits (lower, upper)
	const isOutOfBounds = or(
		lessThan(value, lowerBound),
		lessThan(upperBound, value)
	);
	// position to snap to (upper or lower is beyond or the current value elsewhere)
	const rest = cond(
		lessThan(value, lowerBound),
		lowerBound,
		cond(lessThan(upperBound, value), upperBound, value)
	);
	// how much the value exceeds the bounds, this is used to calculate friction
	const outOfBounds = abs(sub(rest, value));

	return cond(
		[gestureDiv, velocity, gestureActive],
		[
			stopClock(timingClock),
			stopClock(decayClock),
			add(value, divide(gestureDiv, f(outOfBounds)))
		],
		cond(
			or(clockRunning(timingClock), isOutOfBounds),
			[stopClock(decayClock), runTiming(timingClock, value, rest)],
			cond(
				or(clockRunning(decayClock), lessThan(5, abs(velocity))),
				runDecay(decayClock, value, velocity),
				value
			)
		)
	);
}

const WIDTH = 300;
const HEIGHT = 300;

// it was picked from https://github.com/software-mansion/react-native-reanimated/tree/master/Example/imageViewer
// and changed to use FastImage animated component
class ImageViewer extends ResponsiveComponent {
	pinchRef = React.createRef();

	panRef = React.createRef();

	static propTypes = {
		uri: PropTypes.string
	}

	constructor(props) {
		super(props);

		// DECLARE TRANSX
		const panTransX = new Value(0);
		const panTransY = new Value(0);

		// PINCH
		const pinchScale = new Value(1);
		const pinchFocalX = new Value(0);
		const pinchFocalY = new Value(0);
		const pinchState = new Value(-1);

		this._onPinchEvent = event([
			{
				nativeEvent: {
					state: pinchState,
					scale: pinchScale,
					focalX: pinchFocalX,
					focalY: pinchFocalY
				}
			}
		]);

		// SCALE
		const scale = new Value(1);
		const pinchActive = eq(pinchState, State.ACTIVE);
		this._focalDisplacementX = new Value(0);
		const relativeFocalX = sub(
			pinchFocalX,
			add(panTransX, this._focalDisplacementX)
		);
		this._focalDisplacementY = new Value(0);
		const relativeFocalY = sub(
			pinchFocalY,
			add(panTransY, this._focalDisplacementY)
		);
		this._scale = set(
			scale,
			bouncyPinch(
				scale,
				pinchScale,
				pinchActive,
				relativeFocalX,
				this._focalDisplacementX,
				relativeFocalY,
				this._focalDisplacementY
			)
		);

		// PAN
		const dragX = new Value(0);
		const dragY = new Value(0);
		const panState = new Value(-1);
		this._onPanEvent = event([
			{
				nativeEvent: {
					translationX: dragX,
					translationY: dragY,
					state: panState
				}
			}
		]);

		const panActive = eq(panState, State.ACTIVE);
		const panFriction = value => friction(value);

		// X
		const panUpX = cond(
			lessThan(this._scale, 1),
			0,
			multiply(-1, this._focalDisplacementX)
		);
		const panLowX = add(panUpX, multiply(-WIDTH, add(max(1, this._scale), -1)));
		this._panTransX = set(
			panTransX,
			bouncy(
				panTransX,
				dragDiff(dragX, panActive),
				or(panActive, pinchActive),
				panLowX,
				panUpX,
				panFriction
			)
		);

		// Y
		const panUpY = cond(
			lessThan(this._scale, 1),
			0,
			multiply(-1, this._focalDisplacementY)
		);
		const panLowY = add(
			panUpY,
			multiply(-HEIGHT, add(max(1, this._scale), -1))
		);
		this._panTransY = set(
			panTransY,
			bouncy(
				panTransY,
				dragDiff(dragY, panActive),
				or(panActive, pinchActive),
				panLowY,
				panUpY,
				panFriction
			)
		);
	}

	render() {
		const { uri, ...props } = this.props;
		const { width } = this.state.window;

		// The below two animated values makes it so that scale appears to be done
		// from the top left corner of the image view instead of its center. This
		// is required for the "scale focal point" math to work correctly
		const scaleTopLeftFixX = divide(multiply(WIDTH, add(this._scale, -1)), 2);
		const scaleTopLeftFixY = divide(multiply(HEIGHT, add(this._scale, -1)), 2);
		return (
			<View style={styles.wrapper}>
				<PinchGestureHandler
					ref={this.pinchRef}
					simultaneousHandlers={this.panRef}
					onGestureEvent={this._onPinchEvent}
					onHandlerStateChange={this._onPinchEvent}
				>
					<Animated.View>
						<PanGestureHandler
							ref={this.panRef}
							minDist={10}
							avgTouches
							simultaneousHandlers={this.pinchRef}
							onGestureEvent={this._onPanEvent}
							onHandlerStateChange={this._onPanEvent}
						>
							<AnimatedFastImage
								style={[
									styles.image,
									{
										width,
										height: '100%'
									},
									{
										transform: [
											{ translateX: this._panTransX },
											{ translateY: this._panTransY },
											{ translateX: this._focalDisplacementX },
											{ translateY: this._focalDisplacementY },
											{ translateX: scaleTopLeftFixX },
											{ translateY: scaleTopLeftFixY },
											{ scale: this._scale }
										]
									}
								]}
								resizeMode='contain'
								source={{ uri }}
								{...props}
							/>
						</PanGestureHandler>
					</Animated.View>
				</PinchGestureHandler>
			</View>
		);
	}
}

export default ImageViewer;