react-native-screen-transitions/src/utils/gesture/apply-offset-rules.ts

Easy screen transitions for React Native and Expo

import type { ScaledSize } from "react-native";
import type { GestureStateManagerType } from "react-native-gesture-handler/lib/typescript/handlers/gestures/gestureStateManager";
import type { SharedValue } from "react-native-reanimated";
import {
	DEFAULT_ACTIVATION_AREA,
	DEFAULT_EDGE_DISTANCE_HORIZONTAL,
	DEFAULT_EDGE_DISTANCE_VERTICAL,
	GESTURE_ACTIVATION_THRESHOLD_X,
	GESTURE_ACTIVATION_THRESHOLD_Y,
	GESTURE_FAIL_TOLERANCE_X,
	GESTURE_FAIL_TOLERANCE_Y,
} from "../../constants";
import {
	type ActivationArea,
	type GestureActivationArea,
	GestureOffsetState,
	type SideActivation,
} from "../../types/gesture";

type Directions = {
	vertical: boolean;
	verticalInverted: boolean;
	horizontal: boolean;
	horizontalInverted: boolean;
};

interface CheckGestureActivationProps {
	initialTouch: { x: number; y: number };
	touch: { x: number; y: number };
	directions: Directions;
	manager?: GestureStateManagerType;
	gestureOffsetState: SharedValue<GestureOffsetState>;
	activationArea?: GestureActivationArea;
	dimensions: ScaledSize;
	responseDistance?: number;
}

type NormalizedSides = {
	left: ActivationArea;
	right: ActivationArea;
	top: ActivationArea;
	bottom: ActivationArea;
};

interface ShouldActivateOrFailProps {
	deltaX: number;
	deltaY: number;
	hasHorizontal: boolean;
	hasVertical: boolean;
	isHorizontalSwipe: boolean;
	isVerticalSwipe: boolean;
	allowedRight: boolean;
	allowedLeft: boolean;
	allowedUp: boolean;
	allowedDown: boolean;
	horizontalGateRight: boolean;
	horizontalGateLeft: boolean;
	verticalGateUp: boolean;
	verticalGateDown: boolean;
	isSwipingRight: boolean;
	isSwipingLeft: boolean;
	isSwipingUp: boolean;
	isSwipingDown: boolean;
}

interface ReturnValues {
	isSwipingDown: boolean;
	isSwipingUp: boolean;
	isSwipingRight: boolean;
	isSwipingLeft: boolean;
}

function normalizeSides(area?: GestureActivationArea): NormalizedSides {
	"worklet";
	if (!area || typeof area === "string") {
		const mode: ActivationArea = area ?? DEFAULT_ACTIVATION_AREA;
		return { left: mode, right: mode, top: mode, bottom: mode };
	}

	const s: SideActivation = area as SideActivation;
	return {
		left: s.left ?? DEFAULT_ACTIVATION_AREA,
		right: s.right ?? DEFAULT_ACTIVATION_AREA,
		top: s.top ?? DEFAULT_ACTIVATION_AREA,
		bottom: s.bottom ?? DEFAULT_ACTIVATION_AREA,
	};
}

function computeEdgeConstraints(
	initialTouch: { x: number; y: number },
	dimensions: ScaledSize,
	sides: NormalizedSides,
	responseDistance?: number,
) {
	"worklet";
	const xDist = responseDistance ?? DEFAULT_EDGE_DISTANCE_HORIZONTAL;
	const yDist = responseDistance ?? DEFAULT_EDGE_DISTANCE_VERTICAL;

	const horizontalRight = sides.left === "screen" || initialTouch.x <= xDist; // right swipe checks left edge
	const horizontalLeft =
		sides.right === "screen" || initialTouch.x >= dimensions.width - xDist; // left swipe checks right edge
	const verticalDown = sides.top === "screen" || initialTouch.y <= yDist; // down swipe checks top edge
	const verticalUp =
		sides.bottom === "screen" || initialTouch.y >= dimensions.height - yDist; // up swipe checks bottom edge

	return { horizontalRight, horizontalLeft, verticalDown, verticalUp } as const;
}

function calculateSwipeDirs(deltaX: number, deltaY: number) {
	"worklet";

	const isVerticalSwipe = Math.abs(deltaY) > Math.abs(deltaX);
	const isHorizontalSwipe = Math.abs(deltaX) > Math.abs(deltaY);

	const isSwipingDown = isVerticalSwipe && deltaY > 0;
	const isSwipingUp = isVerticalSwipe && deltaY < 0;
	const isSwipingRight = isHorizontalSwipe && deltaX > 0;
	const isSwipingLeft = isHorizontalSwipe && deltaX < 0;

	return {
		isSwipingDown,
		isSwipingUp,
		isSwipingRight,
		isSwipingLeft,
		isVerticalSwipe,
		isHorizontalSwipe,
	};
}

function shouldActivateOrFail(params: ShouldActivateOrFailProps) {
	"worklet";

	const {
		deltaX,
		deltaY,
		hasHorizontal,
		hasVertical,
		isHorizontalSwipe,
		isVerticalSwipe,
		allowedRight,
		allowedLeft,
		allowedUp,
		allowedDown,
		horizontalGateRight,
		horizontalGateLeft,
		verticalGateUp,
		verticalGateDown,
		isSwipingRight,
		isSwipingLeft,
		isSwipingUp,
		isSwipingDown,
	} = params;

	let shouldActivate = false;
	let shouldFail = false;

	if (hasHorizontal && isHorizontalSwipe) {
		const hasEnoughHorizontalMovement =
			Math.abs(deltaX) >= GESTURE_ACTIVATION_THRESHOLD_X;

		const hasAcceptableVerticalDeviation =
			Math.abs(deltaY) <= GESTURE_FAIL_TOLERANCE_X;

		if (hasEnoughHorizontalMovement && hasAcceptableVerticalDeviation) {
			const rightOk = isSwipingRight && allowedRight && horizontalGateRight;
			const leftOk = isSwipingLeft && allowedLeft && horizontalGateLeft;
			if (rightOk || leftOk) {
				shouldActivate = true;
			}
		} else if (!hasAcceptableVerticalDeviation) {
			shouldFail = true;
		}
	}

	if (hasVertical && isVerticalSwipe) {
		const hasEnoughVerticalMovement =
			Math.abs(deltaY) >= GESTURE_ACTIVATION_THRESHOLD_Y;
		const hasAcceptableHorizontalDeviation =
			Math.abs(deltaX) <= GESTURE_FAIL_TOLERANCE_Y;

		if (hasEnoughVerticalMovement && hasAcceptableHorizontalDeviation) {
			const upOk = isSwipingUp && allowedUp && verticalGateUp;
			const downOk = isSwipingDown && allowedDown && verticalGateDown;
			if (upOk || downOk) {
				shouldActivate = true;
			}
		} else if (!hasAcceptableHorizontalDeviation) {
			shouldFail = true;
		}
	}

	if (hasHorizontal && isHorizontalSwipe) {
		if ((isSwipingLeft && !allowedLeft) || (isSwipingRight && !allowedRight)) {
			shouldFail = true;
		}
		// If gating prohibits the dominant horizontal swipe, fail early
		if (
			(isSwipingRight && allowedRight && !horizontalGateRight) ||
			(isSwipingLeft && allowedLeft && !horizontalGateLeft)
		) {
			shouldFail = true;
		}
	}

	if (hasVertical && isVerticalSwipe) {
		if ((isSwipingUp && !allowedUp) || (isSwipingDown && !allowedDown)) {
			shouldFail = true;
		}
		// If gating prohibits the dominant vertical swipe, fail early
		if (
			(isSwipingUp && allowedUp && !verticalGateUp) ||
			(isSwipingDown && allowedDown && !verticalGateDown)
		) {
			shouldFail = true;
		}
	}

	return { shouldActivate, shouldFail };
}

/**
 * Since we're using onTouchesMove to activate our pan, faillOffset and activateOffset don't actually work. In that case we'll create this function to use in onTouchesMove which acts simarly to the original functionality.
 */
export const applyOffsetRules = ({
	initialTouch,
	touch,
	directions,
	manager,
	gestureOffsetState,
	activationArea,
	dimensions,
	responseDistance,
}: CheckGestureActivationProps): ReturnValues => {
	"worklet";

	const deltaX = touch.x - initialTouch.x;
	const deltaY = touch.y - initialTouch.y;

	const allowedDown = directions.vertical;
	const allowedUp = directions.verticalInverted;
	const allowedRight = directions.horizontal;
	const allowedLeft = directions.horizontalInverted;

	const hasHorizontal = allowedLeft || allowedRight;
	const hasVertical = allowedUp || allowedDown;

	const {
		isSwipingDown,
		isSwipingUp,
		isSwipingRight,
		isSwipingLeft,
		isVerticalSwipe,
		isHorizontalSwipe,
	} = calculateSwipeDirs(deltaX, deltaY);

	// avoid re-running the function if the activation state is already set
	if (
		gestureOffsetState.value === GestureOffsetState.PASSED ||
		gestureOffsetState.value === GestureOffsetState.FAILED
	) {
		return {
			isSwipingDown,
			isSwipingUp,
			isSwipingRight,
			isSwipingLeft,
		};
	}

	const sides = normalizeSides(activationArea);

	const {
		horizontalRight: horizontalGateRight,
		horizontalLeft: horizontalGateLeft,
		verticalDown: verticalGateDown,
		verticalUp: verticalGateUp,
	} = computeEdgeConstraints(initialTouch, dimensions, sides, responseDistance);

	const { shouldActivate, shouldFail } = shouldActivateOrFail({
		deltaX,
		deltaY,
		hasHorizontal,
		hasVertical,
		isHorizontalSwipe,
		isVerticalSwipe,
		allowedRight,
		allowedLeft,
		allowedUp,
		allowedDown,
		horizontalGateRight,
		horizontalGateLeft,
		verticalGateUp,
		verticalGateDown,
		isSwipingRight,
		isSwipingLeft,
		isSwipingUp,
		isSwipingDown,
	});

	if (shouldActivate) {
		gestureOffsetState.value = GestureOffsetState.PASSED;
	} else if (shouldFail) {
		gestureOffsetState.value = GestureOffsetState.FAILED;
		manager?.fail();
	}

	return {
		isSwipingDown,
		isSwipingUp,
		isSwipingRight,
		isSwipingLeft,
	};
};