@shopify/flash-list
Version:
FlashList is a more performant FlatList replacement
70 lines • 2.74 kB
JavaScript
;
Object.defineProperty(exports, "__esModule", { value: true });
exports.VelocityTracker = void 0;
/**
* Tracks and calculates velocity for scroll/drag movements
* Used to determine momentum scrolling behavior
*/
var VelocityTracker = /** @class */ (function () {
function VelocityTracker() {
/** Timestamp of the last velocity update */
this.lastUpdateTime = Date.now();
/** Current velocity vector with x and y components */
this.velocity = { x: 0, y: 0 };
/** Reference to the momentum end timeout */
this.timeoutId = null;
}
/**
* Calculates velocity based on position change over time
* @param newOffset Current position value
* @param oldOffset Previous position value
* @param isHorizontal Whether movement is horizontal (true) or vertical (false)
* @param isRTL Whether layout direction is right-to-left
* @param callback Function to call with velocity updates and momentum end signal
*/
VelocityTracker.prototype.computeVelocity = function (newOffset, oldOffset, isHorizontal, callback) {
var _this = this;
// Clear any pending momentum end timeout
this.cleanUp();
// Calculate time since last update
var currentTime = Date.now();
var timeSinceLastUpdate = Math.max(1, currentTime - this.lastUpdateTime);
// Calculate velocity as distance/time
var newVelocity = (newOffset - oldOffset) / timeSinceLastUpdate;
// console.log(
// "newVelocity",
// newOffset,
// oldOffset,
// currentTime,
// this.lastUpdateTime,
// timeSinceLastUpdate,
// newVelocity
// );
this.lastUpdateTime = currentTime;
// Apply velocity to the correct axis
this.velocity.x = isHorizontal ? newVelocity : 0;
this.velocity.y = isHorizontal ? 0 : newVelocity;
// Trigger callback with current velocity
callback(this.velocity, false);
// Set timeout to signal momentum end after 100ms of no updates
this.timeoutId = setTimeout(function () {
_this.cleanUp();
_this.lastUpdateTime = Date.now();
_this.velocity.x = 0;
_this.velocity.y = 0;
callback(_this.velocity, true);
}, 100);
};
/**
* Cleans up resources by clearing any pending timeout
*/
VelocityTracker.prototype.cleanUp = function () {
if (this.timeoutId !== null) {
clearTimeout(this.timeoutId);
this.timeoutId = null;
}
};
return VelocityTracker;
}());
exports.VelocityTracker = VelocityTracker;
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