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index.js
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index.js
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class Rotator {
/**
* Main rotator class.
*/
constructor() {
/**
* Event handlers for rotation.
* @type {((this: Rotator, alpha: number) => void)[]}
*/
this.rotationHandlers = [];
/**
* The current rotation. The rotation starts right and goes counter-clockwise.
* @type {number}
*/
this.currentAlpha = 0;
/**
* If the rotator is currently in rotation state.
* @type {boolean}
*/
this.rotating = false;
/**
* The rotation when the rotation process is started.
* @type {number}
* @private
*/
this._rotationStart = 0;
/**
* The alpha of the mouse/finger when the rotation process is started.
* @type {number}
* @private
*/
this._userRotationStart = 0;
}
/**
* Attach touch events to element.
* @param {HTMLElement} element The element to add the listeners to
*/
touchEvents(element) {
/** @type {typeof HTMLElement.addEventListener} */
const on = element.on || element.addEventListener;
function calcXY(/** @type {TouchEvent} */ e) {
const centerX = element.offsetWidth / 2;
const centerY = element.offsetHeight / 2;
const relativeX = e.touches[0].clientX - element.offsetLeft;
const relativeY = e.touches[0].clientY - element.offsetTop;
return [relativeX - centerX, centerY - relativeY];
}
on("touchstart", e => {
e.preventDefault();
this.rotateStart(...calcXY(e));
});
on("touchmove", e => {
if (!this.rotating) return;
e.preventDefault();
this.rotateMove(...calcXY(e));
});
on("touchend", e => {
e.preventDefault();
this.rotateStop();
});
}
/**
* Attach touch events to element.
* @param {HTMLElement} element The element to add the listeners to
*/
mouseEvents(element) {
const on = element.on || element.addEventListener;
function calcXY(/** @type {MouseEvent} */ e) {
const centerX = element.offsetWidth / 2;
const centerY = element.offsetHeight / 2;
const relativeX = e.clientX - element.offsetLeft;
const relativeY = e.clientY - element.offsetTop;
return [relativeX - centerX, centerY - relativeY];
}
on("mousedown", e => {
e.preventDefault();
this.rotateStart(...calcXY(e));
});
on("mousemove", e => {
if (!this.rotating) return;
e.preventDefault();
this.rotateMove(...calcXY(e));
});
on("mouseup", e => {
e.preventDefault();
this.rotateStop();
});
}
/**
* Initializes the rotation process.
* Important: X and Y are values relative to the center of the object positive to top-right.
* @param {number} x X value of current position
* @param {number} y Y value of current position
*/
rotateStart(x, y) {
this.rotating = true;
this._rotationStart = this.currentAlpha;
this._userRotationStart = this._calcAlpha(x, y);
}
/**
* Rotates to the specified X and Y values relative to the starting position. Only works if rotateStart was called before.
* Important: X and Y are values relative to the center of the object positive to top-right.
* @param {number} x X value of current position
* @param {number} y Y value of current position
*/
rotateMove(x, y) {
if (!this.rotating) return;
this.currentAlpha = (this._calcAlpha(x, y) - this._userRotationStart + this._rotationStart) % 360;
this.rotationHandlers.forEach(h => h.call(this, this.currentAlpha));
}
/**
* Stops the rotation process.
*/
rotateStop() {
this.rotating = false;
this._rotationStart = 0;
this._userRotationStart = 0;
}
/**
* Calc the alpha relative to center point.
* @param {number} x
* @param {number} y
* @returns {number} Calculated alpha value
* @private
*/
_calcAlpha(x, y) {
let a = 180 * Math.atan(y / x) / Math.PI;
if (!this._isPos(x) && !this._isPos(y)) a = a + 180;
else if (!this._isPos(x) && this._isPos(y)) a += 180;
else if (this._isPos(x) && !this._isPos(y)) a += 360;
return a;
}
/**
* Check if number is positive.
* @param {number} num
* @returns {boolean} If number is positive
* @private
*/
_isPos(num) {
return num == Math.abs(num);
}
/**
* Add a new rotation handler to the list. Will be executed when the element is rotated.
* @param {(this: Rotator, alpha: number) => void} func Event handler
*/
addRotationHandler(func) {
this.rotationHandlers.push(func);
}
/**
* Removes a rotation handler from the list.
* @param {(this: Rotator, alpha: number) => void} func Event handler
*/
removeRotationHandler(func) {
const index = this.rotationHandlers.indexOf(func);
if (index > -1) this.rotationHandlers.splice(index, 1);
}
/**
* Add all events to the specified element.
* @param {HTMLElement|string} element The element to use
* @returns {Rotator} The generated rotator
*/
static hookToElement(element) {
if (typeof element == "string") {
element = document.getElementById(element) || document.querySelector(element);
}
const rotator = new Rotator();
rotator.touchEvents(element);
rotator.mouseEvents(element);
rotator.addRotationHandler(alpha => {
element.style.transform = `rotate(${(0 - alpha).toFixed(2)}deg)`;
element.style.transformOrigin = "center center";
});
return rotator;
}
}