Quantpos

Quantpos makes FLIP (First Last Invert Play) simple !

It handles all the transform part of the FLIP method.

npm package : https://www.npmjs.com/package/quantpos

github repo : https://github.com/hl037/quantpos

Usage

The main usage of this library is to move an html element at another place in the DOM while retaining its graphical position.

1) Import the relevant functions :

import {getGlobalMat, setGlobalMat} from 'quantpos'

2) Get the global matrix of your element

// let el = document.getElementById('my-el')
let mat = getGlobalMat(el)

3) Move your element somewhere else in the dom

(Using either method you want)

4) Set the global position you retained earlier

// let el = document.getElementById('my-el')
setGlobalMat(el, mat)

And you're done !

(See Advanced pattern for FLIP animation)

Install

one of these three commands :

npm install quantpos

pnpm add quantpos

yarn add quantpos

...You know better than me =)

API from rematrix

The matrix class is from rematrix https://github.com/jlmakes/rematrix

All rematrix functions are forward-exported.

The following functions are patches or additions :

type Coords

type Coords2D = [number, number]
type Coords3D = [number, number, number]
type Coords4D = [number, number, number, number]
type Coords = Coords2D | Coords3D | Coords4D

apply(m:Matrix, x:Coords): Coords4D

Apply a matrix to a vector (matrix multiplication with a vector) NOTE : The result is not normalized (the 4th coordinate may not be 1). Call normalize() on the result if you want to use it (as an optimization, you can chain matrix multiplications before normalizing though).

normalize(x:Coords): Coords4D

Normalize a vector x. This function always returns a Coords4D. If a Coords2D or Coords3D are passed, it returns the same vector with 4th coordinate set to 1 and 3rd to 0 if not provided.

translate(...x:[Coords]|number[]): M.Matrix3D

Create a translation matrix for x. This deffers from the rematrix implementation because this one function handles all thes cases. You can either pass an array (Coords) as the only argument, either pass each coordinates as up to 4 arguments.

API

getGlobalMat(el:HTMLElement): Matrix

Retrieve the global matrix of the element

setGlobalMatrix(el:HTMLElement, m:Matrix)

Set an element transform matrix so that its global matrix matches m

toLocalMat(el:HTMLElement, m:Matrix): Matrix

Compute the matrix to be assigned to the transform CSS property of el so that its global matrix matches m

getMat(el:HTMLElement): Matrix

Retrieve the current (raw) transform matrix of el (from getComputedStyle)

setMat(el:HTMLElement, m:Matrix)

Set m as the transform CSS property matrix value

transitionMat(m_new:M.Matrix, m_old:M.Matrix):M.Matrix

Compute a transition matrix to translate coordinates from the old space to the new space. See https://en.wikipedia.org/wiki/Change\_of\_basis (here, new and old are swapped because you generally want to express the new coordinate as a function of the old)

The matrices to pass to this function are the global matrice of the elements, that you can get from getGlobalMat()

class CoordTranslator

This class is a helper to translate coordinates from an element to another.

CoordTranslator.T_ab

Transition matrix from b to a why "ab" ? Because : X_a = T_ab X_b where X_a is the position expressed in basis A and X_b is the position expressed in basis B. This way, in the equation, a is near a and b is near b.

CoordTranslator.T_ab

CoordTranslator.T_ab inverted

constructor(m_a:M.Matrix, m_b:M.Matrix)

The constructor accept matrices to be more general. m_a and m_b are global transformation matrices. They repectively represents the basis A and the basis B.

create(el_a:HTMLElement|null|undefined, el_b:HTMLElement|null|undefined): CoordTranslator [static]

Shortcut that simply does :

  return new CoordTranslator(
    el_a ? getGlobalMat(el_a) : M.identity(),
    el_b ? getGlobalMat(el_b) : M.identity()
  )

fromAtoB(x_a:Coords): Coords

From x_a, expressed in basis A, compute the equivalent coordinates in basis B.

fromBtoA(x_b:Coords) :Coords

From x_b, expressed in basis B, compute the equivalent coordinates in basis A.

Advanced pattern

To do a real FLIP animation, you would generally get the current position of the element (gm1 = getGlobalMat(el)), move your element in the DOM to its finale location, and retrieve its (new) current location (m2 = getMat(el)). Then compute the matrix for the original position (m1 = toLocal(el, gm1). Finally, pass to your favorite animation framework m1 and m2 ans the start and final value of your animation.