$ npm install projectrix --save

Dom Projection (noun): The calculation of an element's position, size, and shape on a web page in relation to an element elsewhere in the DOM hierarchy.

         Projection (noun): The set of styles that will make a target element align with a subject. "Animate the target to the projection of the subject onto the target."

Summary

Dom projection has many uses, such as view transitions, FLIP animations, UI walkthroughs, css-oriented puzzle games, and art. However, implementations of this tricky math technique are usually hidden behind apis that prescribe a specific use-case or technology.

Projectrix provides getProjection(), a pure function that returns the styles needed to align a target element to a subject, as well as the styles needed to align it to its original state. Use the projected styles however you want; if animation is your goal, the projection can be spread directly into Anime.js, Motion One, or your preferred animation engine.

Also provided:

• measureSubject(), a pure function that records a subject's position and shape in case the subject and target cannot coexist (e.g. a FLIP animation where the subject is the target's past)
• setInlineStyles(), a convenient function that sets a target to match a projection
• clearInlineStyles(), a function that clears the styles from setInlineStyles

Usage examples

See all demos here: https://tg.projectrix.dev/demos

FLIP target between parents using Motion One

import { getProjection, measureSubject, setInlineStyles, clearInlineStyles } from 'projectrix';
import { animate } from 'motion';

function flip(target: HTMLElement, nextParent: HTMLElement): void {
  const subject = measureSubject(target);

  nextParent.append(target);

  requestAnimationFrame(() => {
    const { toSubject, toTargetOrigin } = getProjection(subject, target);

    // set target to subject's projection
    setInlineStyles(target, toSubject);

    // FLIP back to origin
    const flipAnimation = animate(
      target,
      { ...toTargetOrigin },
      {
        duration: 1,
        easing: 'ease-out',
      },
    );

    // clear inline styles once they're redundant
    flipAnimation.finished.then(() => clearInlineStyles(target, toTargetOrigin));
  });
}

https://github.com/anxpara/projectrix/assets/90604943/ccbe959b-1fe4-43bd-b4fd-8b24cc55b0d4

Animate target directly to subject using Motion One

import { getProjection, type PartialProjection } from 'projectrix';
import { animate, type AnimationControls } from 'motion';

let currentAnim: AnimationControls | undefined;

function animateDirect(subject: HTMLElement, target: HTMLElement): void {
  // stop current animation; motion one will update target's inline
  // styles to mid-animation values
  if (currentAnim?.currentTime && currentAnim.currentTime < 1) {
    currentAnim.stop();
  }

  const toSubject = getProjection(subject, target).toSubject as PartialProjection;
  delete toSubject.borderStyle; // preserve target border style

  currentAnim = animate(
    target,
    { ...toSubject },
    {
      duration: 0.4,
      easing: 'ease-out',
    },
  );
}

https://github.com/anxpara/projectrix/assets/90604943/37132aed-57eb-43ee-8bec-18fcb1a9d0f7

Match target to subject

import { getProjection, setInlineStyles, type PartialProjectionResults } from 'projectrix';

function match(subject: HTMLElement, target: HTMLElement): void {
  const { toSubject } = getProjection(subject, target) as PartialProjectionResults;
  delete toSubject.borderStyle; // preserve target border style
  
  setInlineStyles(target, toSubject);
}

https://github.com/anxpara/projectrix/assets/90604943/36f594b9-303e-4fae-ba5c-84ed3a6b3290

API / Types / Documentation

Projection

export type Projection = {
  width: string;           // 'Wpx'
  height: string;          // 'Hpx'
  borderStyle: string;     // '' | 'none' | 'solid' | 'dashed' | etc.
  borderWidth: string;     // 'Tpx Rpx Bpx Lpx'
  borderRadius: string;    // 'TLpx TRpx BRpx BLpx'
  transformOrigin: string; // 'X% Y% Zpx'

  /**
   * contains exactly one of the following members, depending on the given transformType option:
   * @member transform: string;   // (default) `matrix3d(${matrix3d})`
   * @member matrix3d: string;
   * @member transformMat4: mat4; // row-major array from gl-matrix
   */
  [TransformType: string]: string | mat4 | any; // any is only necessary to allow spreading into anime.js, motion one, etc.
};
export type PartialProjection = Partial<Projection>;

getProjection(), ProjectionOptions, ProjectionResults

export function getProjection(
  subject: HTMLElement | Measurement, // the element or measurement that you plan to align the target to
  target: HTMLElement,                // the element that you plan to modify
  options?: ProjectionOptions,
): ProjectionResults;

export type TransformType = 'transform' | 'matrix3d' | 'transformMat4';
export type BorderSource = 'subject' | 'target' | 'zero';

export type ProjectionOptions = {
  transformType?: TransformType; // (default = 'transform')

  // designates which element's border width, radius, and style to match.
  // projected width and height are auto-adjusted if the target has content-box sizing.
  // zero means 0px border width and radius
  useBorder?: BorderSource; // (default = 'subject')

  log?: boolean; // (default = false)
};

/**
 * when a subject is projected onto a target, you get two Projections. 'toSubject' contains the set of styles that--when applied
 * to the target element--will make the target visually align to the subject. the styles in 'toTargetOrigin' will make
 * the target align to its original state
 */
export type ProjectionResults = {
  toSubject: Projection;
  toTargetOrigin: Projection;
  transformType: TransformType; // the type of transform that both projections contain
  subject: HTMLElement | Measurement;
  target: HTMLElement;
};
export type PartialProjectionResults = {
  toSubject: PartialProjection;
  toTargetOrigin: PartialProjection;
  transformType: TransformType;
  subject: HTMLElement | Measurement;
  target: HTMLElement;
};

measureSubject(), Measurement

/**
 * measures a subject for future projections. useful if the subject and target cannot coexist,
 * such as a flip animation where the subject is the target's past
 */
export function measureSubject(subject: HTMLElement): Measurement;

export type Measurement = {
  acr: ActualClientRect; // from getActualClientRect
  border: BorderMeasurement;
};
export type BorderMeasurement = { /* style, top, right, bottom, left, radius */ };

setInlineStyles(), clearInlineStyles()

/**
 * sets the inline style on the target for each style in the given partial projection.
 * converts any matrix3d or transformMat4 value to a transform style
 */
export function setInlineStyles(target: HTMLElement, partialProjection: PartialProjection): void;

/**
 * clears the inline style on the target for each style in the given partial projection.
 * if no partial projection is given, assumes target's inline styles were set to a full projection.
 * if the projection contains matrix3d or transformMat4, then the transform style is cleared
 */
export function clearInlineStyles(target: HTMLElement, partialProjection?: PartialProjection): void;

Limitations

• Projectrix will not attempt to match, emulate, or mitigate bugs in rendering engines
  • Stackoverflow: -webkit-transform-style: preserve-3d not working
  • some engines don't follow the preserve-3d used value specs, and still use preserve-3d even when combined with certain grouping properties:
    • Chrome v123 / Blink -- contain: strict | content | paint, content-visibility: auto
    • Firefox v124 / Gecko -- will-change: filter
    • Safari v17.4 / Webkit -- will-change: filter | opacity
    • (Properties not yet supported by particular browsers omitted from their respective lists)
• Projectrix is not an animation engine, and will not attempt to mitigate bugs in animation engines
  • https://github.com/motiondivision/motionone/issues/249
  • some engines might animate perspective incorrectly in particular scenarios
• Targeting an element with an "internal" display value, or any value that causes the element to control its own size, will lead to undefined behavior, since the projected width and height will be ignored:
  • display: inline | table | inline-table | table-row | table-column | table-cell | table-row-group | table-column-group | table-header-group | table-footer-group | ruby-base | ruby-text | ruby-base-container | ruby-text-container | run-in
• performance has not yet been profiled
• SVGs are not yet officially supported, but might happen to work in certain scenarios

Contribute

All contributions are greatly appreciated!

• Feedback, feature requests, and help requests can be posted to the Projectrix Discord
• If you find a bug, please file an issue
• Join my Patreon

<3 anxpara