Code review for two-up, pinch-zoom, trackDragging

components/.gitignore

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+node_modules
+build

components/MultiPanel/index.ts

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+import './styles.css';
+
+export default class MultiPanel extends HTMLElement {
+  constructor () {
+    super();
+  }
+
+  connectedCallback () {
+  }
+}
+
+customElements.define('multi-panel', MultiPanel);

components/MultiPanel/styles.css

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+multi-panel {
+
+}

components/PinchZoom/index.ts

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+import './styles.css';
+import { PointerTracker, Pointer } from '../../utils/PointerTracker';
+
+interface Point {
+  clientX: number;
+  clientY: number;
+}
+
+interface ApplyChangeOpts {
+  panX?: number;
+  panY?: number;
+  scaleDiff?: number;
+  originX?: number;
+  originY?: number;
+}
+
+interface SetTransformOpts {
+  scale?: number;
+  x?: number;
+  y?: number;
+  /**
+   * Fire a 'change' event if values are different to current values
+   */
+  allowChangeEvent?: boolean;
+}
+
+function getDistance (a: Point, b?: Point): number {
+  if (!b) return 0;
+  return Math.sqrt((b.clientX - a.clientX) ** 2 + (b.clientY - a.clientY) ** 2);
+}
+
+function getMidpoint (a: Point, b?: Point): Point {
+  if (!b) return a;
+
+  return {
+    clientX: (a.clientX + b.clientX) / 2,
+    clientY: (a.clientY + b.clientY) / 2
+  };
+}
+
+// I'd rather use DOMMatrix/DOMPoint here, but the browser support isn't good enough.
+// Given that, better to use something everything supports.
+let cachedSvg: SVGSVGElement;
+
+function getSVG (): SVGSVGElement {
+  return cachedSvg || (cachedSvg = document.createElementNS('http://www.w3.org/2000/svg', 'svg'));
+}
+
+function createMatrix (): SVGMatrix {
+  return getSVG().createSVGMatrix();
+}
+
+function createPoint (): SVGPoint {
+  return getSVG().createSVGPoint();
+}
+
+export default class PinchZoom extends HTMLElement {
+  // The element that we'll transform.
+  // Ideally this would be shadow DOM, but we don't have the browser
+  // support yet.
+  private _positioningEl?: Element;
+  // Current transform.
+  private _transform: SVGMatrix = createMatrix();
+
+  constructor () {
+    super();
+
+    // Watch for children changes.
+    // Note this won't fire for initial contents,
+    // so _stageElChange is also called in connectedCallback.
+    new MutationObserver(() => this._stageElChange())
+      .observe(this, { childList: true });
+
+    // Watch for pointers
+    const pointerTracker: PointerTracker = new PointerTracker(this, {
+      start: (pointer, event) => {
+        // We only want to track 2 pointers at most
+        if (pointerTracker.currentPointers.length === 2 || !this._positioningEl) return false;
+        event.preventDefault();
+
+        // Record current state
+        pointerTracker.resetStartPointers();
+        return true;
+      },
+      move: previousPointers => {
+        this._onPointerMove(previousPointers, pointerTracker.currentPointers);
+      }
+    });
+
+    this.addEventListener('wheel', event => this._onWheel(event));
+  }
+
+  connectedCallback () {
+    this._stageElChange();
+  }
+
+  get x () {
+    return this._transform.e;
+  }
+
+  get y () {
+    return this._transform.f;
+  }
+
+  get scale () {
+    return this._transform.a;
+  }
+
+  /**
+   * Update the stage with a given scale/x/y.
+   */
+  setTransform (opts: SetTransformOpts = {}) {
+    const {
+      scale = this.scale,
+      allowChangeEvent = false
+    } = opts;
+
+    let {
+      x = this.x,
+      y = this.y
+    } = opts;
+
+    // If we don't have an element to position, just set the value as given.
+    // We'll check bounds later.
+    if (!this._positioningEl) {
+      this._updateTransform(scale, x, y, allowChangeEvent);
+      return;
+    }
+
+    // Get current layout
+    const thisBounds = this.getBoundingClientRect();
+    const positioningElBounds = this._positioningEl.getBoundingClientRect();
+
+    // Not displayed. May be disconnected or display:none.
+    // Just take the values, and we'll check bounds later.
+    if (!thisBounds.width || !thisBounds.height) {
+      this._updateTransform(scale, x, y, allowChangeEvent);
+      return;
+    }
+
+    // Create points for _positioningEl.
+    let topLeft = createPoint();
+    topLeft.x = positioningElBounds.left - thisBounds.left;
+    topLeft.y = positioningElBounds.top - thisBounds.top;
+    let bottomRight = createPoint();
+    bottomRight.x = positioningElBounds.width + topLeft.x;
+    bottomRight.y = positioningElBounds.height + topLeft.y;
+
+    // Calculate the intended position of _positioningEl.
+    let matrix = createMatrix()
+      .translate(x, y)
+      .scale(scale)
+      // Undo current transform
+      .multiply(this._transform.inverse());
+
+    topLeft = topLeft.matrixTransform(matrix);
+    bottomRight = bottomRight.matrixTransform(matrix);
+
+    // Ensure _positioningEl can't move beyond out-of-bounds.
+    // Correct for x
+    if (topLeft.x > thisBounds.width) {
+      x += thisBounds.width - topLeft.x;
+    } else if (bottomRight.x < 0) {
+      x += -bottomRight.x;
+    }
+
+    // Correct for y
+    if (topLeft.y > thisBounds.height) {
+      y += thisBounds.height - topLeft.y;
+    } else if (bottomRight.y < 0) {
+      y += -bottomRight.y;
+    }
+
+    this._updateTransform(scale, x, y, allowChangeEvent);
+  }
+
+  /**
+   * Update transform values without checking bounds. This is only called in setTransform.
+   */
+  _updateTransform (scale: number, x: number, y: number, allowChangeEvent: boolean) {
+    // Return if there's no change
+    if (
+      scale === this.scale &&
+      x === this.x &&
+      y === this.y
+    ) return;
+
+    this._transform.e = x;
+    this._transform.f = y;
+    this._transform.d = this._transform.a = scale;
+
+    this.style.setProperty('--x', this.x + 'px');
+    this.style.setProperty('--y', this.y + 'px');
+    this.style.setProperty('--scale', this.scale + '');
+
+    if (allowChangeEvent) {
+      const event = new Event('change', { bubbles: true });
+      this.dispatchEvent(event);
+    }
+  }
+
+  /**
+   * Called when the direct children of this element change.
+   * Until we have have shadow dom support across the board, we
+   * require a single element to be the child of <pinch-zoom>, and
+   * that's the element we pan/scale.
+   */
+  private _stageElChange () {
+    this._positioningEl = undefined;
+
+    if (this.children.length === 0) {
+      console.warn('There should be at least one child in <pinch-zoom>.');
+      return;
+    }
+
+    this._positioningEl = this.children[0];
+
+    if (this.children.length > 1) {
+      console.warn('<pinch-zoom> must not have more than one child.');
+    }
+
+    // Do a bounds check
+    this.setTransform();
+  }
+
+  private _onWheel (event: WheelEvent) {
+    event.preventDefault();
+
+    const thisRect = this.getBoundingClientRect();
+    let { deltaY } = event;
+    const { ctrlKey, deltaMode } = event;
+
+    if (deltaMode === 1) { // 1 is "lines", 0 is "pixels"
+      // Firefox uses "lines" for some types of mouse
+      deltaY *= 15;
+    }
+
+    // ctrlKey is true when pinch-zooming on a trackpad.
+    const divisor = ctrlKey ? 100 : 300;
+    const scaleDiff = 1 - deltaY / divisor;
+
+    this._applyChange({
+      scaleDiff,
+      originX: event.clientX - thisRect.left,
+      originY: event.clientY - thisRect.top
+    });
+  }
+
+  private _onPointerMove (previousPointers: Pointer[], currentPointers: Pointer[]) {
+    // Combine next points with previous points
+    const thisRect = this.getBoundingClientRect();
+
+    // For calculating panning movement
+    const prevMidpoint = getMidpoint(previousPointers[0], previousPointers[1]);
+    const newMidpoint = getMidpoint(currentPointers[0], currentPointers[1]);
+
+    // Midpoint within the element
+    const originX = prevMidpoint.clientX - thisRect.left;
+    const originY = prevMidpoint.clientY - thisRect.top;
+
+    // Calculate the desired change in scale
+    const prevDistance = getDistance(previousPointers[0], previousPointers[1]);
+    const newDistance = getDistance(currentPointers[0], currentPointers[1]);
+    const scaleDiff = prevDistance ? newDistance / prevDistance : 1;
+
+    this._applyChange({
+      originX, originY, scaleDiff,
+      panX: newMidpoint.clientX - prevMidpoint.clientX,
+      panY: newMidpoint.clientY - prevMidpoint.clientY
+    });
+  }
+
+  /** Transform the view & fire a change event */
+  private _applyChange (opts: ApplyChangeOpts = {}) {
+    const {
+      panX = 0, panY = 0,
+      originX = 0, originY = 0,
+      scaleDiff = 1
+    } = opts;
+
+    const matrix = createMatrix()
+      // Translate according to panning.
+      .translate(panX, panY)
+      // Scale about the origin.
+      .translate(originX, originY)
+      .scale(scaleDiff)
+      .translate(-originX, -originY)
+      // Apply current transform.
+      .multiply(this._transform);
+
+    // Convert the transform into basic translate & scale.
+    this.setTransform({
+      scale: matrix.a,
+      x: matrix.e,
+      y: matrix.f,
+      allowChangeEvent: true
+    });
+  }
+}
+
+customElements.define('pinch-zoom', PinchZoom);
+
+// TODO:
+// scale by method, which takes a scaleDiff and a center
+// Go to new scale pos, animate to new scale pos
+// On change event
+// scale & x & y props
+// Exclude selector
+// Anchor point for resize

components/PinchZoom/missing-types.d.ts

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+declare interface CSSStyleDeclaration {
+  willChange: string | null;
+}
+
+// TypeScript, you make me sad.
+// https://github.com/Microsoft/TypeScript/issues/18756
+interface Window {
+  PointerEvent: typeof PointerEvent;
+  Touch: typeof Touch;
+}

components/PinchZoom/styles.css

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+pinch-zoom {
+  display: block;
+  overflow: hidden;
+  touch-action: none;
+  --scale: 1;
+  --x: 0;
+  --y: 0;
+}
+
+pinch-zoom > * {
+  transform: translate(var(--x), var(--y)) scale(var(--scale));
+  transform-origin: 0 0;
+  will-change: transform;
+}