11 files changed, 271 insertions, 193 deletions
diff --git a/README.md b/README.md
index 0ca567d..4d96e8f 100644
--- a/README.md
+++ b/README.md
@@ -1,9 +1,15 @@
-## Install dev server packages
+# Pan-Zoom
 
-    docker run --rm -w /app -v $PWD:/app -u $(id -u):$(id -u) node npm install
+Pan/zoom library for web browsers. Hold and drag an element to pan. Use the mouse wheel to zoom. See `src/app.js` for a usage example.
 
-## Start the dev server
+## To view the demo using Docker
 
-    docker run --rm --init -it -w /app -v $PWD:/app -p 8080:8080 node node dev-server.js
+1. Install the development server packages.
 
-Visit `localhost:8080` to view.
+       docker run --rm -w /app -v $PWD:/app -u $(id -u):$(id -u) node npm install
+
+2. Start the server.
+
+       docker run --rm --init -it -w /app -v $PWD:/app -p 8080:8080 node node dev-server.js
+
+3. Visit `localhost:8080` to view.
diff --git a/package.json b/package.json
index fb86df3..ccfb11c 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,12 @@
 {
-  "name": "svg-pan-zoom",
+  "name": "pan-zoom",
+  "version": "0.1.0",
+  "browser": "index.js",
   "devDependencies": {
     "esbuild": "^0.20.2",
     "esbuild-server": "^0.3.0"
-  }
+  },
+  "files": [
+    "./src/modules"
+  ]
 }
diff --git a/public/assets/css/style.css b/public/assets/css/style.css
new file mode 100644
index 0000000..db47790
--- /dev/null
+++ b/public/assets/css/style.css
@@ -0,0 +1,40 @@
+body {
+  text-align: center;
+  max-width: 100vw;
+}
+
+.container {
+  padding: 0;
+  max-width: 586.033px;
+  max-height: 586.033px;
+  margin: 0 auto;
+  overflow: hidden;
+  border: 1px solid steelblue;
+  background-color: gray;
+}
+
+img, object {
+  touch-action: none;
+}
+
+img {
+  max-width: 100%;
+  border: 1px solid silver;
+  transform: scale(0.9);
+}
+
+.container object, .container.switch img {
+  display: block;
+}
+
+.container img, .container.switch object {
+  display: none;
+}
+
+button .button-text.raster, button.switch .button-text.svg {
+  display: none;
+}
+
+button.switch .button-text.raster {
+  display: inline;
+}
diff --git a/public/assets/images/41156165560-4438592e93-o.webp b/public/assets/images/41156165560-4438592e93-o.webp
new file mode 100644
index 0000000..2ad3fa4
--- /dev/null
+++ b/public/assets/images/41156165560-4438592e93-o.webp
diff --git a/public/assets/images/image.svg b/public/assets/images/image.svg
new file mode 100644
index 0000000..29f9306
--- /dev/null
+++ b/public/assets/images/image.svg
@@ -0,0 +1,108 @@
+<?xml version="1.0" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+  "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<svg viewBox="-200 -150 400 300" version="1.1" xmlns="http://www.w3.org/2000/svg">
+  <style>
+    svg {
+      overflow: hidden;
+      border: 1px solid silver;
+      transform: scale(0.9);
+    }
+
+    circle, rect {
+      fill-opacity: 0.9;
+      filter: drop-shadow(5px 5px 2px rgba(0, 0, 0, .5));
+    }
+  </style>
+  <script type="text/javascript">//<![CDATA[
+    const svgns = 'http://www.w3.org/2000/svg',
+      svg = document.querySelector('svg'),
+      { x: vbX, y: vbY, width: vbWidth, height: vbHeight } = svg.viewBox.baseVal,
+
+      shapeCount = 100,
+      circleRadius = { min: 5, max: 45 },
+      rectSideLength = { min: 5, max: 95 },
+      colorValRange = { min: 0, max: 255 },
+      shadeFactorRange = { min: 0.3, max: 0.7 };
+
+    // source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random#getting_a_random_integer_between_two_values_inclusive
+    function getRandomIntInclusive(min, max) {
+      const minCeiled = Math.ceil(min),
+        maxFloored = Math.floor(max);
+
+      return Math.floor(Math.random() * (maxFloored - minCeiled + 1) + minCeiled);
+    }
+
+    // source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random#getting_a_random_number_between_two_values
+    function getRandomArbitrary(min, max) {
+      return Math.random() * (max - min) + min;
+    }
+
+    function getRandomColorValue() {
+      return getRandomIntInclusive(colorValRange.min, colorValRange.max);
+    }
+
+    function getRandomShadeFactor() {
+      return getRandomArbitrary(shadeFactorRange.min, shadeFactorRange.max);
+    }
+
+    function getRandomOrigin() {
+      return {
+        x: getRandomIntInclusive(vbX, vbX + vbWidth),
+        y: getRandomIntInclusive(vbY, vbY + vbHeight)
+      }
+    }
+
+    function getRandomFillAndStrokeVals() {
+      const fill = ['r', 'g', 'b'].map(() => getRandomColorValue()),
+        stroke = fill.map(v => Math.floor(v * getRandomShadeFactor()));
+
+      return {
+        fill: fill,
+        stroke: stroke
+      };
+    }
+
+    function getRandomCircle(fill, stroke) {
+      const el = document.createElementNS(svgns, 'circle'),
+        r = getRandomIntInclusive(circleRadius.max, circleRadius.min),
+        origin = getRandomOrigin();
+
+      el.setAttributeNS(null, 'cx', origin.x);
+      el.setAttributeNS(null, 'cy', origin.y);
+      el.setAttributeNS(null, 'r', r);
+      el.setAttributeNS(null, 'fill', fill);
+      el.setAttributeNS(null, 'stroke', stroke);
+
+      return el;
+    }
+
+    function getRandomRect(fill, stroke) {
+      const el = document.createElementNS(svgns, 'rect'),
+        [width, height] = ['w', 'h'].map(() =>
+          getRandomIntInclusive(rectSideLength.max, rectSideLength.min)
+        ),
+        origin = getRandomOrigin();
+
+      el.setAttributeNS(null, 'x', origin.x);
+      el.setAttributeNS(null, 'y', origin.y);
+      el.setAttributeNS(null, 'width', width);
+      el.setAttributeNS(null, 'height', height);
+      el.setAttributeNS(null, 'fill', fill);
+      el.setAttributeNS(null, 'stroke', stroke);
+
+      return el;
+    }
+
+    function getRandomShape({ fill: fillVals, stroke: strokeVals }) {
+      const shape = [getRandomCircle, getRandomRect][Math.round(Math.random())],
+        [fill, stroke] = [fillVals, strokeVals].map(v => `rgb(${v.join(', ')})`);
+
+      return shape(fill, stroke);
+    }
+
+    [...Array(shapeCount)]
+      .map(() => getRandomFillAndStrokeVals())
+      .forEach(fillAndStrokeVal => svg.appendChild(getRandomShape(fillAndStrokeVal)));
+  //]]></script>
+</svg>
diff --git a/public/image.svg b/public/image.svg
deleted file mode 100644
index 5a5c3d9..0000000
--- a/public/image.svg
+++ /dev/null
@@ -1,82 +0,0 @@
-<?xml version="1.0" standalone="no"?>
-<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
-  "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
-<svg viewBox="0 0 400 300" version="1.1" xmlns="http://www.w3.org/2000/svg">
-  <style>
-    svg {
-      overflow: hidden;
-    }
-
-    circle, rect {
-      fill-opacity: 0.9;
-    }
-  </style>
-  <script type="text/javascript">//<![CDATA[
-    const svgns = 'http://www.w3.org/2000/svg',
-      svg = document.querySelector('svg'),
-      { width: vbWidth, height: vbHeight } = svg.viewBox.baseVal,
-      shapeCount = 100,
-      maxColorValue = 256,
-      circleRadius = { max: 45, min: 5 },
-      rectSideLength = { max: 95, min: 5 };
-
-    function getRandomInt(max) {
-      return Math.floor(Math.random() * max);
-    }
-
-    function getRandomPositiveInt(max) {
-      return getRandomInt(max) + 1;
-    }
-
-    function getRandomFillAndStrokeVals() {
-      const shadeFactor = Math.random(),
-        fill = ['r', 'g', 'b'].map(() => getRandomInt(maxColorValue)),
-        stroke = fill.map(v => Math.floor(v * shadeFactor));
-
-      return {
-        fill: fill,
-        stroke: stroke
-      };
-    }
-
-    function getRandomCircle(fill, stroke) {
-      const el = document.createElementNS(svgns, 'circle'),
-        r = getRandomPositiveInt(circleRadius.max) + circleRadius.min;
-
-      el.setAttributeNS(null, 'cx', getRandomInt(vbWidth));
-      el.setAttributeNS(null, 'cy', getRandomInt(vbHeight));
-      el.setAttributeNS(null, 'r', r);
-      el.setAttributeNS(null, 'fill', fill);
-      el.setAttributeNS(null, 'stroke', stroke);
-
-      return el;
-    }
-
-    function getRandomRect(fill, stroke) {
-      const el = document.createElementNS(svgns, 'rect'),
-        [width, height] = ['w', 'h'].map(() =>
-          getRandomPositiveInt(rectSideLength.max) + rectSideLength.min
-        );
-
-      el.setAttributeNS(null, 'x', getRandomInt(vbWidth));
-      el.setAttributeNS(null, 'y', getRandomInt(vbHeight));
-      el.setAttributeNS(null, 'width', width);
-      el.setAttributeNS(null, 'height', height);
-      el.setAttributeNS(null, 'fill', fill);
-      el.setAttributeNS(null, 'stroke', stroke);
-
-      return el;
-    }
-
-    function getRandomShape({ fill: fillVals, stroke: strokeVals }) {
-      const shapes = [getRandomCircle, getRandomRect],
-        [fill, stroke] = [fillVals, strokeVals].map(v => `rgb(${v.join(', ')})`);
-
-      return shapes[getRandomInt(shapes.length)](fill, stroke);
-    }
-
-    [...Array(shapeCount)]
-      .map(() => getRandomFillAndStrokeVals())
-      .forEach(fillAndStrokeVal => svg.appendChild(getRandomShape(fillAndStrokeVal)));
-  //]]></script>
-</svg>
diff --git a/public/index.html b/public/index.html
index 8040421..35a3030 100644
--- a/public/index.html
+++ b/public/index.html
@@ -3,31 +3,28 @@
   <head>
     <meta charset="utf-8"/>
     <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
-    <title>SVG Pan & Zoom Example</title>
-    <style>
-      body {
-        text-align: center;
-        max-width: 100vw;
-      }
-
-      object {
-        max-height: 400px;
-        max-width: 100%;
-        background-color: lightsteelblue;
-        border: 1px solid steelblue;
-        touch-action: none;
-      }
-    </style>
+    <title>JavaScript/CSS Pan & Zoom Demo</title>
+    <link rel="stylesheet" href="assets/css/style.css">
   </head>
   <body>
-    <h1>Pan & Zoom an SVG Image with JavaScript</h1>
+    <h1>Pan & Zoom an Element with CSS/JavaScript</h1>
 
     <p>
       Click and drag on the image to pan. Use the mouse wheel
       to zoom in and out.
     </p>
 
-    <object type="image/svg+xml" data="image.svg"></object>
+    <p>
+      <button>
+        <span class="button-text svg">Raster image</span>
+        <span class="button-text raster">SVG image</span>
+      </button>
+    </p>
+
+    <div class="container">
+      <object type="image/svg+xml" data="assets/images/image.svg"></object>
+      <img src="assets/images/41156165560-4438592e93-o.webp"/>
+    </div>
     <script src="app.js"></script>
   </body>
 </html>
diff --git a/src/app.js b/src/app.js
index f5a4fa8..3afc329 100644
--- a/src/app.js
+++ b/src/app.js
@@ -1,18 +1,31 @@
 import zoom from './modules/zoom.js';
 import pan from './modules/pan.js';
 
-window.addEventListener('load', function () {
-  const svg = document.querySelector('object').contentDocument.querySelector('svg');
+const optionalZoomFactor = 0.1,
+  container = document.querySelector('.container'),
+  object = document.querySelector('object'),
+  img = document.querySelector('img'),
+  button = document.querySelector('button');
+
+function reset(elements) {
+  elements.forEach(el => el.removeAttribute('style'));
+}
 
-  svg.addEventListener('wheel', e => {
-    e.preventDefault();
+// If embedding an SVG using an <object> tag, it's necessary to wait until the
+// page has loaded before querying its `contentDocument`, otherwise it will be
+// `null`.
 
-    svg.setAttributeNS(null, 'viewBox', zoom(svg, e));
-  }, { passive: false });
+window.addEventListener('load', function () {
+  const svg = object.contentDocument.querySelector('svg'),
+    pannableAndZoomableElements = [img, svg];
 
-  svg.addEventListener('pointerdown', e => {
-    e.preventDefault();
+  button.addEventListener('click', () => {
+    [button, container].forEach(el => el.classList.toggle('switch'));
+    reset(pannableAndZoomableElements);
+  });
 
-    pan(svg, e);
-  }, { passive: false });
+  pannableAndZoomableElements.forEach(el => {
+    el.addEventListener('wheel', e => zoom(el, e, optionalZoomFactor), { passive: false });
+    el.addEventListener('pointerdown', e => pan(el, e), { passive: false });
+  });
 });
diff --git a/src/modules/pan.js b/src/modules/pan.js
index 9faae0a..201c2f1 100644
--- a/src/modules/pan.js
+++ b/src/modules/pan.js
@@ -1,5 +1,14 @@
+import getComputedTransformMatrix from './utils.js';
+
 const minDistanceThreshold = 5;
 
+function setToCurrentPointerCoords(point, e) {
+  point.x = e.clientX;
+  point.y = e.clientY;
+
+  return point;
+}
+
 function distanceBetween({ x: x1, y: y1 }, { x: x2, y: y2 }) {
   return Math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2);
 }
@@ -8,46 +17,21 @@ function minDistanceThresholdIsMet(startPt, endPt) {
   return distanceBetween(startPt, endPt) >= minDistanceThreshold;
 }
 
-function getPositionChangeInLocalCoords(svg, startPt, endPt) {
-  const matrix = svg.getScreenCTM().inverse(),
-    localStartPt = startPt.matrixTransform(matrix),
-    localEndPt = endPt.matrixTransform(matrix);
-
-  return {
-    x: localStartPt.x - localEndPt.x,
-    y: localStartPt.y - localEndPt.y
-  };
-}
-
-function stopEventPropagationToChildren(svg, type) {
-  svg.addEventListener(type, e => e.stopPropagation(), { capture: true, once: true });
-}
-
-function setToCurrentPointerCoords(point, e) {
-  point.x = e.clientX;
-  point.y = e.clientY;
-
-  return point;
+function stopEventPropagationToChildren(el, type) {
+  el.addEventListener(type, e => e.stopPropagation(), { capture: true, once: true });
 }
 
-function getPanCoords(svg, startPt, movePt, initialPos) {
-  const posChange = getPositionChangeInLocalCoords(svg, startPt, movePt);
+function getTranslateMatrix(startPt, movePt) {
+  const translateMatrix = new DOMMatrix();
 
-  return {
-    x: initialPos.x + posChange.x,
-    y: initialPos.y + posChange.y
-  };
+  return translateMatrix.translate(movePt.x - startPt.x, movePt.y - startPt.y);
 }
 
-function setViewBoxPosition(svg, { x, y }) {
-  const { width, height } = svg.viewBox.baseVal;
-
-  svg.setAttributeNS(null, 'viewBox', `${x} ${y} ${width} ${height}`);
-}
+export default function (el, e) {
+  e.preventDefault();
 
-export default function (svg, e) {
-  const { x, y } = svg.viewBox.baseVal,
-    startPt = setToCurrentPointerCoords(new DOMPoint(), e),
+  const mtx = getComputedTransformMatrix(el),
+    startPt = new DOMPoint(e.clientX, e.clientY),
     movePt = new DOMPoint();
 
   let isPanning = false;
@@ -59,19 +43,19 @@ export default function (svg, e) {
       isPanning = true;
       e.target.setPointerCapture(e.pointerId);
       setToCurrentPointerCoords(startPt, e);
-      stopEventPropagationToChildren(svg, 'click');
+      stopEventPropagationToChildren(el, 'click');
     }
 
     if (isPanning) {
-      setViewBoxPosition(svg, getPanCoords(svg, startPt, movePt, { x, y }));
+      el.style.transform = getTranslateMatrix(startPt, movePt).multiply(mtx);
     }
   }
 
-  svg.addEventListener('pointermove', pointerMove);
+  el.addEventListener('pointermove', pointerMove);
 
-  svg.addEventListener(
+  el.addEventListener(
     'pointerup',
-    () => svg.removeEventListener('pointermove', pointerMove),
+    () => el.removeEventListener('pointermove', pointerMove),
     { once: true }
   );
 }
diff --git a/src/modules/utils.js b/src/modules/utils.js
new file mode 100644
index 0000000..e7f5c55
--- /dev/null
+++ b/src/modules/utils.js
@@ -0,0 +1,8 @@
+const digits = /-?\d+\.?\d*/g;
+
+export default function getComputedTransformMatrix(el) {
+  const matrixSequence = getComputedStyle(el).transform.match(digits),
+    identityMatrix = '';
+
+  return new DOMMatrix(matrixSequence || identityMatrix);
+}
diff --git a/src/modules/zoom.js b/src/modules/zoom.js
index 24ddb79..97a23e1 100644
--- a/src/modules/zoom.js
+++ b/src/modules/zoom.js
@@ -1,57 +1,56 @@
-const zoomStepRatio = 0.25,
-  positive = 1,
-  negative = -1;
-
-function toLocalCoords(svg, x, y) {
-  const clientP = new DOMPoint(x, y);
-
-  return clientP.matrixTransform(svg.getScreenCTM().inverse());
-}
+import getComputedTransformMatrix from './utils.js';
 
 function zoomIn(deltaY) {
   return deltaY < 0;
 }
 
-function calcSizeChangeAmounts(width, height) {
-  return {
-    width: width * zoomStepRatio,
-    height: height * zoomStepRatio
-  };
+function getScale(e, factor) {
+  return zoomIn(e.deltaY) ? 1 + factor : 1 - factor;
 }
 
-function calcValChangeRatios(focusPoint, x, y, width, height) {
+function getFocalPointBeforeTransform(el, e) {
+  const { x, y, width, height } = el.getBoundingClientRect();
+
   return {
-    x: (focusPoint.x - x) / width,
-    y: (focusPoint.y - y) / height,
-    width: (width + x - focusPoint.x) / width,
-    height: (height + y - focusPoint.y) / height
+    x: e.clientX,
+    y: e.clientY,
+    relativeToImageSize: {
+      x: (e.clientX - x) / width,
+      y: (e.clientY - y) / height
+    }
   };
 }
 
-function calcValChangeAmounts(focusPoint, x, y, width, height) {
-  const changeAmount = calcSizeChangeAmounts(width, height),
-    valChangeRatio = calcValChangeRatios(focusPoint, x, y, width, height);
+function getFocalPointAfterTransform(el, fpBeforeTrans) {
+  const { x, y, width, height } = el.getBoundingClientRect(),
+    relativeFocalPoint = fpBeforeTrans.relativeToImageSize;
 
   return {
-    x: valChangeRatio.x * changeAmount.width,
-    y: valChangeRatio.y * changeAmount.height,
-    width: valChangeRatio.width * changeAmount.width,
-    height: valChangeRatio.height * changeAmount.height
+    x: x + width * relativeFocalPoint.x,
+    y: y + height * relativeFocalPoint.y
   };
 }
 
-export default function (svg, e) {
-  const pointerPosition = toLocalCoords(svg, e.clientX, e.clientY),
-    sign = zoomIn(e.deltaY) ? positive : negative,
-    { x, y, width, height } = svg.viewBox.baseVal,
-    changeAmount = calcValChangeAmounts(pointerPosition, x, y, width, height),
+function getTranslateMatrix(el, e, scaleMatrix) {
+  const fpBeforeTrans = getFocalPointBeforeTransform(el, e);
+
+  el.style.transform = scaleMatrix;
+
+  const fpAfterTrans = getFocalPointAfterTransform(el, fpBeforeTrans),
+    translateMatrix = new DOMMatrix();
+
+  return translateMatrix.translate(
+    fpBeforeTrans.x - fpAfterTrans.x,
+    fpBeforeTrans.y - fpAfterTrans.y
+  );
+}
+
+export default function (el, e, factor = 0.1) {
+  e.preventDefault();
 
-    attr = {
-      x: x + sign * changeAmount.x,
-      y: y + sign * changeAmount.y,
-      width: width + sign * (-changeAmount.x - changeAmount.width),
-      height: height + sign * (-changeAmount.y - changeAmount.height)
-    };
+  const mtx = getComputedTransformMatrix(el),
+    scale = getScale(e, factor),
+    transMtx = getTranslateMatrix(el, e, mtx.scale(scale));
 
-  return `${attr.x} ${attr.y} ${attr.width} ${attr.height}`;
+  el.style.transform = transMtx.multiply(mtx).scale(scale);
 }