3 files changed, 50 insertions, 45 deletions
diff --git a/src/app.js b/src/app.js
index 3afc329..30b4467 100644
--- a/src/app.js
+++ b/src/app.js
@@ -2,14 +2,7 @@ import zoom from './modules/zoom.js';
 import pan from './modules/pan.js';
 
 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'));
-}
+  object = document.querySelector('object');
 
 // 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
@@ -17,15 +10,18 @@ function reset(elements) {
 
 window.addEventListener('load', function () {
   const svg = object.contentDocument.querySelector('svg'),
-    pannableAndZoomableElements = [img, svg];
+    targetEl = svg.querySelector('g'),
+    pointer = svg.querySelector('#pointer'),
+    options = { passive: false };
 
-  button.addEventListener('click', () => {
-    [button, container].forEach(el => el.classList.toggle('switch'));
-    reset(pannableAndZoomableElements);
-  });
+  svg.addEventListener('wheel', e => zoom(targetEl, e, optionalZoomFactor), options);
+  svg.addEventListener('pointerdown', e => pan(svg, targetEl, e), options);
+
+  svg.addEventListener('pointermove', e => {
+    const pt = new DOMPoint(e.clientX, e.clientY),
+      svgP = pt.matrixTransform(targetEl.getScreenCTM().inverse());
 
-  pannableAndZoomableElements.forEach(el => {
-    el.addEventListener('wheel', e => zoom(el, e, optionalZoomFactor), { passive: false });
-    el.addEventListener('pointerdown', e => pan(el, e), { passive: false });
+    pointer.setAttributeNS(null, 'cx', svgP.x);
+    pointer.setAttributeNS(null, 'cy', svgP.y);
   });
 });
diff --git a/src/modules/pan.js b/src/modules/pan.js
index 201c2f1..6f2cacf 100644
--- a/src/modules/pan.js
+++ b/src/modules/pan.js
@@ -2,13 +2,6 @@ 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);
 }
@@ -27,35 +20,45 @@ function getTranslateMatrix(startPt, movePt) {
   return translateMatrix.translate(movePt.x - startPt.x, movePt.y - startPt.y);
 }
 
-export default function (el, e) {
+export default function (svg, el, e) {
   e.preventDefault();
 
   const mtx = getComputedTransformMatrix(el),
-    startPt = new DOMPoint(e.clientX, e.clientY),
-    movePt = new DOMPoint();
+    inverseScreenCTM = el.getScreenCTM().inverse();
 
-  let isPanning = false;
+  let startPt = new DOMPoint(e.clientX, e.clientY),
+    movePt = new DOMPoint(),
+    isPanning = false;
 
   function pointerMove(e) {
-    setToCurrentPointerCoords(movePt, e);
+    movePt.x = e.clientX;
+    movePt.y = e.clientY;
 
     if (!isPanning && minDistanceThresholdIsMet(startPt, movePt)) {
       isPanning = true;
       e.target.setPointerCapture(e.pointerId);
-      setToCurrentPointerCoords(startPt, e);
+
+      startPt.x = e.clientX;
+      startPt.y = e.clientY;
+      startPt = startPt.matrixTransform(inverseScreenCTM);
+
       stopEventPropagationToChildren(el, 'click');
     }
 
     if (isPanning) {
-      el.style.transform = getTranslateMatrix(startPt, movePt).multiply(mtx);
+      movePt.x = e.clientX;
+      movePt.y = e.clientY;
+      movePt = movePt.matrixTransform(inverseScreenCTM);
+
+      el.style.transform = mtx.multiply(getTranslateMatrix(startPt, movePt));
     }
   }
 
-  el.addEventListener('pointermove', pointerMove);
+  svg.addEventListener('pointermove', pointerMove);
 
-  el.addEventListener(
+  svg.addEventListener(
     'pointerup',
-    () => el.removeEventListener('pointermove', pointerMove),
+    () => svg.removeEventListener('pointermove', pointerMove),
     { once: true }
   );
 }
diff --git a/src/modules/zoom.js b/src/modules/zoom.js
index 97a23e1..fc0540b 100644
--- a/src/modules/zoom.js
+++ b/src/modules/zoom.js
@@ -8,35 +8,41 @@ function getScale(e, factor) {
   return zoomIn(e.deltaY) ? 1 + factor : 1 - factor;
 }
 
-function getFocalPointBeforeTransform(el, e) {
-  const { x, y, width, height } = el.getBoundingClientRect();
+function getFocalPointBeforeTransform(el, e, inverseScreenCTM) {
+  const { x, y, width, height } = el.getBoundingClientRect(),
+    pointer = (new DOMPoint(e.clientX, e.clientY)).matrixTransform(inverseScreenCTM),
+    origin = (new DOMPoint(x, y)).matrixTransform(inverseScreenCTM),
+    terminus = (new DOMPoint(x + width, y + height)).matrixTransform(inverseScreenCTM);
 
   return {
-    x: e.clientX,
-    y: e.clientY,
+    x: pointer.x,
+    y: pointer.y,
     relativeToImageSize: {
-      x: (e.clientX - x) / width,
-      y: (e.clientY - y) / height
+      x: (pointer.x - origin.x) / (terminus.x - origin.x),
+      y: (pointer.y - origin.y) / (terminus.y - origin.y)
     }
   };
 }
 
-function getFocalPointAfterTransform(el, fpBeforeTrans) {
+function getFocalPointAfterTransform(el, fpBeforeTrans, inverseScreenCTM) {
   const { x, y, width, height } = el.getBoundingClientRect(),
+    origin = (new DOMPoint(x, y)).matrixTransform(inverseScreenCTM),
+    terminus = (new DOMPoint(x + width, y + height)).matrixTransform(inverseScreenCTM),
     relativeFocalPoint = fpBeforeTrans.relativeToImageSize;
 
   return {
-    x: x + width * relativeFocalPoint.x,
-    y: y + height * relativeFocalPoint.y
+    x: origin.x + (terminus.x - origin.x) * relativeFocalPoint.x,
+    y: origin.y + (terminus.y - origin.y) * relativeFocalPoint.y
   };
 }
 
 function getTranslateMatrix(el, e, scaleMatrix) {
-  const fpBeforeTrans = getFocalPointBeforeTransform(el, e);
+  const inverseScreenCTM = el.getScreenCTM().inverse(),
+    fpBeforeTrans = getFocalPointBeforeTransform(el, e, inverseScreenCTM);
 
   el.style.transform = scaleMatrix;
 
-  const fpAfterTrans = getFocalPointAfterTransform(el, fpBeforeTrans),
+  const fpAfterTrans = getFocalPointAfterTransform(el, fpBeforeTrans, inverseScreenCTM),
     translateMatrix = new DOMMatrix();
 
   return translateMatrix.translate(
@@ -52,5 +58,5 @@ export default function (el, e, factor = 0.1) {
     scale = getScale(e, factor),
     transMtx = getTranslateMatrix(el, e, mtx.scale(scale));
 
-  el.style.transform = transMtx.multiply(mtx).scale(scale);
+  el.style.transform = mtx.multiply(transMtx).scale(scale);
 }