3 files changed, 78 insertions, 46 deletions
diff --git a/index.js b/index.js
index b619e1b..c0afa1b 100644
--- a/index.js
+++ b/index.js
@@ -1,2 +1,2 @@
-export { default as pan } from './src/modules/pan.js';
+export { default as pan, programmaticPan } from './src/modules/pan.js';
 export { default as zoom } from './src/modules/zoom.js';
diff --git a/src/modules/pan.js b/src/modules/pan.js
index 6f2cacf..4e6485c 100644
--- a/src/modules/pan.js
+++ b/src/modules/pan.js
@@ -2,11 +2,15 @@ import getComputedTransformMatrix from './utils.js';
 
 const minDistanceThreshold = 5;
 
+function mainButtonPressed(e) {
+  return e.button === 0;
+}
+
 function distanceBetween({ x: x1, y: y1 }, { x: x2, y: y2 }) {
   return Math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2);
 }
 
-function minDistanceThresholdIsMet(startPt, endPt) {
+function exceedsMinDistanceThreshhold(startPt, endPt) {
   return distanceBetween(startPt, endPt) >= minDistanceThreshold;
 }
 
@@ -20,45 +24,68 @@ function getTranslateMatrix(startPt, movePt) {
   return translateMatrix.translate(movePt.x - startPt.x, movePt.y - startPt.y);
 }
 
-export default function (svg, el, e) {
-  e.preventDefault();
+function getTransformMatrices(el) {
+  return {
+    computed: getComputedTransformMatrix(el),
+    inverseScreen: el.getScreenCTM().inverse()
+  };
+}
 
-  const mtx = getComputedTransformMatrix(el),
-    inverseScreenCTM = el.getScreenCTM().inverse();
+function clientToSvgPt({ clientX, clientY }, { inverseScreen }, pt = new DOMPoint()) {
+  pt.x = clientX;
+  pt.y = clientY;
+  return pt.matrixTransform(inverseScreen);
+}
 
-  let startPt = new DOMPoint(e.clientX, e.clientY),
-    movePt = new DOMPoint(),
-    isPanning = false;
+function setPanTransform(el, { computed }, startPt, endPt) {
+  el.style.transform = computed.multiply(getTranslateMatrix(startPt, endPt));
+}
+
+export function programmaticPan(el, from, to) {
+  const matrices = getTransformMatrices(el);
+  const startPt = clientToSvgPt(from, matrices);
+  const endPt = clientToSvgPt(to, matrices);
+
+  el.style.transition = 'transform 0.5s';
+  setPanTransform(el, matrices, startPt, endPt);
+  el.addEventListener('transitionend', () => el.style.transition = '', { once: true });
+}
+
+export default function (el) {
+  let matrices, startPt, movePt, isPanning;
 
   function pointerMove(e) {
     movePt.x = e.clientX;
     movePt.y = e.clientY;
 
-    if (!isPanning && minDistanceThresholdIsMet(startPt, movePt)) {
+    if (!isPanning && exceedsMinDistanceThreshhold(startPt, movePt)) {
       isPanning = true;
-      e.target.setPointerCapture(e.pointerId);
-
-      startPt.x = e.clientX;
-      startPt.y = e.clientY;
-      startPt = startPt.matrixTransform(inverseScreenCTM);
-
+      startPt = clientToSvgPt(e, matrices, startPt);
       stopEventPropagationToChildren(el, 'click');
     }
 
     if (isPanning) {
-      movePt.x = e.clientX;
-      movePt.y = e.clientY;
-      movePt = movePt.matrixTransform(inverseScreenCTM);
-
-      el.style.transform = mtx.multiply(getTranslateMatrix(startPt, movePt));
+      movePt = clientToSvgPt(e, matrices, movePt);
+      setPanTransform(el, matrices, startPt, movePt);
     }
   }
 
-  svg.addEventListener('pointermove', pointerMove);
+  return function(e) {
+    if (!mainButtonPressed(e)) return;
+    e.preventDefault();
+    e.target.setPointerCapture(e.pointerId);
 
-  svg.addEventListener(
-    'pointerup',
-    () => svg.removeEventListener('pointermove', pointerMove),
-    { once: true }
-  );
+    isPanning = false;
+    matrices = getTransformMatrices(el);
+    startPt = new DOMPoint(e.clientX, e.clientY);
+    movePt = new DOMPoint();
+
+    this.addEventListener('pointermove', pointerMove);
+
+    this.addEventListener(
+      'pointerup',
+      () => this.removeEventListener('pointermove', pointerMove),
+      { once: true }
+    );
+  }
 }
diff --git a/src/modules/zoom.js b/src/modules/zoom.js
index fc0540b..834602b 100644
--- a/src/modules/zoom.js
+++ b/src/modules/zoom.js
@@ -5,14 +5,17 @@ function zoomIn(deltaY) {
 }
 
 function getScale(e, factor) {
-  return zoomIn(e.deltaY) ? 1 + factor : 1 - factor;
+  const outMult = 1 - factor;
+  const inMult = 1 + factor / outMult
+
+  return zoomIn(e.deltaY) ? inMult : outMult;
 }
 
 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);
+  const { x, y, width, height } = el.getBoundingClientRect();
+  const pointer = (new DOMPoint(e.clientX, e.clientY)).matrixTransform(inverseScreenCTM);
+  const origin = (new DOMPoint(x, y)).matrixTransform(inverseScreenCTM);
+  const terminus = (new DOMPoint(x + width, y + height)).matrixTransform(inverseScreenCTM);
 
   return {
     x: pointer.x,
@@ -25,10 +28,10 @@ function getFocalPointBeforeTransform(el, e, inverseScreenCTM) {
 }
 
 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;
+  const { x, y, width, height } = el.getBoundingClientRect();
+  const origin = (new DOMPoint(x, y)).matrixTransform(inverseScreenCTM);
+  const terminus = (new DOMPoint(x + width, y + height)).matrixTransform(inverseScreenCTM);
+  const relativeFocalPoint = fpBeforeTrans.relativeToImageSize;
 
   return {
     x: origin.x + (terminus.x - origin.x) * relativeFocalPoint.x,
@@ -37,13 +40,13 @@ function getFocalPointAfterTransform(el, fpBeforeTrans, inverseScreenCTM) {
 }
 
 function getTranslateMatrix(el, e, scaleMatrix) {
-  const inverseScreenCTM = el.getScreenCTM().inverse(),
-    fpBeforeTrans = getFocalPointBeforeTransform(el, e, inverseScreenCTM);
+  const inverseScreenCTM = el.getScreenCTM().inverse();
+  const fpBeforeTrans = getFocalPointBeforeTransform(el, e, inverseScreenCTM);
 
   el.style.transform = scaleMatrix;
 
-  const fpAfterTrans = getFocalPointAfterTransform(el, fpBeforeTrans, inverseScreenCTM),
-    translateMatrix = new DOMMatrix();
+  const fpAfterTrans = getFocalPointAfterTransform(el, fpBeforeTrans, inverseScreenCTM);
+  const translateMatrix = new DOMMatrix();
 
   return translateMatrix.translate(
     fpBeforeTrans.x - fpAfterTrans.x,
@@ -51,12 +54,14 @@ function getTranslateMatrix(el, e, scaleMatrix) {
   );
 }
 
-export default function (el, e, factor = 0.1) {
-  e.preventDefault();
+export default function (el, factor = 0.1) {
+  return e => {
+    e.preventDefault();
 
-  const mtx = getComputedTransformMatrix(el),
-    scale = getScale(e, factor),
-    transMtx = getTranslateMatrix(el, e, mtx.scale(scale));
+    const mtx = getComputedTransformMatrix(el);
+    const scale = getScale(e, factor);
+    const transMtx = getTranslateMatrix(el, e, mtx.scale(scale));
 
-  el.style.transform = mtx.multiply(transMtx).scale(scale);
+    el.style.transform = mtx.multiply(transMtx).scale(scale);
+  }
 }