Callout position calculated when label is drawn

docs/.vuepress/config.js

@@ -173,7 +173,13 @@ module.exports = {
             'charts/line',
           ],
         },
-        'interaction',
+        {
+          title: 'Interaction',
+          children: [
+            'interaction/interaction',
+            'interaction/dragging',
+          ],
+        },
         'utils',
       ]
     }

docs/samples/interaction/dragging.md

@@ -0,0 +1,195 @@
+# Dragging annotations
+
+```js chart-editor
+// <block:setup:6>
+Utils.srand(8);
+
+const data = {
+  labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
+  datasets: [{
+    type: 'line',
+    label: 'Dataset 1',
+    borderColor: 'rgb(54, 162, 235)',
+    borderWidth: 2,
+    fill: false,
+    data: Utils.numbers({count: 7, min: 0, max: 100}),
+  }]
+};
+// </block:setup>
+
+// <block:annotation1:1>
+const annotation1 = {
+  type: 'box',
+  backgroundColor: 'rgba(165, 214, 167, 0.2)',
+  borderColor: 'rgb(165, 214, 167)',
+  borderWidth: 2,
+  label: {
+    display: true,
+    content: ['Box annotation', 'to drag'],
+    textAlign: 'center'
+  },
+  xMax: 'May',
+  xMin: 'April',
+  xScaleID: 'x',
+  yMax: 75,
+  yMin: 25,
+  yScaleID: 'y'
+};
+// </block:annotation1>
+
+// <block:annotation2:2>
+const annotation2 = {
+  type: 'label',
+  backgroundColor: 'rgba(255, 99, 132, 0.25)',
+  borderWidth: 3,
+  borderColor: 'black',
+  content: ['Label annotation', 'to drag'],
+  callout: {
+    display: true,
+    borderColor: 'black',
+  },
+  xValue: 1,
+  yValue: 40
+};
+// </block:annotation2>
+
+// <block:annotation3:3>
+const annotation3 = {
+  type: 'point',
+  backgroundColor: 'rgba(0, 255, 255, 0.4)',
+  borderWidth: 2,
+  borderColor: 'black',
+  radius: 20,
+  xValue: 'March',
+  yValue: 50
+};
+// </block:annotation3>
+
+// <block:annotation4:4>
+const annotation4 = {
+  type: 'polygon',
+  backgroundColor: 'rgba(150, 0, 0, 0.25)',
+  borderWidth: 2,
+  borderColor: 'black',
+  radius: 50,
+  sides: 6,
+  xValue: 'June',
+  yValue: 20
+};
+// </block:annotation4>
+
+// <block:utils:7>
+let element;
+let lastEvent;
+
+const drag = function(moveX, moveY) {
+  element.x += moveX;
+  element.y += moveY;
+  element.x2 += moveX;
+  element.y2 += moveY;
+  element.centerX += moveX;
+  element.centerY += moveY;
+  if (element.elements && element.elements.length) {
+    for (const subEl of element.elements) {
+      subEl.x += moveX;
+      subEl.y += moveY;
+      subEl.x2 += moveX;
+      subEl.y2 += moveY;
+      subEl.centerX += moveX;
+      subEl.centerY += moveY;
+      subEl.bX += moveX;
+      subEl.bY += moveY;
+    }
+  }
+};
+
+const handleElementDragging = function(event) {
+  if (!lastEvent || !element) {
+    return;
+  }
+  const moveX = event.x - lastEvent.x;
+  const moveY = event.y - lastEvent.y;
+  drag(moveX, moveY);
+  lastEvent = event;
+  return true;
+};
+
+const handleDrag = function(event) {
+  if (element) {
+    switch (event.type) {
+    case 'mousemove':
+      return handleElementDragging(event);
+    case 'mouseout':
+    case 'mouseup':
+      lastEvent = undefined;
+      break;
+    case 'mousedown':
+      lastEvent = event;
+      break;
+    default:
+    }
+  }
+};
+// </block:dragger>
+
+// <block:dragger:5>
+const dragger = {
+  id: 'dragger',
+  beforeEvent(chart, args, options) {
+    if (handleDrag(args.event)) {
+      args.changed = true;
+      return;
+    }
+  }
+};
+// </block:dragger>
+
+/* <block:config:0> */
+const config = {
+  type: 'line',
+  plugins: [dragger],
+  data,
+  options: {
+    events: ['mousedown', 'mouseup', 'mousemove', 'mouseout'],
+    scales: {
+      y: {
+        beginAtZero: true,
+        min: 0,
+        max: 100
+      }
+    },
+    plugins: {
+      annotation: {
+        enter(ctx) {
+          element = ctx.element;
+        },
+        leave() {
+          element = undefined;
+          lastEvent = undefined;
+        },
+        annotations: {
+          annotation1,
+          annotation2,
+          annotation3,
+          annotation4
+        }
+      }
+    }
+  }
+};
+/* </block:config> */
+
+const actions = [
+  {
+    name: 'Reset dragging',
+    handler: function(chart) {
+      chart.update();
+    }
+  }
+];
+
+module.exports = {
+  actions: actions,
+  config: config,
+};
+```

src/types/label.js

@@ -46,13 +46,11 @@ export default class LabelAnnotation extends Element {
     const padding = toPadding(options.padding);
     const labelSize = measureLabelSize(chart.ctx, options);
     const boxSize = measureRect(point, labelSize, options, padding);
-    const properties = {
+    return {
       pointX: point.x,
       pointY: point.y,
       ...boxSize
     };
-    properties.calloutPosition = options.callout.display && resolveCalloutPosition(properties, options.callout, options.rotation);
-    return properties;
   }
 }
 
@@ -143,11 +141,12 @@ function calculatePosition(start, size, adjust = 0, position) {
 }
 
 function drawCallout(ctx, element) {
-  const {pointX, pointY, calloutPosition, options} = element;
+  const {pointX, pointY, options} = element;
+  const callout = options.callout;
+  const calloutPosition = callout && callout.display && resolveCalloutPosition(element, callout, options.rotation);
   if (!calloutPosition || element.inRange(pointX, pointY)) {
     return;
   }
-  const callout = options.callout;
 
   ctx.save();
   ctx.beginPath();