Add drawTime option to zoom drag configuration

docs/guide/options.md

@@ -77,9 +77,22 @@ const chart = new Chart('id', {
 | `backgroundColor` | `Color` | `'rgba(225,225,225,0.3)'` | Fill color
 | `borderColor` | `Color` | `'rgba(225,225,225)'` | Stroke color
 | `borderWidth` | `number` | `0` | Stroke width
+| [`drawTime`](#draw-time) | `string` | `beforeDatasetsDraw` | When the dragging box is dran on the chart
 | `threshold` | `number` | `0` | Minimal zoom distance required before actually applying zoom
 | `modifierKey` | `'ctrl'`\|`'alt'`\|`'shift'`\|`'meta'` | `null` |  Modifier key required for drag-to-zoom
 
+
+## Draw Time
+
+The `drawTime` option for zooming determines where in the chart lifecycle the drag box drawing occurs. Four potential options are available:
+
+| Option | Notes
+| ---- | ----
+| `'beforeDraw'` | Occurs before any drawing takes place
+| `'beforeDatasetsDraw'` | Occurs after drawing of axes, but before datasets
+| `'afterDatasetsDraw'` | Occurs after drawing of datasets but before items such as the tooltip
+| `'afterDraw'` | After other drawing is completed
+
 #### Pinch options
 
 | Name | Type | Default | Description

package.json

@@ -15,6 +15,7 @@
   "scripts": {
     "build": "rollup -c",
     "dev": "karma start --auto-watch --no-single-run --browsers chrome",
+    "dev:ff": "karma start --auto-watch --no-single-run --browsers firefox",
     "docs": "npm run build && vuepress build docs --no-cache",
     "docs:dev": "npm run build && vuepress dev docs --no-cache",
     "lint-js": "eslint \"samples/**/*.html\" \"test/**/*.js\" \"src/**/*.js\"",

src/plugin.js

@@ -6,6 +6,29 @@ import {panFunctions, zoomFunctions, zoomRectFunctions} from './scale.types';
 import {getState, removeState} from './state';
 import {version} from '../package.json';
 
+function draw(chart, caller, options) {
+  const dragOptions = options.zoom.drag;
+  const {dragStart, dragEnd} = getState(chart);
+
+  if (dragOptions.drawTime !== caller || !dragEnd) {
+    return;
+  }
+  const {left, top, width, height} = computeDragRect(chart, options.zoom.mode, dragStart, dragEnd);
+  const ctx = chart.ctx;
+
+  ctx.save();
+  ctx.beginPath();
+  ctx.fillStyle = dragOptions.backgroundColor || 'rgba(225,225,225,0.3)';
+  ctx.fillRect(left, top, width, height);
+
+  if (dragOptions.borderWidth > 0) {
+    ctx.lineWidth = dragOptions.borderWidth;
+    ctx.strokeStyle = dragOptions.borderColor || 'rgba(225,225,225)';
+    ctx.strokeRect(left, top, width, height);
+  }
+  ctx.restore();
+}
+
 export default {
   id: 'zoom',
 
@@ -26,6 +49,7 @@ export default {
       },
       drag: {
         enabled: false,
+        drawTime: 'beforeDatasetsDraw',
         modifierKey: null
       },
       pinch: {
@@ -75,27 +99,20 @@ export default {
     addListeners(chart, options);
   },
 
-  beforeDatasetsDraw: function(chart, args, options) {
-    const {dragStart, dragEnd} = getState(chart);
-
-    if (dragEnd) {
-      const {left, top, width, height} = computeDragRect(chart, options.zoom.mode, dragStart, dragEnd);
+  beforeDatasetsDraw(chart, _args, options) {
+    draw(chart, 'beforeDatasetsDraw', options);
+  },
 
-      const dragOptions = options.zoom.drag;
-      const ctx = chart.ctx;
+  afterDatasetsDraw(chart, _args, options) {
+    draw(chart, 'afterDatasetsDraw', options);
+  },
 
-      ctx.save();
-      ctx.beginPath();
-      ctx.fillStyle = dragOptions.backgroundColor || 'rgba(225,225,225,0.3)';
-      ctx.fillRect(left, top, width, height);
+  beforeDraw(chart, _args, options) {
+    draw(chart, 'beforeDraw', options);
+  },
 
-      if (dragOptions.borderWidth > 0) {
-        ctx.lineWidth = dragOptions.borderWidth;
-        ctx.strokeStyle = dragOptions.borderColor || 'rgba(225,225,225)';
-        ctx.strokeRect(left, top, width, height);
-      }
-      ctx.restore();
-    }
+  afterDraw(chart, _args, options) {
+    draw(chart, 'afterDraw', options);
   },
 
   stop: function(chart) {

test/fixtures/zoom/dragDrawTime.js

@@ -0,0 +1,55 @@
+const data = [];
+for (let i = 0; i < 100; i++) {
+  data.push({x: i, y: Math.sin(i / 25 * Math.PI) * 10});
+}
+
+module.exports = {
+  tolerance: 0.004,
+  config: {
+    type: 'line',
+    data: {
+      datasets: [{
+        data,
+        borderColor: 'red'
+      }]
+    },
+    options: {
+      scales: {
+        x: {type: 'linear', display: false},
+        y: {display: false}
+      },
+      plugins: {
+        legend: false,
+        zoom: {
+          zoom: {
+            drag: {
+              enabled: true,
+              backgroundColor: 'yellow',
+              borderColor: 'black',
+              borderWidth: 1,
+              drawTime: 'afterDraw'
+            },
+          }
+        }
+      },
+      layout: {
+        padding: 2
+      }
+    }
+  },
+  options: {
+    run(chart) {
+      const scaleX = chart.scales.x;
+      const scaleY = chart.scales.y;
+      jasmine.triggerMouseEvent(chart, 'mousedown', {
+        x: scaleX.getPixelForValue(5),
+        y: scaleY.getPixelForValue(10)
+      });
+      jasmine.triggerMouseEvent(chart, 'mousemove', {
+        x: scaleX.getPixelForValue(60),
+        y: scaleY.getPixelForValue(0)
+      });
+      chart.render = function() { };
+    }
+  }
+};

test/specs/defaults.spec.js

@@ -14,6 +14,7 @@ describe('defaults', function() {
       },
       drag: {
         enabled: false,
+        drawTime: 'beforeDatasetsDraw',
         modifierKey: null
       },
       pinch: {

types/options.d.ts

@@ -3,6 +3,7 @@ import { Chart, Color, Point } from 'chart.js';
 
 type Mode = 'x' | 'y' | 'xy';
 type Key = 'ctrl' | 'alt' | 'shift' | 'meta';
+type DrawTime = 'afterDraw' | 'afterDatasetsDraw' | 'beforeDraw' | 'beforeDatasetsDraw';
 
 export interface WheelOptions {
   /**
@@ -52,6 +53,11 @@ export interface DragOptions {
    * Modifier key required for drag-to-zoom
    */
   modifierKey?: Key;
+
+  /**
+   * Draw time required for drag-to-zoom
+   */
+  drawTime?: DrawTime;
 }
 
 export interface PinchOptions {