feat(drag): maintainAspectRatio (#861)

* feat(drag): maintainAspectRatio

* fix: some code climate issues

* fix: lint

Author: kurkle

docs/.vuepress/config.js

@@ -146,6 +146,7 @@ module.exports = {
           children: [
             'drag/category',
             'drag/linear',
+            'drag/linear-ratio',
             'drag/log',
             'drag/time',
             'drag/timeseries',

docs/guide/options.md

@@ -80,7 +80,7 @@ const chart = new Chart('id', {
 | [`drawTime`](#draw-time) | `string` | `beforeDatasetsDraw` | When the dragging box is drawn 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
-
+| `maintainAspectRatio` | `boolean` | `undefined` | Maintain aspect ratio of the chart
 
 ## Draw Time
 

docs/samples/drag/linear-ratio.md

@@ -0,0 +1,112 @@
+# Linear Scales + maintainAspectRatio
+
+Zooming is performed by clicking and selecting an area over the chart with the mouse. Pan is activated by keeping `shift` pressed.
+
+```js chart-editor
+// <block:data:1>
+const NUMBER_CFG = {count: 20, min: -100, max: 100};
+const data = {
+  datasets: [{
+    label: 'My First dataset',
+    borderColor: Utils.randomColor(0.4),
+    backgroundColor: Utils.randomColor(0.1),
+    pointBorderColor: Utils.randomColor(0.7),
+    pointBackgroundColor: Utils.randomColor(0.5),
+    pointBorderWidth: 1,
+    data: Utils.points(NUMBER_CFG),
+  }, {
+    label: 'My Second dataset',
+    borderColor: Utils.randomColor(0.4),
+    backgroundColor: Utils.randomColor(0.1),
+    pointBorderColor: Utils.randomColor(0.7),
+    pointBackgroundColor: Utils.randomColor(0.5),
+    pointBorderWidth: 1,
+    data: Utils.points(NUMBER_CFG),
+  }]
+};
+// </block:data>
+
+// <block:scales:2>
+const scaleOpts = {
+  reverse: true,
+  grid: {
+    borderColor: Utils.randomColor(1),
+    color: 'rgba( 0, 0, 0, 0.1)',
+  },
+  title: {
+    display: true,
+    text: (ctx) => ctx.scale.axis + ' axis',
+  }
+};
+const scales = {
+  x: {
+    position: 'top',
+  },
+  y: {
+    position: 'right',
+  },
+};
+Object.keys(scales).forEach(scale => Object.assign(scales[scale], scaleOpts));
+// </block:scales>
+
+// <block:zoom:0>
+const dragColor = Utils.randomColor(0.4);
+const zoomOptions = {
+  pan: {
+    enabled: true,
+    mode: 'xy',
+    modifierKey: 'shift',
+  },
+  zoom: {
+    mode: 'xy',
+    drag: {
+      enabled: true,
+      borderColor: 'rgb(54, 162, 235)',
+      borderWidth: 1,
+      backgroundColor: 'rgba(54, 162, 235, 0.3)',
+      maintainAspectRatio: true,
+    }
+  }
+};
+// </block:zoom>
+
+const zoomStatus = () => zoomOptions.zoom.drag.enabled ? 'enabled' : 'disabled';
+
+// <block:config:1>
+const config = {
+  type: 'scatter',
+  data: data,
+  options: {
+    scales: scales,
+    plugins: {
+      zoom: zoomOptions,
+      title: {
+        display: true,
+        position: 'bottom',
+        text: (ctx) => 'Zoom: ' + zoomStatus()
+      }
+    },
+  }
+};
+// </block:config>
+
+const actions = [
+  {
+    name: 'Toggle zoom',
+    handler(chart) {
+      zoomOptions.zoom.drag.enabled = !zoomOptions.zoom.drag.enabled;
+      chart.update();
+    }
+  }, {
+    name: 'Reset zoom',
+    handler(chart) {
+      chart.resetZoom();
+    }
+  }
+];
+
+module.exports = {
+  actions,
+  config,
+};
+```

src/handlers.js

@@ -96,31 +96,59 @@ export function mouseDown(chart, event) {
   addHandler(chart, window.document, 'keydown', keyDown);
 }
 
-export function computeDragRect(chart, mode, beginPointEvent, endPointEvent) {
+function applyAspectRatio(endPoint, beginPoint, aspectRatio) {
+  let width = endPoint.x - beginPoint.x;
+  let height = endPoint.y - beginPoint.y;
+  const ratio = Math.abs(width / height);
+
+  if (ratio > aspectRatio) {
+    width = Math.sign(width) * Math.abs(height * aspectRatio);
+  } else if (ratio < aspectRatio) {
+    height = Math.sign(height) * Math.abs(width / aspectRatio);
+  }
+
+  endPoint.x = beginPoint.x + width;
+  endPoint.y = beginPoint.y + height;
+}
+
+function applyMinMaxProps(rect, beginPoint, endPoint, {min, max, prop}) {
+  rect[min] = Math.max(0, Math.min(beginPoint[prop], endPoint[prop]));
+  rect[max] = Math.max(beginPoint[prop], endPoint[prop]);
+}
+
+function getReplativePoints(chart, points, maintainAspectRatio) {
+  const beginPoint = getPointPosition(points.dragStart, chart);
+  const endPoint = getPointPosition(points.dragEnd, chart);
+
+  if (maintainAspectRatio) {
+    const aspectRatio = chart.chartArea.width / chart.chartArea.height;
+    applyAspectRatio(endPoint, beginPoint, aspectRatio);
+  }
+
+  return {beginPoint, endPoint};
+}
+
+export function computeDragRect(chart, mode, points, maintainAspectRatio) {
   const xEnabled = directionEnabled(mode, 'x', chart);
   const yEnabled = directionEnabled(mode, 'y', chart);
-  let {top, left, right, bottom, width: chartWidth, height: chartHeight} = chart.chartArea;
+  const {top, left, right, bottom, width: chartWidth, height: chartHeight} = chart.chartArea;
+  const rect = {top, left, right, bottom};
 
-  const beginPoint = getPointPosition(beginPointEvent, chart);
-  const endPoint = getPointPosition(endPointEvent, chart);
+  const {beginPoint, endPoint} = getReplativePoints(chart, points, maintainAspectRatio && xEnabled && yEnabled);
 
   if (xEnabled) {
-    left = Math.max(0, Math.min(beginPoint.x, endPoint.x));
-    right = Math.min(chart.width, Math.max(beginPoint.x, endPoint.x));
+    applyMinMaxProps(rect, beginPoint, endPoint, {min: 'left', max: 'right', prop: 'x'});
   }
 
   if (yEnabled) {
-    top = Math.max(0, Math.min(beginPoint.y, endPoint.y));
-    bottom = Math.min(chart.height, Math.max(beginPoint.y, endPoint.y));
+    applyMinMaxProps(rect, beginPoint, endPoint, {min: 'top', max: 'bottom', prop: 'y'});
   }
-  const width = right - left;
-  const height = bottom - top;
+
+  const width = rect.right - rect.left;
+  const height = rect.bottom - rect.top;
 
   return {
-    left,
-    top,
-    right,
-    bottom,
+    ...rect,
     width,
     height,
     zoomX: xEnabled && width ? 1 + ((chartWidth - width) / chartWidth) : 1,
@@ -135,8 +163,8 @@ export function mouseUp(chart, event) {
   }
 
   removeHandler(chart, 'mousemove');
-  const {mode, onZoomComplete, drag: {threshold = 0}} = state.options.zoom;
-  const rect = computeDragRect(chart, mode, state.dragStart, event);
+  const {mode, onZoomComplete, drag: {threshold = 0, maintainAspectRatio}} = state.options.zoom;
+  const rect = computeDragRect(chart, mode, {dragStart: state.dragStart, dragEnd: event}, maintainAspectRatio);
   const distanceX = directionEnabled(mode, 'x', chart) ? rect.width : 0;
   const distanceY = directionEnabled(mode, 'y', chart) ? rect.height : 0;
   const distance = Math.sqrt(distanceX * distanceX + distanceY * distanceY);

src/plugin.js

@@ -13,7 +13,7 @@ function draw(chart, caller, options) {
   if (dragOptions.drawTime !== caller || !dragEnd) {
     return;
   }
-  const {left, top, width, height} = computeDragRect(chart, options.zoom.mode, dragStart, dragEnd);
+  const {left, top, width, height} = computeDragRect(chart, options.zoom.mode, {dragStart, dragEnd}, dragOptions.maintainAspectRatio);
   const ctx = chart.ctx;
 
   ctx.save();

test/specs/zoom.wheel.spec.js

@@ -309,6 +309,53 @@ describe('zoom with wheel', function() {
     });
   });
 
+  it('should respect aspectRatio when mode = xy', function() {
+    const chart = window.acquireChart({
+      type: 'line',
+      data,
+      options: {
+        scales: {
+          x: {
+            type: 'linear'
+          },
+          y: {
+            type: 'linear'
+          }
+        },
+        plugins: {
+          legend: false,
+          title: false,
+          zoom: {
+            zoom: {
+              drag: {
+                enabled: true,
+                maintainAspectRatio: true,
+              },
+              mode: 'xy'
+            }
+          }
+        }
+      }
+    });
+
+    const scaleX = chart.scales.x;
+    const scaleY = chart.scales.y;
+
+    jasmine.triggerMouseEvent(chart, 'mousedown', {
+      x: scaleX.getPixelForValue(1.5),
+      y: scaleY.getPixelForValue(1.1)
+    });
+    jasmine.triggerMouseEvent(chart, 'mouseup', {
+      x: scaleX.getPixelForValue(2.8),
+      y: scaleY.getPixelForValue(1.7)
+    });
+
+    expect(scaleX.options.min).toBeCloseTo(1.5);
+    expect(scaleX.options.max).toBeCloseTo(2.1);
+    expect(scaleY.options.min).toBeCloseTo(1.1);
+    expect(scaleY.options.max).toBeCloseTo(1.7);
+  });
+
   describe('events', function() {
     it('should call onZoomStart', function() {
       const startSpy = jasmine.createSpy('started');