feat(drag): maintainAspectRatio

Author: kurkle

docs/.vuepress/config.js

@@ -145,6 +145,7 @@ 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

@@ -96,7 +96,29 @@ export function mouseDown(chart, event) {
   addHandler(chart, window.document, 'keydown', keyDown);
 }
 
-export function computeDragRect(chart, mode, beginPointEvent, endPointEvent) {
+function applyAspectRatio(rect, aspectRatio, beginPoint) {
+  let width = rect.right - rect.left;
+  let height = rect.bottom - rect.top;
+  const ratio = width / height;
+
+  if (ratio > aspectRatio) {
+    width = height * aspectRatio;
+    if (beginPoint.x === rect.left) {
+      rect.right = rect.left + width;
+    } else {
+      rect.left = rect.right - width;
+    }
+  } else if (ratio < aspectRatio) {
+    height = width / aspectRatio;
+    if (beginPoint.y === rect.top) {
+      rect.bottom = rect.top + height;
+    } else {
+      rect.top = rect.bottom - height;
+    }
+  }
+}
+
+export function computeDragRect(chart, mode, beginPointEvent, endPointEvent, maintainAspectRatio) {
   const xEnabled = directionEnabled(mode, 'x', chart);
   const yEnabled = directionEnabled(mode, 'y', chart);
   let {top, left, right, bottom, width: chartWidth, height: chartHeight} = chart.chartArea;
@@ -113,14 +135,17 @@ export function computeDragRect(chart, mode, beginPointEvent, endPointEvent) {
     top = Math.max(0, Math.min(beginPoint.y, endPoint.y));
     bottom = Math.min(chart.height, Math.max(beginPoint.y, endPoint.y));
   }
-  const width = right - left;
-  const height = bottom - top;
+  const rect = {top, left, right, bottom};
+
+  if (xEnabled && yEnabled && maintainAspectRatio) {
+    applyAspectRatio(rect, chartWidth / chartHeight, beginPoint);
+  }
+
+  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 +160,8 @@ 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, state.dragStart, 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.spec.js

@@ -253,6 +253,54 @@ describe('zoom', function() {
         expect(scaleY.options.min).toBeCloseTo(1.1);
         expect(scaleY.options.max).toBeCloseTo(1.7);
       });
+
+      it('should respect aspectRatio when mode = xy', function() {
+        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'
+                }
+              }
+            }
+          }
+        });
+
+        scaleX = chart.scales.x;
+        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);
+      });
+
     });
   });