fix(axis): scale tick labels to fix text truncation on chrome (#38)

emmacunningham · web-flow · commit 99c2332113a7 · 2019-02-06T07:39:46.000-08:00
fixes #18
diff --git a/src/lib/axes/canvas_text_bbox_calculator.ts b/src/lib/axes/canvas_text_bbox_calculator.ts
@@ -5,23 +5,28 @@ export class CanvasTextBBoxCalculator implements BBoxCalculator {
   private attachedRoot: HTMLElement;
   private offscreenCanvas: HTMLCanvasElement;
   private context: CanvasRenderingContext2D | null;
-  // TODO specify styles for text
-  // TODO specify how to hide the svg from the current dom view
-  // like moving it a -9999999px
+  private scaledFontSize: number;
+
   constructor(rootElement?: HTMLElement) {
     this.offscreenCanvas = document.createElement('canvas');
     this.context = this.offscreenCanvas.getContext('2d');
     this.attachedRoot = rootElement || document.documentElement;
     this.attachedRoot.appendChild(this.offscreenCanvas);
+    this.scaledFontSize = 100;
   }
   compute(text: string, fontSize = 16, fontFamily = 'Arial'): Option<BBox> {
     if (!this.context) {
       return none;
     }
-    this.context.font = `${fontSize}px ${fontFamily}`;
+
+    // We scale the text up to get a more accurate computation of the width of the text
+    // because `measureText` can vary a lot between browsers.
+    const scalingFactor = this.scaledFontSize / fontSize;
+    this.context.font = `${this.scaledFontSize}px ${fontFamily}`;
     const measure = this.context.measureText(text);
+
     return some({
-      width: measure.width,
+      width: measure.width / scalingFactor,
       height: fontSize,
     });
   }
diff --git a/src/stories/axis.tsx b/src/stories/axis.tsx
@@ -15,6 +15,7 @@ import {
 } from '..';
 import { PartialTheme } from '../lib/themes/theme';
 import { LineSeries } from '../specs';
+import { DataGenerator } from '../utils/data_generators/data_generator';
 
 function createThemeAction(title: string, min: number, max: number, value: number) {
   return number(title, value, {
@@ -266,4 +267,28 @@ storiesOf('Axis', module)
         />
       </Chart>
     );
+  })
+  .add('w many tick labels', () => {
+    const dg = new DataGenerator();
+    const data = dg.generateSimpleSeries(31);
+    return (
+      <Chart renderer="canvas" className={'story-chart'}>
+        <Settings debug={true} />
+        <Axis
+          id={getAxisId('bottom')}
+          position={Position.Bottom}
+          title={'Bottom axis'}
+          showOverlappingTicks={true}
+        />
+        <AreaSeries
+          id={getSpecId('lines')}
+          xScaleType={ScaleType.Linear}
+          yScaleType={ScaleType.Linear}
+          xAccessor="x"
+          yAccessors={['y']}
+          data={data}
+          yScaleToDataExtent={false}
+        />
+      </Chart>
+    );
   });
