How to Export Annotations in a React Column Chart

Description

This article shows how to export annotation in React Column Charts.

Solution

To export annotations in a chart, start by converting the annotations into foreignObject elements and appending them to the chart’s SVG. Use getBoundingClientRect() to obtain the size and position of each annotation, then transfer the HTML content of the annotation into the foreignObject. Hide the original annotation and append the foreignObject to the SVG. Next, serialize the SVG to a string, render this serialized SVG string onto a canvas, and finally, convert the canvas content to a PNG image. This process ensures that annotations are accurately exported as part of the chart.

Code-snippet:

The following example shows how to export annotation into image.

function clickHandlerJPEG() {
   let svg: SVGSVGElement | null = document.querySelector('#charts_svg');
   if (svg) {
     let annotationEle = document.getElementById('charts_Annotation_Collections')?.querySelectorAll('[id*="charts_Annotation_"]'); 
     if (annotationEle) {
       for (let i = 0; i < annotationEle.length; i++) {
         let annotation: any = annotationEle[i];
         let foreign = document.createElementNS(
           'http://www.w3.org/2000/svg',
           'foreignObject'
         );
         foreign.setAttribute(
           'width',
           (annotation.getBoundingClientRect().width + 10).toString()
         );
         foreign.setAttribute(
           'height', (annotation.getBoundingClientRect().height + 10).toString()
         );
         foreign.setAttribute('x', annotation['style'].left);
         foreign.setAttribute('y', annotation['style'].top);
         foreign.innerHTML = annotation.innerHTML;
         annotation['style'].display = 'none';
         svg.appendChild(foreign);
       }
     }
     let svgData = new XMLSerializer().serializeToString(svg);
     let canvas = document.createElement('canvas');
     document.body.appendChild(canvas);
     let svgSize = svg.getBoundingClientRect();
     canvas.width = svgSize.width;
     canvas.height = svgSize.height;
     let ctx = canvas.getContext('2d');
     if (ctx) {
       ctx.fillStyle = 'white';
       ctx.fillRect(0, 0, canvas.width, canvas.height);
       let img = document.createElement('img');
       img.setAttribute('src', 'data:image/svg+xml;base64,' + btoa(svgData));
       img.onload = function () {
         ctx.drawImage(img, 0, 0);
         let imagedata = canvas.toDataURL('image/png');
         let anchor = document.createElement('a');
         anchor.download = 'Chart.png';
         anchor.href = imagedata;
         document.body.appendChild(anchor);
         anchor.click();
         canvas.remove();
       };
     }C
   }
 }

The following screenshot illustrates the output of the above code snippet

View Sample in Stackblitz