Tutorial: How to make a circular progress bar widget with React and SVG.
Tags: react, svg, design, tutorial
Published: 2020-02-13 13:33:32

Today I decide to make something special. I was chilling on my bed looking some beautiful UI concept art on Instagram when I got interested in circular progress bars. So I decide to make a simple progress bar made with react and SVG.

You may not know but SVG can be edited with React since the beginning but is not so much used for complex widgets. SVG can be an excellent tool to make powerful tools where quality and performance are needed.

## Some theory first or some calculus

Let's make an arc that represents the percentage value of the progress, it means that we need to evaluate the radiant coordinates of each point interest to design the arc on each percentage value. So let us represent each value as:

```
radius1, radius2 //inner and outer radius of the arc
omegaStart //angulus of the beginning of the arc (0%)
omegaEnd //angulus of the ending of the arc (100%)
omegaValue //angulus of the value (X%)
centerX, centerY //coordinates of the centre of the widget
xStart1, yStart1, xStart2, yStart2 //coordinates of the beginning of the arc (0%)
xEnd1, yEnd1, xEnd2, yEnd2 //coordinates of the ending of the arc (100%)
xValue1, yValue1, xValue2, yValue2  //coordinates of the value (X%)
```

In a blueprint we should see them like this:

![Blueprint](https://i.imgur.com/GZ4LTDK.png)

So each formula should be:

```
omegaValue = omegaStart + (omageEnd-OmegaStart)*X
Coordinate[X,Y] = radius[cos(omega), sin(omega)]
```

## The React Element (with hooks)

```jsx
const ArcProgressBar = ({value, width, omega}) => {

     const omegaRadStart = -omega*Math.PI/180;
     const omegaRadEnd = Math.PI*(1+omega/180);
     console.log(omegaRadStart, omegaRadEnd)
     const radius = 40;
     const innerRadius = (width*40);
     const coonerRadius = (radius-innerRadius)/2;
     const omegaRadValue = omegaRadStart + (omegaRadEnd-omegaRadStart)*value;
     const xyPoint = (r, angle) => [Math.cos(angle), Math.sin(angle)].map(x => 50-(x*r))
     const [x1Start, y1Start] = xyPoint(radius, omegaRadStart);
     const [x2Start, y2Start] = xyPoint(innerRadius, omegaRadStart);
     const [x1End, y1End] = xyPoint(radius, omegaRadEnd);
     const [x2End, y2End] = xyPoint(innerRadius, omegaRadEnd);
     const [x1Value, y1Value] = xyPoint(radius, omegaRadValue);
     const [x2Value, y2Value] = xyPoint(innerRadius, omegaRadValue);

     return (
          <svg viewport="0 0 100 100">
           <path 
            d={`
             M ${x1Start} ${y1Start} 
             A ${radius} ${radius} 0 1 1 ${x1End} ${y1End}  
             A ${coonerRadius} ${coonerRadius} 0 1 1 ${x2End} ${y2End} 
             A ${innerRadius} ${innerRadius} 0 1 0 ${x2Start} ${y2Start} 
             A ${coonerRadius} ${coonerRadius} 0 0 1 ${x1Start} ${y1Start}
             Z`}
            fill="black"
           />
           <path 
            d={`
             M ${x1Start} ${y1Start} 
             A ${radius} ${radius} 0 0 1 ${x1Value} ${y1Value}  
             A ${coonerRadius} ${coonerRadius} 0 1 1 ${x2Value} ${y2Value} 
             A ${innerRadius} ${innerRadius} 0 0 0 ${x2Start} ${y2Start} 
             A ${coonerRadius} ${coonerRadius} 0 1 1 ${x1Start} ${y1Start}
             Z`}
            fill="blue"
           />
          </svg>
     );


};
```

Check it:

{% codepen https://codepen.io/alexgomez88/pen/mdJevZK %}