Snippet Zone

Catmull Rom to Bezier SVG

```
// from: 
```

//   https://github.com/DmitryBaranovskiy/raphael/blob/b5fdbdc9850827eb49622cd0bc81b26025f8128a/dev/raphael.core.js#L1019

```
// and: 
```

//   http://schepers.cc/getting-to-the-point

```
 
```

function catmullRom2bezier(crp, close) {

```
  const d = [];
```

  for (let i = 0, iLen = crp.length; iLen - 2 * !close > i; i += 2) {

```
    const p = [
```
```
      { x: crp[i - 2], y: crp[i - 1] },
```
```
      { x: crp[i], y: crp[i + 1] },
```
```
      { x: crp[i + 2], y: crp[i + 3] },
```
```
      { x: crp[i + 4], y: crp[i + 5] }
```
```
    ];
```
```
    if (close) {
```
```
      if (!i) {
```

        p[0] = { x: crp[iLen - 2], y: crp[iLen - 1] };

```
      } else if (iLen - 4 == i) {
```

        p[3] = { x: crp[0], y: crp[1] };

```
      } else if (iLen - 2 == i) {
```

        p[2] = { x: crp[0], y: crp[1] };

        p[3] = { x: crp[2], y: crp[3] };

```
      }
```
```
    } else {
```
```
      if (iLen - 4 == i) {
```
```
        p[3] = p[2];
```
```
      } else if (!i) {
```

        p[0] = { x: crp[i], y: crp[i + 1] };

```
      }
```
```
    }
```
```
    d.push([
```
```
      'C',
```

      (-p[0].x + 6 * p[1].x + p[2].x) / 6,

      (-p[0].y + 6 * p[1].y + p[2].y) / 6,

      (p[1].x + 6 * p[2].x - p[3].x) / 6,

      (p[1].y + 6 * p[2].y - p[3].y) / 6,

```
      p[2].x,
```
```
      p[2].y
```
```
    ]);
```
```
  }
```
```
 
```
```
  // really for demo purposes:
```
```
 
```

  // draw a tiny rect if less than 2 points

```
  console.log(d.length);
```
```
  if (d.length < 2) {
```
```
    const x = crp[0];
```
```
    const y = crp[1];
```

    return `M ${x} ${y} h 1 v 1 h -1 v-1`;

```
 
```
```
    // draw a line if 2 points
```
```
  } else if (d.length === 2) {
```

    return `M ${crp[0]} ${crp[1]} L ` + crp.flat().join` `;

```
  }
```

  // draw curves if 3 or more (raphael only ever did this, other numbers of points

```
  // were considered invalid)
```

  return  `M ${crp[0]} ${crp[1]}` + d.flat().join` `;

```
}
```
```
 
```
```
// try it out:
```
```
 
```

const pathCommands = catmullRom2bezier([

  100, 100, 200, 100, 200, 300, 170, 150, 120, 180, 120, 120

```
  ], true)
```
```
 
```
```
const svg = `
```
```
  click 3 or more times anywhere<br>
```
```
  <button>clear</button>
```
```
  <svg>
```

    <path d="M 100 100 ${pathCommands}" stroke="blue" fill="none" />

```
  </svg>
```
```
  <style>
```
```
  svg {
```
```
    position:absolute;
```
```
    left:0;top:0;
```
```
    overflow:visible;
```
```
    pointer-events:none;
```
```
  }
```
```
  </style>
```
```
`;
```
```
 
```
```
const div = document.body.appendChild(
```
```
  document.createElement('div')
```
```
);
```
```
div.innerHTML = svg;
```
```
const path = div.querySelector('path')
```
```
 
```
```
let pnts = [];
```
```
 
```
```
function isButton(e) {
```
```
  if (e.target.tagName === 'BUTTON') {
```
```
    pnts = []
```

    path.setAttribute('d', 'M 0 0L0 0');

```
    return true;
```
```
  }
```
```
}
```
```
 
```

document.addEventListener('click', e => {

```
  if (isButton(e)) return;
```
```
  pnts.push(e.clientX, e.clientY);
```

  path.setAttribute('d', catmullRom2bezier(pnts, true))

```
});
```
```
 
```

document.addEventListener('touchend', e => {

```
  if (isButton(e)) return;
```

  pnts.push(e.touchs[0].clientX, e.touchs[0].e.clientY);

  path.setAttribute('d', catmullRom2bezier(pnts, true))

```
});
```

Raphaël was my first deep dive into SVG. Back then, only VML was supported in older IE versions, so using Raphaël was key for tons of commercial work I did (Raphaël generated VML as well as SVG). This snippet is the Catmull Rom code from Raphaël. I’m pretty sure I didn’t know what a Catmull Rom spline was until I found out that using `R` in a path wasn’t supported natively in SVG… and was actually some magic thing that existed in Raphaël alone.

October 1, 2021

// curves // javascript // math // svg

Catmull Rom to Bezier SVG

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