js canvas rounded rectangle code example

Example: javascript canvas rectangle rounded corners

let canvas = document.getElementById('example');
let ctx = canvas.getContext('2d');  
ctx.beginPath();
ctx.roundedRectangle(0, 0, 100, 100, 20);
ctx.stroke();

ctx.beginPath();  
ctx.roundedRectangle(5, 5, 90, 90, 15);
ctx.stroke();

CanvasRenderingContext2D.prototype.roundedRectangle = function(x, y, width, height, rounded) {
  const radiansInCircle = 2 * Math.PI;
  const halfRadians = (2 * Math.PI)/2;
  const quarterRadians = (2 * Math.PI)/4;  
  
  // top left arc
  this.arc(rounded + x, rounded + y, rounded, -quarterRadians, halfRadians, true);
  
  // line from top left to bottom left
  this.lineTo(x, y + height - rounded);

  // bottom left arc  
  this.arc(rounded + x, height - rounded + y, rounded, halfRadians, quarterRadians, true); 
  
  // line from bottom left to bottom right
  this.lineTo(x + width - rounded, y + height);

  // bottom right arc
  this.arc(x + width - rounded, y + height - rounded, rounded, quarterRadians, 0, true);  
  
  // line from bottom right to top right
  this.lineTo(x + width, y + rounded);

  // top right arc
  this.arc(x + width - rounded, y + rounded, rounded, 0, -quarterRadians, true); 
  
  // line from top right to top left
  this.lineTo(x + rounded, y);
}