CanvasRenderingContext2D.lineCap

The CanvasRenderingContext2D.lineCap property of the Canvas 2D API determines how the end points of every line are drawn. There are three possible values for this property and those are: butt, round and square. By default this property is set to butt.

See also the chapter Applying styles and color in the Canvas Tutorial.

Syntax

ctx.lineCap = "butt";
ctx.lineCap = "round";
ctx.lineCap = "square";

Options

butt

The ends of lines are squared off at the endpoints.

round

The ends of lines are rounded.

square

The ends of lines are squared off by adding a box with an equal width and half the height of the line's thickness.

Examples

Using the lineCap property

This is just a simple code snippet using the lineCap property to draw lines with a rounded end.

HTML

<canvas id="canvas"></canvas>

JavaScript

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

ctx.beginPath();
ctx.moveTo(0,0);
ctx.lineWidth = 15;
ctx.lineCap = "round";
ctx.lineTo(100, 100);
ctx.stroke();

Edit the code below and see your changes update live in the canvas:

<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
ctx.beginPath();
ctx.moveTo(0,0);
ctx.lineWidth = 15;
ctx.lineCap = "round";
ctx.lineTo(100, 100);
ctx.stroke();</textarea>

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);

A lineCap example

In this example three lines are drawn, each with a different value for the lineCap property. Two guides to see the exact differences between the three are added. Each of these lines starts and ends exactly on these guides.

The line on the left uses the default butt option. It's drawn completely flush with the guides. The second is set to use the round option. This adds a semicircle to the end that has a radius half the width of the line. The line on the right uses the square option. This adds a box with an equal width and half the height of the line thickness.

var ctx = document.getElementById('canvas').getContext('2d');
var lineCap = ['butt','round','square'];

// Draw guides
ctx.strokeStyle = '#09f';
ctx.beginPath();
ctx.moveTo(10,10);
ctx.lineTo(140,10);
ctx.moveTo(10,140);
ctx.lineTo(140,140);
ctx.stroke();

// Draw lines
ctx.strokeStyle = 'black';
for (var i = 0; i < lineCap.length; i++) {
  ctx.lineWidth = 15;
  ctx.lineCap = lineCap[i];
  ctx.beginPath();
  ctx.moveTo(25+i*50,10);
  ctx.lineTo(25+i*50,140);
  ctx.stroke();
}

<canvas id="canvas" width="150" height="150"></canvas>

Screenshot	Live sample

Specifications

Browser compatibility

WebKit/Blink-specific notes

• In WebKit- and Blink-based Browsers, a non-standard and deprecated method ctx.setLineCap() is implemented besides this property.

See also

• The interface defining it, CanvasRenderingContext2D
• CanvasRenderingContext2D.lineWidth
• CanvasRenderingContext2D.lineJoin