CanvasRenderingContext2D.lineJoin

The CanvasRenderingContext2D.lineJoin property of the Canvas 2D API determines how two connecting segments (of lines, arcs or curves) with non-zero lengths in a shape are joined together (degenerate segments with zero lengths, whose specified endpoints and control points are exactly at the same position, are skipped).

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

Syntax

ctx.lineJoin = "bevel";
ctx.lineJoin = "round";
ctx.lineJoin = "miter";

Options

There are three possible values for this property: round, bevel and miter. By default this property is set to miter. Note that the lineJoin setting has no effect if the two connected segments have the same direction, because no joining area will be added in this case.

round

Rounds off the corners of a shape by filling an additional sector of disc centered at the common endpoint of connected segments. The radius for these rounded corners is equal to the line width.

bevel

Fills an additional triangular area between the common endpoint of connected segments, and the separate outside rectangular corners of each segment.

miter

Connected segments are joined by extending their outside edges to connect at a single point, with the effect of filling an additional lozenge-shaped area. This setting is effected by the miterLimit property.

Examples

Using the lineJoin property

This is just a simple code snippet using the lineJoin property.

HTML

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

JavaScript

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

ctx.lineWidth = 10;
ctx.lineJoin = "round";
ctx.beginPath();
ctx.moveTo(0,0);
ctx.lineTo(200, 100);
ctx.lineTo(300,0);
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" style="height:120px;">
ctx.lineWidth = 10;
ctx.lineJoin = "round";
ctx.beginPath();
ctx.moveTo(0,0);
ctx.lineTo(200, 100);
ctx.lineTo(300,0);
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 lineJoin example

The example below draws three different paths, demonstrating each of these three lineJoin property settings.

var ctx = document.getElementById('canvas').getContext('2d');
var lineJoin = ['round','bevel','miter'];
ctx.lineWidth = 10;

for (var i = 0; i < lineJoin.length; i++) {
  ctx.lineJoin = lineJoin[i];
  ctx.beginPath();
  ctx.moveTo(-5,5+i*40);
  ctx.lineTo(35,45+i*40);
  ctx.lineTo(75,5+i*40);
  ctx.lineTo(115,45+i*40);
  ctx.lineTo(155,5+i*40);
  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.setLineJoin() is implemented besides this property.

See also

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