CanvasRenderingContext2D.lineCap

The CanvasRenderingContext2D.lineCap property of the Canvas 2D API determines the shape used to draw the end points of lines.

Syntax

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

Options

"butt"

The ends of lines are squared off at the endpoints. Default value.

"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(20, 20);
ctx.lineWidth = 15;
ctx.lineCap = 'round';
ctx.lineTo(100, 100);
ctx.stroke();

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

Comparison of line caps

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 (let 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();
}

Specifications

Browser compatibilityUpdate compatibility data on GitHub

WebKit/Blink-specific notes

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

See also

• The interface defining this property: CanvasRenderingContext2D
• CanvasRenderingContext2D.lineWidth
• CanvasRenderingContext2D.lineJoin