CanvasRenderingContext2D.lineJoin - Web APIs 编辑

The CanvasRenderingContext2D.lineJoin property of the Canvas 2D API determines the shape used to join two line segments where they meet.

This property has no effect wherever two connected segments have the same direction, because no joining area will be added in this case. Degenerate segments with a length of zero (i.e., with all endpoints and control points at the exact same position) are also ignored.

Note: Lines can be drawn with the stroke(), strokeRect(), and strokeText() methods.

Syntax

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

Options

There are three possible values for this property: "round", "bevel", and "miter". The default is "miter".

"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 affected by the miterLimit property. Default value.

Examples

Changing the joins in a path

This example applies rounded line joins to a path.

HTML

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

JavaScript

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

ctx.lineWidth = 20;
ctx.lineJoin = 'round';
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(190, 100);
ctx.lineTo(280, 20);
ctx.lineTo(280, 150);
ctx.stroke();

Result

Comparison of line joins

The example below draws three different paths, demonstrating each of the three lineJoin options.

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

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

for (let 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();
}

Screenshot	Live sample

Specifications

Browser compatibility

BCD tables only load in the browser

WebKit/Blink-specific notes

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

See also

• The interface defining this property: CanvasRenderingContext2D
• CanvasRenderingContext2D.lineCap
• CanvasRenderingContext2D.lineWidth
• Applying styles and color