CanvasRenderingContext2D.isPointInStroke() - Web APIs 编辑

The CanvasRenderingContext2D.isPointInStroke() method of the Canvas 2D API reports whether or not the specified point is inside the area contained by the stroking of a path.

Syntax

ctx.isPointInStroke(x, y);
ctx.isPointInStroke(path, x, y);

Parameters

x

The x-axis coordinate of the point to check.

y

The y-axis coordinate of the point to check.

path

A Path2D path to check against. If unspecified, the current path is used.

Return value

Boolean

A Boolean, which is true if the point is inside the area contained by the stroking of a path, otherwise false.

Examples

Checking a point in the current path

This example uses the isPointInStroke() method to check if a point is within the area of the current path's stroke.

HTML

<canvas id="canvas"></canvas>
<p>In stroke: <code id="result">false</code></p>

JavaScript

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

ctx.rect(10, 10, 100, 100);
ctx.stroke();
result.innerText = ctx.isPointInStroke(50, 10);

Result

Checking a point in the specified path

Whenever you move the mouse, this example checks whether the cursor is in the stroke of an elliptical Path2D path. If yes, the ellipse's stroke becomes green, otherwise it is red.

HTML

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

JavaScript

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

// Create ellipse
const ellipse = new Path2D();
ellipse.ellipse(150, 75, 40, 60, Math.PI * .25, 0, 2 * Math.PI);
ctx.lineWidth = 25;
ctx.strokeStyle = 'red';
ctx.fill(ellipse);
ctx.stroke(ellipse);

// Listen for mouse moves
canvas.addEventListener('mousemove', function(event) {
  // Check whether point is inside ellipse's stroke
  if (ctx.isPointInStroke(ellipse, event.offsetX, event.offsetY)) {
    ctx.strokeStyle = 'green';
  }
  else {
    ctx.strokeStyle = 'red';
  }

  // Draw ellipse
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.fill(ellipse);
  ctx.stroke(ellipse);
});

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The interface defining this method: CanvasRenderingContext2D