CanvasRenderingContext2D.isPointInPath() - Web APIs 编辑

The CanvasRenderingContext2D.isPointInPath() method of the Canvas 2D API reports whether or not the specified point is contained in the current path.

Syntax

ctx.isPointInPath(x, y [, fillRule]);
ctx.isPointInPath(path, x, y [, fillRule]);

Parameters

x

The x-axis coordinate of the point to check, unaffected by the current transformation of the context.

y

The y-axis coordinate of the point to check, unaffected by the current transformation of the context.

fillRule

The algorithm by which to determine if a point is inside or outside the path.
Possible values:

• "nonzero": The non-zero winding rule. Default rule.
• "evenodd": The even-odd winding rule.

path

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

Return value

Boolean

A Boolean, which is true if the specified point is contained in the current or specified path, otherwise false.

Examples

Checking a point in the current path

This example uses the isPointInPath() method to check if a point is within the current path.

HTML

<canvas id="canvas"></canvas>
<p>In path: <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.fill();
result.innerText = ctx.isPointInPath(30, 70);

Result

Checking a point in the specified path

Whenever you move the mouse, this example checks whether the cursor is in a circular Path2D path. If yes, the circle becomes green, otherwise it is red.

HTML

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

JavaScript

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

// Create circle
const circle = new Path2D();
circle.arc(150, 75, 50, 0, 2 * Math.PI);
ctx.fillStyle = 'red';
ctx.fill(circle);

// Listen for mouse moves
canvas.addEventListener('mousemove', function(event) {
  // Check whether point is inside circle
  if (ctx.isPointInPath(circle, event.offsetX, event.offsetY)) {
    ctx.fillStyle = 'green';
  }
  else {
    ctx.fillStyle = 'red';
  }

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

Result

Specifications

Browser compatibility

BCD tables only load in the browser

Gecko-specific note

• Prior to Gecko 7.0 (Firefox 7.0 / Thunderbird 7.0 / SeaMonkey 2.4), this method incorrectly failed to multiply the specified point's coordinates by the current transformation matrix before comparing it to the path. Now this method works correctly even if the context is rotated, scaled, or otherwise transformed.

See also

• The interface defining this method: CanvasRenderingContext2D