CanvasRenderingContext2D: drawFocusIfNeeded() method
The
CanvasRenderingContext2D.drawFocusIfNeeded()
method of the Canvas 2D API draws a focus ring around the current or given path, if the
specified element is focused.
Syntax
js
drawFocusIfNeeded(element)
drawFocusIfNeeded(path, element)
Parameters
element
-
The element to check whether it is focused or not.
path
-
A
Path2D
path to use.
Return value
None (undefined
).
Examples
Managing button focus
This example draws two buttons on a canvas. The drawFocusIfNeeded()
method
is used to draw a focus ring when appropriate.
HTML
html
<canvas id="canvas">
<button id="button1">Continue</button>
<button id="button2">Quit</button>
</canvas>
JavaScript
js
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
const button1 = document.getElementById("button1");
const button2 = document.getElementById("button2");
document.addEventListener("focus", redraw, true);
document.addEventListener("blur", redraw, true);
canvas.addEventListener("click", handleClick, false);
redraw();
function redraw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawButton(button1, 20, 20);
drawButton(button2, 20, 80);
}
function handleClick(e) {
// Calculate click coordinates
const x = e.clientX - canvas.offsetLeft;
const y = e.clientY - canvas.offsetTop;
// Focus button1, if appropriate
drawButton(button1, 20, 20);
if (ctx.isPointInPath(x, y)) {
button1.focus();
}
// Focus button2, if appropriate
drawButton(button2, 20, 80);
if (ctx.isPointInPath(x, y)) {
button2.focus();
}
}
function drawButton(el, x, y) {
const active = document.activeElement === el;
const width = 150;
const height = 40;
// Button background
ctx.fillStyle = active ? "pink" : "lightgray";
ctx.fillRect(x, y, width, height);
// Button text
ctx.font = "15px sans-serif";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.fillStyle = active ? "blue" : "black";
ctx.fillText(el.textContent, x + width / 2, y + height / 2);
// Define clickable area
ctx.beginPath();
ctx.rect(x, y, width, height);
// Draw focus ring, if appropriate
ctx.drawFocusIfNeeded(el);
}
Result
Specifications
Specification |
---|
HTML Standard # dom-context-2d-drawfocusifneeded-dev |
Browser compatibility
BCD tables only load in the browser
See also
- The interface defining this method:
CanvasRenderingContext2D