CanvasRenderingContext2D.drawFocusIfNeeded()

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句法
范例
规范
浏览器兼容性
另请参阅
相关话题

CanvasRenderingContext2D .drawFocusIfNeeded() method of the Canvas 2D API draws a focus ring around the current or given path, if the specified element is focused.

句法

void ctx.drawFocusIfNeeded(element);
void ctx.drawFocusIfNeeded(path, element);

参数

element
path: Path2D path to use.

范例

Managing button focus

This example draws two buttons on a canvas. The drawFocusIfNeeded() method is used to draw a focus ring when appropriate.

HTML

<canvas id="canvas">
  <button id="button1">Continue</button>
  <button id="button2">Quit</button>
</canvas>

JavaScript

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);
}

结果

规范

规范	状态	注释
HTML 实时标准 The definition of 'CanvasRenderingContext2D.drawFocusIfNeeded' in that specification.	实时标准	初始定义

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`drawFocusIfNeeded`	Chrome Yes	Edge 14	Firefox 32 32 29 Disabled Disabled From version 29: this feature is behind the `canvas.focusring.enabled` preference. To change preferences in Firefox, visit about:config. 28 Alternate Name Alternate Name Uses the non-standard name: `drawSystemFocusRing`	IE No	Opera Yes	Safari Yes	WebView Android Yes	Chrome Android Yes	Firefox Android 32 32 29 Disabled Disabled From version 29: this feature is behind the `canvas.focusring.enabled` preference. To change preferences in Firefox, visit about:config. 28 Alternate Name Alternate Name Uses the non-standard name: `drawSystemFocusRing`	Opera Android Yes	Safari iOS Yes	Samsung Internet Android Yes
`路径` 参数	Chrome Yes	Edge ≤79	Firefox No	IE No	Opera Yes	Safari Yes	WebView Android Yes	Chrome Android Yes	Firefox Android No	Opera Android Yes	Safari iOS Yes	Samsung Internet Android Yes

图例

完整支持
不支持
用户必须明确启用此特征。

另请参阅

The interface defining this method: CanvasRenderingContext2D

元数据

最后修改： Aug 6, 2020

在此页

句法

参数

范例

Managing button focus

HTML

JavaScript

结果

规范

浏览器兼容性

图例

另请参阅

相关话题