CanvasRenderingContext2D:drawFocusIfNeeded() 方法
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
Canvas 2D API 的 CanvasRenderingContext2D.drawFocusIfNeeded()
方法用于当指定的元素处于焦点状态时在当前或指定路径周围绘制焦点环。
语法
js
drawFocusIfNeeded(element)
drawFocusIfNeeded(path, element)
参数
返回值
无(undefined
)。
示例
管理按钮焦点
这个例子在画布上绘制了两个按钮。使用 drawFocusIfNeeded()
方法在适当的时候绘制焦点环。
HTML
html
<canvas id="canvas">
<button id="button1">继续</button>
<button id="button2">退出</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) {
// 计算点击坐标
const x = e.clientX - canvas.offsetLeft;
const y = e.clientY - canvas.offsetTop;
// 如果合适,聚焦 button1
drawButton(button1, 20, 20);
if (ctx.isPointInPath(x, y)) {
button1.focus();
}
// 如果合适,聚焦 button2
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;
// 按钮背景
ctx.fillStyle = active ? "pink" : "lightgray";
ctx.fillRect(x, y, width, height);
// 按钮文本
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);
// 定义可点击区域
ctx.beginPath();
ctx.rect(x, y, width, height);
// 如果合适,绘制焦点环
ctx.drawFocusIfNeeded(el);
}
结果
规范
Specification |
---|
HTML Standard # dom-context-2d-drawfocusifneeded-dev |
浏览器兼容性
BCD tables only load in the browser
参见
- 定义此方法的接口:
CanvasRenderingContext2D