CanvasRenderingContext2D.drawFocusIfNeeded()
CanvasRenderingContext2D.drawFocusIfNeeded()
是 Canvas 2D API 用来给当前路径或特定路径绘制焦点的方法,如果给定的元素获取了焦点。
语法
void ctx.drawFocusIfNeeded(element); void ctx.drawFocusIfNeeded(path, element);
参数
- element
-
是否需要设置焦点的元素。
path
-
Path2D
路径。
示例
控制按钮焦点
这是一段使用 drawFocusIfNeeded
方法的简单的代码片段。
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);
}
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
- 接口定义,
CanvasRenderingContext2D
.