问题
I am trying to plot a group of circles using an HTML5 canvas element (as shown in this image).
The above figure gets cropped when I resize the browser. I want it to be responsive when I resize the browser.
Please help me to make it responsive. Thank you.
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
canvas.width = window.innerWidth; /// equal to window dimension
canvas.height = window.innerHeight;
var radius = canvas.height / 2;
ctx.translate(radius, radius);
radius = radius * 0.9;
drawClock();
function drawClock() {
drawCircle(ctx, radius);
}
function drawCircle(ctx, radius) {
var ang;
var num;
for (num = 1; num <= 40; num++) {
ang = num * Math.PI / 20;
ctx.rotate(ang);
ctx.translate(0, -radius * 0.85);
ctx.rotate(-ang);
ctx.beginPath();
ctx.arc(0, 0, radius / 20, 0, 2 * Math.PI);
ctx.stroke();
ctx.rotate(ang);
ctx.translate(0, radius * 0.85);
ctx.rotate(-ang);
}
}
#canvas {
display: block;
}
<canvas id="canvas"></canvas>
回答1:
The width and height get set when you initialize your canvas element, so you need to listen to the window resize event and reset your canvas width and height.
window.onresize = function() {
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
};
回答2:
If I had this problem, I made this way:
<!DOCTYPE html>
<html>
<head>
<title>expExp.html</title>
<meta http-equiv='Content-Type' content='text/html;charset=utf-8'/>
<script>
var canvas;var ctx;
function fnOL()
{
canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
fnOR();
}
function drawClock() {
var radius;
radius = canvas.height / 2;
ctx.translate(radius, radius);
radius = radius * 0.9;
drawCircle(ctx, radius);
}
function drawCircle(ctx, radius) {
var ang;
var num;
for (num = 1; num <= 40; num++) {
ang = num * Math.PI / 20;
ctx.rotate(ang);
ctx.translate(0, -radius * 0.85);
ctx.rotate(-ang);
ctx.beginPath();
ctx.arc(0, 0, radius / 20, 0, 2 * Math.PI);
ctx.stroke();
ctx.rotate(ang);
ctx.translate(0, radius * 0.85);
ctx.rotate(-ang);
}
}
function fnOR()
{
canvas.width = window.innerWidth; /// equal to window dimension
canvas.height = window.innerHeight;
drawClock();
}
</script>
</head>
<body onload='fnOL();' onresize="fnOR();">
<canvas id='canvas'>No Canvas</canvas><br/>
</body>
</html>
来源:https://stackoverflow.com/questions/38648922/html5-canvas-responsiveness-does-not-work