如何使用javascript将html 5画布居中

Question

我正在尝试使用javascript将动态html 5画布窗口居中。 我知道我的代码不起作用，但我想知道是否有一种方法可以实现margin-left：auto / margin-left：auto技术，通常将元素放在html页面中。 我也用我的画布类css尝试了这个，这也不起作用所以任何帮助都是值得赞赏的。 谢谢。

我的代码：

var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");


document.getElementById("canvas").style.marginLeft = "auto";
document.getElementById("canvas").style.marginRight = "auto";

canvas.width = 300;
canvas.height = 300;
drawScreen();

formElement = document.getElementById("height");
formElement.addEventListener('change', heightChanged, true);

formElement = document.getElementById("width");
formElement.addEventListener('change', widthChanged, false);

function widthChanged(e) {
  var target = e.target;
  canvas.width = target.value;
  drawScreen();
}

function heightChanged(e) {
  var target = e.target;
  canvas.height = target.value;
  drawScreen();
}

function drawScreen() {
}

Answer 1

使画布成为块级元素。 您可以使用CSS或将此行添加到您的代码中：

canvas.style.display= 'block';

例：

 var canvas = document.getElementById("canvas"); var context = canvas.getContext("2d"); document.getElementById("canvas").style.marginLeft = "auto"; document.getElementById("canvas").style.marginRight = "auto"; canvas.style.display= 'block'; canvas.width = 300; canvas.height = 300; drawScreen(); formElement = document.getElementById("height"); formElement.addEventListener('change', heightChanged, true); formElement = document.getElementById("width"); formElement.addEventListener('change', widthChanged, false); function widthChanged(e) { var target = e.target; canvas.width = target.value; drawScreen(); } function heightChanged(e) { var target = e.target; canvas.height = target.value; drawScreen(); } function drawScreen() { } 

 canvas { border: 1px solid black; background: yellow; } 

 <canvas id="canvas"></canvas> <div id="height"></div> <div id="width"></div> 

Answer 2

你喜欢用css ：

canvas {
        display: block;
        position: absolute;
        margin: auto;
        top: 0;
        bottom: 0;
        left: 0;
        right: 0;
    }

或使用javascript ：

 document.getElementById("canvas").style.display = "block";
        document.getElementById("canvas").style.margin = "auto";
        document.getElementById("canvas").style.position = "absolute";
        document.getElementById("canvas").style.top = 0;
        document.getElementById("canvas").style.bottom = 0;
        document.getElementById("canvas").style.left = 0;
        document.getElementById("canvas").style.right = 0;

现场演示

Answer 3

你为什么不把画布放入div容器？

你也可以通过javascript来做到这一点。

var container = document.createElement("div");
container.style.marginLeft = "auto";
container.style.marginRight = "auto";
container.style.width = "300px";

container.innerHtml = canvas;