HTML畫布垂直對齊的文本，我們可以使用的textBaseline在畫布范圍內的屬性值。textBaseline可以設置以下值之一 ：top, hanging, middle, alphabetic, ideographic, and bottom。除非另有規定，textBaseline屬性默認為字母。
context.textBaseline=[value];
<!DOCTYPE HTML>
<html>
<head>
<title>html5_canvas_text_baseline</title>
<style>
body {margin: 0px;padding: 0px;}
#myCanvas {border: 1px solid #9C9898; margin:0 auto;margin-top:200px; margin-left:100px;}
</style>
<script>
window.onload = function(){
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var x = canvas.width / 2;
var y = canvas.height / 2;
context.font = "30pt Calibri";
// textAlign aligns text horizontally relative to placement
context.textAlign = "center";
// textBaseline aligns text vertically relative to font style
context.textBaseline = "middle";
context.fillStyle = "blue";
context.fillText("Hello World!", x, y);
};
</script>
</head>
<body>
<canvas id="myCanvas" width="578" height="200">
</canvas>
</body>
</html>
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