書式
コンテキスト.globalAlpha
説明
不透明度を指定します。
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Sample</title>
<script>
window.onload = function(){
var canvasObj = document.getElementById("imgCanvas");
var context = canvasObj.getContext("2d");
context.fillStyle = "rgba(255,0,0,1)";
context.fillRect(20,40,200,50);
context.globalAlpha = 0.5;
context.fillRect(20,100,200,50);
context.globalAlpha = 0.25;
context.fillRect(20,160,200,50);
}
</script>
</head>
<body>
<h1>Sample</h1>
<canvas id="imgCanvas" width="320" height="240" style="border:1px black solid"></canvas>
</body>
</html>