HTML canvas globalAlpha Property

Introduction

Draw a red rectangle, then set transparency (globalAlpha) to 0.5, and then draw a blue and a green rectangle:

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<!DOCTYPE html>
<html>
<body>

<canvas id="myCanvas" width="300" height="180" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>

<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "red";
ctx.fillRect(20, 20, 75, 50);/*w  w w.  ja  va  2  s .c  om*/

// Turn transparency on
ctx.globalAlpha = 0.2;
ctx.fillStyle = "blue";
ctx.fillRect(50, 50, 75, 50);
ctx.fillStyle = "green";
ctx.fillRect(80, 80, 75, 50);
</script>

</body>
</html>

The globalAlpha property sets or gets the current alpha or transparency value of the drawing.

The globalAlpha property value must be a number between 0.0 (fully transparent) and 1.0 (no transparency).

Default value: 1.0 

context.globalAlpha = number;



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