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HTML5 canvas globalAlpha Attribute

HTML5 track Tag Reference HTML5 canvas reference

Example

Draw a red and a blue rectangle, where the blue rectangle is transparent:

JavaScript:

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.fillStyle="red";
ctx.fillRect(20,20,75,50);
ctx.fillStyle="blue";
ctx.globalAlpha=0.2;
ctx.fillRect(50,50,75,50);

Try it yourself »

Definition and Usage

The globalAlpha attribute specifies the transparency of the drawings.

The globalAlpha attribute value can be a number between 0 and 1.

0=full transparency, 1=no transparency.

Default value:	0
JavaScript syntax:	context.globalAlpha=0.5;

Browser Support

The globalAlpha attribute is supported in all major browsers.

Attribute Values

Value	Description	Play it
number	Specifies the transparency. Must be a number between 0 and 1	Play it »