HTML canvas globalAlphaProperty
Canvas ObjectExample
First, draw a red rectangle, then set the transparency (globalAlpha) to 0.5, and then draw a blue and a green rectangle:
JavaScript：
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.fillStyle="red";
ctx.fillRect(20,20,75,50);
// 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);
var ctx=c.getContext("2d");
ctx.fillStyle="red";
ctx.fillRect(20,20,75,50);
// 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);
Try it yourself »
Browser Support
Internet Explorer 9, Firefox, Opera, Chrome, and Safari support the globalAlpha property.
Note:Internet Explorer 8 and earlier versions do not support the <canvas> element.
Definition and Usage
The globalAlpha property sets or returns 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 (opaque).
| Default value: | 1.0 |
|---|---|
| JavaScript syntax: | context.globalAlpha=number; |
Property Values
| Value | Description |
|---|---|
| number | Transparency value. Must be a number between 0.0 (fully transparent) and 1.0 (opaque). |
Other Extensions