HTML canvas globalAlpha property
Examples
First, draw a red rectangle, and then the transparency (globalAlpha) is set 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"
Browser Support
Internet Explorer 9, Firefox, Opera, Chrome and Safari support globalAlpha property.
Note: 8 and earlier versions of Internet Explorer do not support the <canvas> element.
Definition and Usage
globalAlpha property sets or returns the current drawing transparent value (alpha or transparency).
globalAlpha attribute value must be between 0.0 (fully transparent) Digital (opaque) and 1.0.
| Defaults: | 1.0 |
|---|---|
| JavaScript syntax: | context.globalAlpha = number; |
Property Value
| 值 | 描述 |
|---|---|
| number | 透明值。必须介于 0.0（完全透明） 与 1.0（不透明） 之间。 |
HTML canvas Reference Manual