Transparency context.fill style in canvas html5 [closed]

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I write this javascript code :

context.shadowOffsetX = 5;
context.shadowOffsetY = 5;
context.shadowBlur = 4;
context.shadowColor = 'rgba(255, 0, 0, 0.5)';
context.fillStyle = '#f00';
context.fillRect(x, y, w, h);

I add this script on a photo , I want see the color of image , but can not add transparency to this script .

回答1:

Try making the fillStyle RGBA, too.

context.fillStyle = 'rgba(255, 0, 0, 0.5)';
context.fillRect(x, y, w, h);

来源：https://stackoverflow.com/questions/19132064/transparency-context-fill-style-in-canvas-html5