canvas fillStyle in interval with transparent/opacity

Question

This small code clear old canvas data in interval:

// start interval ctx.save();     ctx.fillStyle = "rgba(0, 0, 0, 0.2)";     ctx.fillRect(0, 0, ctx.width, ctx.height); ctx.restore(); //some draw code for new graph ... //end interval 

My work area become black, because i set black as fill color ( rgba(0, 0, 0, .2) ), but I need a transparent background, not black.

I tried use globalAlpha and imagePutData but i failed.

How i can do this?

Answer 1

I think this will resolve your issue

ctx.fillStyle = "rgba(255, 255, 255, 0.5)"; 

Answer 2

Using an rgba(0,0,0,.2) fillStyle and fillRect() works for me on both chrome and firefox - it paints a semi-transparent black fill. Check to make sure you're not doing something else that's causing a fully opaque paint of some sort.