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?
我认为这将解决您的问题
ctx.fillStyle = "rgba(255, 255, 255, 0.5)";
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.
尝试 ctx.canvas.width,而不是 ctx.width
Has your problem been solved
I encountered this problem while using Windows computer
I used opacity: .99
solved this problem
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