How do I check how much of a Canvas.AsJson is transparent?

I'm struggling with the Canvas plugin to check in percentage how much of a Canvas is transparent loading the Canvas.AsJson expression in an Array every 1 second.

Here's a bit of info about the .asJson expression for the canvas:

And here's how to do it:

global number pixelCount = 0

global number percentClear = 0

every 1.0 seconds

--- array: load from canvas.asJSON

--- set pixelCount to 0

------ repeat canvas.width*canvas.height times

------ Array at (0,0,loopindex*4+3) = 0

--------- add 1 to pixelCount

--- set percentClear to pixelCount/canvas.width*canvas.height

In the array comparison instead of checking if the alpha is 0 you could for instance use <128 to count any pixel less than 50% trasparent.

Demo: http://yaserahmady.com/razor/

Thanks R0J0hound but that was the exact same thing I've done, at least I think it was as I don't quite understand the textual representation of the events' flow.

The problem was apparently because

pixelCount/canvas.width*canvas.height[/code:u6nw2nwf] gave me an incredibly off result. So I threw in some brackets [code:u6nw2nwf]pixelCount/(canvas.width*canvas.height)[/code:u6nw2nwf] and it magically worked. That's not what I learnt in elementary school. I'm sorry if I didn't explain thoroughly my problem.

[img="http://i.imgur.com/LhKQcBT.png"]

Could I ask you why this lags every time I do the check and why there are two Canvas.AsJSON?

[img="http://i.imgur.com/X0C5HBw.png"]

My event sheet.
[img="http://i.imgur.com/5QNmCiJ.png"]

Good catch with the parenthesis, multiplication and division are done left to right. I think I learned about that in basic algebra.

It's slow because between the .asJSON expression and loading it into an array it's a slow operation. I haven't really seen a way to make it faster.

There are two asJSON expressions because all objects have that expression to get a json version of their state. For canvas object they both do the same thing.