ClearClick Algorithm explanation

[Naman]

Hi,
I was going through ClickClick module of NoScript. I found a draft online describing it's algorithm. Can someone tell me what is the business of the snapshots and there comparisons. Because in experiments, I always get a warning when opacity attribute is below 0.3 otherwise it make it fully visible and perform action according to click.
Any help will be highly appreciated.

Thanks.

[Giorgio Maone]

The draft online refers to an opt-in (from the server side) method, to be standardized by the W3C and made available in browsers, that since is opt-in can be made stricter (e.g. no opacity tolerance).
The arbitrary 0.3 opacity threshold in NoScript has been choosen because it should allow users to see what's going on, therefore no need for a ClearClick warning.

[Naman]

So it means , currently ClearClick only sees opacity? if user clicks on an iframe with opacity less than 0.3 generate an alert otherwise perform action event? If not what do you mean by Opt-In (from server-side) method?

[Giorgio Maone]

So it means , currently ClearClick only sees opacity?

Nope. NoScript takes two screenshots, so by whatever means you obstruct the click target it will be detected.
The .3 opacity threshold is just used to decide whether some elements are to be ignored as an obstacle, because they're so transparent that user can anyway see what's behind them (they're likely to be just decorations).

[Naman]

Ok thanks. I got it now. But I think it's a good idea to generate ALERT only when there are two overlapping(at same coordinates) clickable (link, button, text, image etc) elements inside the page and opacity of iframe is below say 0.3. Isn't it? It may reduce its false positive significantly.