Re: Third time I ask - please help. How to trace visible change in a UIView (UIWebView)
Re: Third time I ask - please help. How to trace visible change in a UIView (UIWebView)
- Subject: Re: Third time I ask - please help. How to trace visible change in a UIView (UIWebView)
- From: David Duncan <email@hidden>
- Date: Mon, 22 Apr 2013 10:39:33 -0700
On Apr 22, 2013, at 10:30 AM, Jens Alfke <email@hidden> wrote:
>
> On Apr 22, 2013, at 12:26 AM, Motti Shneor <email@hidden> wrote:
>
>> I already succeeded in capturing the contents of the view as an image-buffer (out of the CALAyer's context) and I can (brutally) solve my problem by setting up a timer that will sample the view's contents N times a second. However, I'd like to avoid transmitting anything when the view doesn't change
>
> A quick & naive idea is to subclass UIWebView and override -drawRect: to call the inherited method and then set a timer that will capture the view's pixels a fraction of a second later. (You'd want a timer for coalescing purposes, since there are likely to be multiple calls in a short time interval.)
>
> The reason I say this is naive is because UIWebView almost certainly has a whole tree of views inside it that do the actual drawing, so the actual -drawRect: calls are probably going to those instead. But you could give this a try and see if you get anything useful.
Another (likely dealbreaking) downside to this is that its going to call that -drawRect: implementation on every frame of a scroll. Since UIKit does some minimal work even if your -drawRect: is empty, and because you will then also allocate a buffer for the backing store, this is probably not a reasonable tradeoff.
To the greater point the likely reason why you haven't gotten any responses before is simply because what you request is difficult, if not impossible, unless you are acting as the render server itself, which you aren't. Your probably better off doing a timed read and sending diffs to the client instead.
--
David Duncan
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