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Date: Tue, 12 Mar 2013 14:27:40 -0400
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Subject: Re: Cordova Screen Capture Plugin for Android
From: Michal Mocny <mmocny@chromium.org>
To: dev <dev@cordova.apache.org>
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Aaron,

I haven't even begun looking at your implementation, but I'm just going to
say it: this is awesome!

First question: When Capturing a DOM element, can you capture 'body' to
grab it&children for a "full content screenshot", or does it have to be a
specific single element?

-Michal


On Tue, Mar 12, 2013 at 1:58 PM, Aaron Charbonneau <amcharbo@gmail.com>wrote:

> Greetings!  My name is Aaron Charbonneau, happy to be a new member of the
> mailing list!
>
> I have been developing a sceenshot plugin for Cordova to help facilitate
> automation testing and debugging of Cordova apps, and I would love some
> feedback on it.  Currently Cordova provides a bunch of native functions
> that allow you to do some cool stuff, but not much functionality to test
> the apps that make use of them.  Being able to take a capture of the screen
> from within you app is a great way to automate testing or get additional
> information for debugging an issue.  Since there is no
> Javascript mechanism for taking screen captures the solution would have to
> be native, which fits nicely into the "gap" that Cordova/Phonegap bridges.
>  Any medium to large scale app can benefit greatly from automation testing
> and any app can benefit from an extra debugging tool, and that is what I
> hope this screenshot plugin can help achieve.
>
> Currently the plugin offers 2 functions:
>
> Capture():
> * Take a capture of the current view, write that capture to a .png file
> with the specified file name and sub directory of the sdcard (fallback to
> emulated sdcard in the case there isn't an sdcard mounted)
> * Able to create a sub-screenshot with a specified rectangle in order to
> block out ui elements that may be variable, and also save space.
> * Can take captures of images/dom elements (including canvas) that are
> lager than the actual screen size
>
> CaptureAndCompare():
> * All the functionality of Capture()
> * Perform a comparison between the captured image and a baseline image
> located at the specified location in either the assets folder or the
> sdcard.
> * User can specify per color channel tolerances as well as total pixel
> tolerances to avoid false positives for the inevitable rendering
> differences across devices.
> * Optionally output a png file that contains the differences between the
> actual and the baseline for debugging/triage purposes, two modes: binary
> diff (all failing pixels appear as solid white) or the true differences
> between pixels.
>
> If you can spare some time, I would love it if you could take a look at the
> api and parameters I have defined to make sure they adhere to Cordova
> plugin best practices.  The most crucial part would be in the plugin itself
> at ScreenCapture.java:
>
> https://github.com/Charbs09/Cordova-Mobile-Spec-ScreenCapture/blob/master/src/org/apache/cordova/plugin/ScreenCapture.java(capture()
> and captureAndCompare() are the two exposed functions)
>
> I'm also interested to know you thoughts on it's usage.  I started with the
> mobile-spec testing framework and put some quick rendering tests into the
> Autotest section as a viable use case.  In order to get the WebView into
> the state I wanted to capture, I had to implement a wait timer to allow the
> view to update before taking the capture.  Once the wait function
> completes, the capture can be taken and everything from there is callback
> based.  I use the Jasmine waitsFor()/runs() blocks to make the tests run
> synchronously.  For some validation testing I made a compare function in
> Javascript to run against the native compare.  Turns out Java runs alot
> faster than Javascript (surprise!) thus the native compare is about 2-5x
> faster.  All in all the process is fairly quick, the full captureAndCompare
> with 3 file io's takes about 233ms on a Nexus One, and ~100ms on a Nexus 10
> (256x256 image size).
>
> Anyways here is the usage:
>
> https://github.com/Charbs09/Cordova-Mobile-Spec-ScreenCapture/blob/master/assets/www/autotest/tests/rendering.tests.js
>
> And here's the JS wrapper for the plugin calls:
>
> https://github.com/Charbs09/Cordova-Mobile-Spec-ScreenCapture/blob/master/assets/www/screencapture.js
>
> Thanks for your time, and I look forward to ANY feedback positive or
> negative.
>
> Thanks,
> Aaron
>

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