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From Aaron Charbonneau <amcha...@gmail.com>
Subject Re: Cordova Screen Capture Plugin for Android
Date Wed, 13 Mar 2013 19:14:20 GMT
Thanks Andrew these are great suggestions!

About not needing the busy-wait in getScreenBits:
I'm not a fan of busy-waiting either.
Perhaps it's a side effect of Jasmine requiring tests to be run and
evaluated synchronously that I decided to use a busy-wait in getScreenBits.
 If the Runnable calls CallbackContext.success/error once the bits are
captured (but not written to file) on the UIThread, the Javascript side
will proceed to run before it has an image url/compare result, most likely
causing that test to fail.  As far as I know Jasmine doesn't allow for
kicking off a bunch of tests and then gather all the results at the end and
output pass/fails (each 'expect' function needs to be within an 'it' block,
essentially that means one test must be evaluated before the next can
begin).

I can see the usefulness of allowing the capture, file io, and comparison
to be able to run asynchronously from the Javascript though. In the case
where you have your own test framework that CAN kick off a bunch of tests
and just gather the results as they come in and do a batch evaluation at
the end, or in the case where you don't want to do any evaluation in your
app and just want to get captures as fast as you can, asynchronous could
increase performance there.

I could try to implement it this way too, if you think that's a worth while
use case, maybe just provide an 'asynchronous' flag in CaptureOptions?

For doing the fileIO/compare using cordova.getThreadPool, is there a
benefit to doing that if I still plan having the operation block the
Javascript?  For asynchronous mode I see why that makes sense.

For the return values, I'll make those changes right away!  Thanks again
for providing your insight, hopefully I understood it correctly.

-Aaron


On Wed, Mar 13, 2013 at 8:04 AM, Andrew Grieve <agrieve@chromium.org> wrote:

> Had a glance at your code. Things you may want to address:
>
> while(!mUIThreadDone) {}
>
> You shouldn't need to busy-wait. Pass the CallbackContext to the Runnable,
> and call success/error on it whenever you're done. No need to have the web
> thread wait for it. Even better would be to use a second Runnable to do the
> image compare / file IO on a background thread via cordova.getThreadPool()
>
> The return value to execute() should only be false if an invalid command
> was passed. It's not meant to indicate the success of the operation. You
> should be returning true for it.
>
> Instead of return "success"/"", it might simplify things a bit to return a
> boolean of true/false
>
>
> On Tue, Mar 12, 2013 at 4:51 PM, Lorin Beer <lorin.beer.dev@gmail.com
> >wrote:
>
> > all the same, very impressive and faster then I expected.
> >
> > - Lorin
> >
> >
> > On Tue, Mar 12, 2013 at 1:46 PM, Aaron Charbonneau <amcharbo@gmail.com
> > >wrote:
> >
> > > Thanks Lorin.
> > >
> > > I did a quick test for throughput on an animating canvas.  I was able
> to
> > > grab 30 frames within a 5 seconds which equates to around 166ms per
> > capture
> > > on a Galaxy Nexus.  Unfortunately not fast enough to automate something
> > > like video.  As with any kind of capturing system, often the overhead
> of
> > > copying bits around is enough to slow down the operation of the app.
> > >
> > > -Aaron
> > >
> > >
> > > On Tue, Mar 12, 2013 at 11:58 AM, Lorin Beer <lorin.beer.dev@gmail.com
> > > >wrote:
> > >
> > > > Hey Aaron,
> > > >
> > > > very cool stuff, looking forward to checking it out!
> > > >
> > > > Question: any performance hit on the app by using Capture? What's the
> > > > expected throughput on images taken in this way (given a particular
> > > device,
> > > > say Galaxy Nexus)?
> > > >
> > > > - Lorin
> > > >
> > > >
> > > > On Tue, Mar 12, 2013 at 11:30 AM, Aaron Charbonneau <
> > amcharbo@gmail.com
> > > > >wrote:
> > > >
> > > > > Glad you like it :)
> > > > > Yes in fact the actual capture makes use of View.capturePicture()
> > which
> > > > > actually grabs the entire document, then that can be clipped down
> to
> > > the
> > > > > size/location of a specific element.
> > > > >
> > > > > -Aaron
> > > > >
> > > > >
> > > > > On Tue, Mar 12, 2013 at 11:27 AM, Michal Mocny <
> mmocny@chromium.org>
> > > > > wrote:
> > > > >
> > > > > > 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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