[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michi Henning]

** Changed in: thumbnailer (Ubuntu)
   Status: New => Invalid

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Title:
  Lots of thumbnail requests with invalid size

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Launchpad Bug Tracker]

This bug was fixed in the package unity8 - 8.11+15.10.20150915-0ubuntu1

---
unity8 (8.11+15.10.20150915-0ubuntu1) wily; urgency=medium

  [ Albert Astals Cid ]
  * Fix testNotifications
  * Make the wait longer to make tests pass in CI
  * New simplified CroppedImageMinimumSourceSize (LP: #1467740)
  * Stop animateTimer when starting the fadeOutAnimation
  * Use  AlreadyLaunchedUpstart so that tests passes
  * Workaround keyboard issues and make test pass again

  [ Daniel d'Andrada ]
  * DesktopStage: Refactor focus handling
  * Stabilize tstShell.test_launchedAppHasActiveFocus

  [ Gary.Wzl ]
  * Add widgetData["expanded"] property for expandable widget.

  [ Michael Terry ]
  * Fix typo that caused the tutorial to tease the launcher on top of
the greeter.
  * Fix typo that caused the tutorial to tease the launcher on top of
the greeter.

 -- Michael Zanetti   Tue, 15 Sep 2015
12:06:06 +

** Changed in: unity8 (Ubuntu)
   Status: New => Fix Released

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Title:
  Lots of thumbnail requests with invalid size

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Launchpad Bug Tracker]

** Branch linked: lp:ubuntu/wily-proposed/unity8

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  Lots of thumbnail requests with invalid size

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Albert Astals Cid]

Ok,
https://code.launchpad.net/~aacid/unity8/newCroppedImageMinimumSourceSize/+merge/269233
should solve the problems in the unity8 side

** Branch linked: lp:~aacid/unity8/newCroppedImageMinimumSourceSize

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Title:
  Lots of thumbnail requests with invalid size

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Albert Astals Cid]

 I don't quite understand why you need to know the aspect ratio beforehand. 
 Surely, there must be some display size into which the thumbnail is expected 
 to fit?

Ok, let's give you an example.

I know i have to fit my image in something that is 100 width x 100
height and i am using the PreserveAspectCrop fill format meaning the
image is scaled uniformly to fill, cropping if necessary

If i don't know the aspect ratio of the image that i have to draw which
size do i request?

If the image is portrait i have to request (100, 0)

If the image is landscape i have to request (0, 100)

See http://paste.ubuntu.com/12197917/ using
http://i.imgur.com/xiP0k4T.jpg as landscape.jpg and
http://i.imgur.com/A2M6bnF.jpg as portrait.jpg and you'll see
http://i.imgur.com/f5sEMhe.png. You can see there why we need to know
the aspect ratio to achive the best quality. In the first row Source
Size Width has the best quality while in the second row Source Size
Height has the best quality.

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Title:
  Lots of thumbnail requests with invalid size

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michał Sawicz]

Just to chime in, I believe this just shows an issue with the API as it
stands today - it'd be best if we could supply the minimum width/height
and have the other end (thumbnailer in this case) determine what to do.

But I agree with Albert, for now to comply with the API, undefined
sourceSize needs to be supported, and return the natural image with no
scaling.

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Title:
  Lots of thumbnail requests with invalid size

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[James Henstridge]

To be clear, what I suggested was to use the height and width unchanged
rather than multiplying by 4: that would improve the quality over the
current code while not blowing out the memory requirements of providing
huge images.

As a longer term solution to get images of the required quality, I
suggested the following on IRC:

We've got enough information on the back end to provide an image of the
proper size so it can be cropped to the desired dimensions without
scaling.  So the idea is to do something like this:

1. If the dash sees a URI like image://albumart, artistart or thumbnailer, add 
a crop=1 parameter to the end before using it as the source for the Image, and 
set sourceSize to the the cropped image dimensions.
2. In the image provider, if the crop parameter is included, interpret 
requestedSize as the desired crop dimensions rather than a bounding box.
3. return an image that can be cropped to those dimensions without scaling.

Qt already seems to handle the case when an image provider returns an
image larger than requestedSize, so I imagine this would work okay.

This is a bit of a hack, but no more so than the whole
CroppedImageMinimumSourceSize component.  I agree that it'd be nice if
Qt made it easier to load an image at an appropriate size to use with
PreserveAspectCrop.

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Albert Astals Cid]

https://code.launchpad.net/~aacid/unity8/cropped_image_unknown_aspect_ratio/+merge/269185
implements the suggest workaround by James, it's not terrible, but makes
us use more memory than needed to get an acceptable quality.

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Title:
  Lots of thumbnail requests with invalid size

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michi Henning]

I haven't thought this through fully yet, but I think I agree with
James. It should be possible for us to deliver an image that is x pixels
wide/tall in its smaller dimension, rather than only delivering images
that that are no bigger than x pixels in their larger dimension (which
is what we are providing now).

I'd expect that we'd still return images that are possibly smaller than
what was asked for (as we do now), because upscaling is a policy
decision that should be up to the application, not the thumbnailer.

James and I can discuss this.

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Title:
  Lots of thumbnail requests with invalid size

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Albert Astals Cid]

 Well, consider the cost of scaling down from a full-size photo to a 
 thumbnail. It takes a quarter of a second on a Nexus 4.
Yes, that should be done as few times as possible.

 Surely, it's not too much to ask the caller what size thumbnail it wants?
It actually is, i have no idea of the image i want unless you tell me the 
aspect ratio and since i can't know the aspect ratio i need the full image.

  The meaning of (-1, -1) is I don't know what I need, just give me something.
You're making this up, the API documentation explicitly says sourceSize can be 
cleared to the natural size of the image by setting sourceSize to undefined.

 The point here is that the thumbnailer has no business setting policy.
You say you have no business setting the policy but then go and set a policy 
that says i'm not accepting undefined sizes even if the API says i should, 
please do not do that.

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michi Henning]

Correction: the old thumbnailer returned 128x128 for QSize(-1,-1), not
512x512.

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[James Henstridge]

I think this is actually on the Unity8 side rather than unity-scopes-
shell.

The result cards are generated by CardCreator.js, which uses a
CroppedImageMinimumSourceSize component to display the result art:

http://bazaar.launchpad.net/~unity-
team/unity8/trunk/view/head:/plugins/Dash/CardCreator.js#L101

This component is implemented in QML but delegates finding the size of
the image to the C++ component CroppedImageSizer

http://bazaar.launchpad.net/~unity-
team/unity8/trunk/view/head:/plugins/Dash/CroppedImageMinimumSourceSize.qml

That class uses QNetworkAccessManager to try and get the file contents
and uses a helper class to manage the response:

http://bazaar.launchpad.net/~unity-
team/unity8/trunk/view/head:/plugins/Dash/croppedimagesizer.cpp#L102

That helper tries to read the returned data via QImageReader and passes
the image size back to CroppedImageSizer:

http://bazaar.launchpad.net/~unity-
team/unity8/trunk/view/head:/plugins/Dash/croppedimagesizerasyncworker.cpp#L58

If the worker provides a non-empty size, CroppedImageSizer then uses
that size information to pick a sourceSize value that will result in the
image being loaded at the correct size so it only has to be cropped in
at most one dimension to fit.  If an empty (or invalid) size is
provided, it sets sourceSize to (0, 0):

http://bazaar.launchpad.net/~unity-
team/unity8/trunk/view/head:/plugins/Dash/croppedimagesizer.cpp#L118

This causes a problem for the thumbnailer because QNetworkAccessManager
has no idea how to deal with image:// URIs, so we get an invalid QSize
from the worker and use a sourceSize of (0, 0).  Perhaps it should just
use the requested dimensions in this case instead.  It doesn't look like
there is a way to handle this crop mode properly with
QQuickImageProvider.

** Package changed: unity-scopes-shell (Ubuntu) = unity8 (Ubuntu)

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Albert Astals Cid]

I don't understand why you guys consider an undefined size to be
invalid, the documentation of Qt is quite clear in that it is a valid
size


sourceSize can be cleared to the natural size of the image by setting 
sourceSize to undefined.


So yes I want the natural size of the image if i can't find out what's
the aspect ratio of the image. Besides it's weird because you complain
for undefined but for 0x0 you give me a thumbnail just fine.

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michi Henning]

Well, consider the cost of scaling down from a full-size photo to a
thumbnail. It takes a quarter of a second on a Nexus 4.

Surely, it's not too much to ask the caller what size thumbnail it
wants? If we are not told what size the caller needs, we can either
deliver the full-size image, which is really expensive and eats a lot of
disk space, or we can deliver some thumbnail that is arbitrarily smaller
and ends up getting scaled up and looking bad. Either the battery loses
or the user experience loses.

The meaning of (0, 0) is give me the best thumbnail available. We'll
faithfully do that. We ask that callers use this feature judiciously
because it is expensive. The meaning of (-1, -1) is I don't know what I
need, just give me something. I don't think that's a good idea, and we
should never have supported that feature in the first place. If the
caller doesn't know what size image it needs, there is a problem with
the caller, I think.

If the caller doesn't mind scaling up and the loss of image quality, it
is free to ask for (256, 256) or whatever, and we'll provide that. The
point here is that the thumbnailer has no business setting policy. The
policy is up to the caller.

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michi Henning]

So, here is some history of this. The old thumbnailer, when presented
with (-1,-1), delivered a 512 thumbnail. That wasn't really by design,
but a side-effect of how the code was written. When we changed to the
new thumbnailer, we decided to return the full-size image for an invalid
QSize.

That turned out to be a mistake: when we ran a bunch of apps and scopes
against the new thumbnailer, we found that there were lots of cases were
the caller passed an uninitialized QSize, and we returned a full-size
image in response. To the caller, everything appears to be working
correctly, but it's working horribly inefficiently, both in terms of
disk space and in terms of scaling.

If the caller wants a full-size image, it can do that, by asking for (0,
0). The advantage is that asking for a full-size image becomes an
explicit operation, so it won't happen by accident.

I don't quite understand why you need to know the aspect ratio
beforehand. Surely, there must be some display size into which the
thumbnail is expected to fit? If we get something like QSize(512, 0) or
(0, 512), we assume a 512x512 bounding box and scale accordingly. (We
always preserve aspect ratio.) So, why not use that? And, if you really
want a full-size image, just ask for (0,0) and you'll get it. But we
can't return a full-size image for an uninitialized QSize; all that does
is hide errors and it causes things to run horribly inefficiently.

Returning some other size for (-1,-1) will be wrong most of the time for
most callers, no matter what size we pick. It'll be too small and look
bad, or it'll be too large and inefficient.

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michi Henning]

** Changed in: unity-scopes-shell (Ubuntu)
   Status: New = Invalid

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michi Henning]

** Changed in: unity-scopes-shell (Ubuntu)
   Status: Invalid = New

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[Bug 1467740] Re: Lots of thumbnail requests with invalid size

[Michi Henning]

** Tags added: invalid-qsize

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