Support providing fallback images

[James Henstridge]

If the URI for a scope result icon can not be loaded, the scope result is not easily visible.

To counter this, the shell should replace the result image with a fallback image if the Image QML component changes to the Error state. At a minimum a single standard fallback image would be sufficient, but letting the scope pick a custom fallback via the category renderer template would be better.

One reason I'd like to see this is so we can switch the album art image provider to stop returning a fallback image. This has been requested by the music-app guys, and seems sensible since we might want different fallbacks in different contexts:

https://code.launchpad.net/~jamesh/thumbnailer/no-fallback-albumart/+merge/219460

It might also be useful for remote scopes using http: URIs for result icons.

[James Henstridge (jamesh)]

When this is fixed, we'll need to remove the fixed fallback in the artist art image provider too.

[Thomas Strehl (strehl-t)]

Michi: what was the proposed solution here? Providing a default fallback, with the scope being able to override the fallback per category?

[Michi Henning (michihenning)]

Hmmm... I guess it'll need to happen as part of the category renderer template, so the scope can nominate a preferred fallback image. The rest of it (making sure the fallback image is displayed when album art or some such can't be retrieved, or substituting a default fallback image if the scope hasn't specified one) is up to the shell.

I can work on this next week, if you like. I don't think it'll be difficult. I left this alone mainly because the bulk of the work could be done by the shell already. All it needs to do is display *something* when a request to retrieve artwork fails. Allowing the scope to specify a custom fallback image is just icing on the cake…

Cheers,

Michi.

On 11 Dec 2014, at 20:47 , Thomas Strehl <email address hidden> wrote:

> Michi: what was the proposed solution here? Providing a default
> fallback, with the scope being able to override the fallback per
> category?
>
> --
> You received this bug notification because you are subscribed to unity-
> scopes-api in Ubuntu.
> https://bugs.launchpad.net/bugs/1324142
>
> Title:
> Support providing fallback images
>
> Status in Thumbnail generator for all kinds of files:
> New
> Status in unity-scopes-api package in Ubuntu:
> New
> Status in unity-scopes-shell package in Ubuntu:
> New
> Status in unity8 package in Ubuntu:
> Triaged
>
> Bug description:
> If the URI for a scope result icon can not be loaded, the scope result
> is not easily visible.
>
> To counter this, the shell should replace the result image with a
> fallback image if the Image QML component changes to the Error state.
> At a minimum a single standard fallback image would be sufficient, but
> letting the scope pick a custom fallback via the category renderer
> template would be better.
>
> One reason I'd like to see this is so we can switch the album art
> image provider to stop returning a fallback image. This has been
> requested by the music-app guys, and seems sensible since we might
> want different fallbacks in different contexts:
>
> https://code.launchpad.net/~jamesh/thumbnailer/no-fallback-
> albumart/+merge/219460
>
> It might also be useful for remote scopes using http: URIs for result
> icons.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/thumbnailer/+bug/1324142/+subscriptions

[Michi Henning (michihenning)]

It looks like all that's really needed on the scopes side is a documentation update. I've documented a "art-fallback" in the "components" dictionary of the category renderer. That allows a scope to specify a category-specific fallback image. I think this should be enough of a hook, but the shell will need to actually use the field if it cannot retrieve the artwork for a particular result. If no fallback image is specified, or the URI for the fallback image cannot be resolved, I guess the shell should display some universal placeholder image, so there is at least something on screen, instead of nothing at all.

[Michi Henning (michihenning)]

It looks like, over time, a number of additional fields have crept into the JSON, most likely because scope authors and the shell have made gentlemen's agreements. This includes (at least), mascot, emblem, attributes, summary, background, and overlay-color. It also looks like there are result-specific settings (such as mascot) that are undocumented, and for which there is no accessor/setter in the Result or SearchResult classes.

We need to construct a definitive list of which fields are used by the shell, both per-category and per-result, so we can document them. Otherwise, all these features will remain inaccessible to outside scope authors.

As discussed with Saviq on IRC, he'll find someone who can construct this list by inspecting the shell code, so we can update the scopes documentation accordingly.

In future, whenever the shell interprets something new in the JSON, or changes the meaning of an existing entry, we'll need to raise a bug with scopes-api so we can update the doc.

[Michi Henning (michihenning)]

Saviq just told me the following: "art", "summary", "background", "title", "mascot", "emblem", "subtitle", "attributes".

"attributes" looks like a dictionary, so we'll need to document the settings it has as well.

[Michi Henning (michihenning)]

OK, turns out that these were actually documented. I expected to see something in the tutorial, but it's actually documented in detail in the CategoryRenderer doc.

I've added mascot-fallback and emblem-fallback.

Saviq, can you please check the doc for CategoryRenderer and let me know whether the field names I used are OK?

[James Henstridge (jamesh)]

Currently "art" can either be a string giving the field holding the art URI, or a dictionary with "field" and "aspect-ratio" keys. Perhaps it would make sense to handle fallbacks in this second form as a third key?

[Michał Sawicz (saviq)]

Yeah, just commented to the same note on the MP.

[Launchpad Janitor (janitor)]

This bug was fixed in the package unity8 - 8.10+15.10.20150618-0ubuntu1

---------------
unity8 (8.10+15.10.20150618-0ubuntu1) wily; urgency=medium

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[Michi Henning (michihenning)]

The thumbnailer cannot remove support for fallback images until after all the scopes and apps that depend on it have been updated. We are working on that.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.