[Icons] Transparent app icon backgrounds look bad

unity8 waiting for design -> incomplete

Transparent backgrounds should be avoided for application icons cause the result looks very awkward once the Ubuntu shape and the shadow are applied.
Please try to design something consistent with the core app icons (our icon guidelines can help).

I agree authors SHOULDN'T use transparent backgrounds for icons.

But they currently CAN. And what should we do in that case?

I'm proposing that we default to a white (or black) background for them, rather then actually rendering it as transparent. But I don't care what the solution is, as long as it's consistent. Currently, we are inconsistently rendering the icon.

Looks like the presentation is now consistently transparent.

So that's good, sorta. I'm now going to change this bug to be about how transparent backgrounds for icons looks terrible.

I've proposed the attached branch to fix this.

I've added a task for ubuntu-system-settings, because I just remembered that it also displays app icons: in Storage, App Permissions, and Notifications.

But note that I'm still waiting on design input. Copied from the attached MP:

Paty when I asked about this branch: "Regarding the opinion on the colour choice for the icons BG, I pinged Mattheiu, who is the icon designer and he is gonna look into this and hopefully, comment on the bug ticket. I'm sorry I'm not able to help more on this. I think porcelain should work well, but I rather not make visual decisions... : P"

Applications icons are also rendered in Online Accounts, and in the trust prompt dialogs.

App icons are, or will be, also rendered by content-hub in its “Open With” dialog; by indicator-sound when a player is registered with Mpris; by url-dispatcher in its “Use App” dialog; and by any app that uses its own icon in a notification. (Presumably the notification cases can’t be fixed in notify-osd and indicator-messages themselves, because they don’t know whether the icon they receive is an app icon or something more specific.) That almost certainly still isn’t a complete list.

These “oh, we need to fix this bug here too, and here, and here” comments bolster my proposal in wontfixed bug 1363015: there should be a toolkit element for rendering an app’s icon in the current standard style. As long as every place that renders app icons has to include its own code for making a transparent background opaque, along with all their other details (icon location in click/snap packages, aspect ratio sanity-checking, rounded corners, relief/shadow, etc), then whenever the rendering of app icons changes, time will be wasted on multiple implementations and some of them will be forgotten or diverge accidentally.