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readium / webpub-manifest

📜 A JSON based Web Publication Manifest format used at the core of the Readium project
BSD 3-Clause "New" or "Revised" License
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page: center and spread: none #104

Open qnga opened 2 weeks ago

qnga commented 2 weeks ago

page: center has been more or less deprecated in EPUB for interesting reasons that apply to RWPM as well.

The discussion pointed out that page: center was more about the lack of spread than centering because all spreads are centered and fitted. In RWPM too I guess we use it mainly to convey the idea that the page must not be part of a spread, which is quite confusing. I think it would be better to have a better named property and to have a discussion about it at the same time as we think about #103.

HadrienGardeur commented 2 weeks ago

There's one key difference between the EPUB spec and RWPM though: we've moved away from providing controls over spreads to authors.

At best, we're offering the ability to indicate that a spread is meaningful now (#103) which is very different from what EPUB offers.

There are two main use cases for page: center:

For the second one, I would say that it's a counter-part to what we're discussing in #103.

mickael-menu commented 2 weeks ago

That makes me think that in FXL EPUB we're supposed to display the first resource on its own by default (centered or not), unless otherwise is specified explicitly. It's something we didn't handle properly in Swift before.

I don't think we have this behavior specified in RWPM? It's pretty critical as it breaks any book laid out expecting spreads. I couldn't find it either in the EPUB specification, it's just the default behavior of Apple Books and so expected by book author.

qnga commented 2 weeks ago

covers where you want to place something at the center of the screen

What does that mean? Reading apps will fit the content, in a way depending to user preference or not. And no matter what the fit preference is, too small content will be centered.

and page spreads as a single image where you want to use the entire screen

Sure. Epub recommends the use of spread: none for this and it's far clearer. Besides, you're right, as the counter-part of meaningfulSpread, I wonder if both properties should not be related in the model.

HadrienGardeur commented 2 weeks ago

I don't think we have this behavior specified in RWPM? It's pretty critical as it breaks any book laid out expecting spreads. I couldn't find it either in the EPUB specification, it's just the default behavior of Apple Books and so expected by book author.

This doesn't necessarily belong in the spec IMO. It could be handled by automatically adding page: center to the first resource if it's missing any page property.

Sure. Epub recommends the use of spread: none for this and it's far clearer. Besides, you're right, as the counter-part of meaningfulSpread, I wonder if both properties should not be related in the model.

I wouldn't call the spread controls in EPUB "clear". It gives the illusion of control to anyone reading the specification, while in practice reading systems and users will do whatever they want (which is fine). The only two values that make sense somehow are none (which can be aliased to page: "center" in RWPM) and both (which can be aliased to meaningfulSpread: true in RWPM).

Even with these values, the toolkits should still offer ways to override their default behaviour.

qnga commented 2 weeks ago

I think we agree on the use cases : spreads and fit are controlled by users. All we need in the manifest is a way to give information about the publication itself to offer meaningful (literally) spreads when the user wants spreads:

We might actually want an answer to question 1 even in no-spread mode if we want to disregard fit to keep a consistent scale between pages. Is that something we want to be able to do? It's hard to specify a data model without processing model.

mickael-menu commented 2 weeks ago

This doesn't necessarily belong in the spec IMO. It could be handled by automatically adding page: center to the first resource if it's missing any page property.

I agree that it is not necessarily part of the spec, but it's still useful to document it in the processing model, so that authors know what to expect for the rendering. It was missing from EPUB and I mistakenly didn't assume that the first resource should be displayed on its own when implementing it.