v0.77.0: Double-page spreads, joined

Spreads that a source served as two pages can be read as one, and one page of a pair can be brought into frame.
Both began as pull requests from @Squeaks72 (#229,
#232, #261); the
spread detector is theirs. Thank you.

Double-page spreads, joined

• Join split double pages (#229, from @Squeaks72), in Reader
  settings and Profile → Settings → Reading. It is off until you turn it on. Some sources serve a double-page
  spread as two ordinary pages. In Paged mode the reader then shows the two as the spread, on one slide with the halves
  touching, in single page and Double spread alike.

  • The halves sit the way the picture runs, on the side the server found, whatever your reading direction.
  • The page before a spread gets a slide of its own, so the pairs after it stay as they were drawn. A chapter can open
    on a spread.
  • On a phone held upright, Wide pages works as it does for a spread scanned in one piece. Whole shows it across
    the screen, Split shows its two pages one after the other, and Rotate turns it on its side.
  • Only a joined spread loses the gap down the middle. Every other pair keeps its gutter.
  • The pages themselves never change: the counter, your progress, OPDS and your trackers still count two.

• Found in the background, once. The server compares the inner edge of each page with the next page's. It looks
  the first time someone with the setting on opens a chapter, one chapter at a time, and never while it answers the page
  list. A chapter opens at once, and its spreads join a moment later without moving the page you're on.

  • The answer is kept with the chapter, even when nothing was found or the file could not be read, so no chapter is
    looked at twice. A replaced file is looked at again.
  • A chapter downloaded after its spreads were found joins them offline too.

• Checked against this server's own library first. As first written, the detector joined separate pages far more
  often than it found spreads. In a sample of 375 chapters, 12 of its 80 joins were real spreads. Two facing pages whose
  borders line up (a black bleed down both inner edges, or a white gutter crossed by panel borders at the same heights)
  match as well as a real seam. Four tests now come after the match:

  • the same texture on both sides of the cut;
  • the small steps down the edge lining up, not only the bands;
  • no other page of the chapter fitting either edge as well;
  • the outermost columns of both pages being the same kind of thing.

  On the first sample it now makes the 12 real joins and no others. On a second sample of 410 chapters, 16 of its 17
  joins were real, and the one that was not led to the last test. On a third sample of 380 chapters, which it was never
  tuned on, 14 of its 16 joins were real; the other 2 are facing pages whose drawings run to the seam on panels that
  line up. No sample had a join in a webtoon chapter.

One page of a pair in frame

• Z (#261, from @Squeaks72) brings the first page of the pair on
  screen into frame, in Double spread or on a joined spread. The arrows then step to the other page before they turn,
  and Z again gives both back. A small squared key at the bottom names the page and gives both back too.
  • Z is an action like the others under Keys and controller: it can be rebound, Y does it on a controller, and the
    key list shows it.
• Tap a page of a pair to see it alone (#232, from @Squeaks72),
  a setting for this device. It is off until you turn it on. On a slide of two pages, a tap on one of them fills the
  screen with it in place of what its tap zone does. Turning toward the other page then shows that one.
  • Taps beside the pages still do what Tap zones says.
  • Off, every tap works as before, and the middle of the screen shows the controls.

Fixed

• Crop page borders on a pair read right to left trimmed the inner edges of the two pages and left their outer
  margins. It now trims the outer margins and keeps the gutter, as it always did left to right.

Upgrading

• Database: one new column, lib_books.spreads, empty until a chapter is looked at. Additive: v0.76.x ignores it.
• API: GET /api/books/:id/pages?spreads=1 adds join to the pages of a spread. The x-spreads header says
  whether the chapter has been looked at yet. Without the parameter nothing changes. See docs/api.md.

Uchiyomi Desktop (beta): downloads

Uchiyomi as a program on your own computer, for Windows and Mac. On first launch it asks how you want to
use it: on this computer (the whole app, with the library in a folder on your PC and no Docker or
server to run) or connected to your own Uchiyomi server (a window onto the server you already run).

Your computer	Download
Windows (x64)	Uchiyomi-Setup-0.77.0.exe
Mac with Apple silicon (M1 or newer)	Uchiyomi-0.77.0-arm64.dmg
Mac with an Intel processor	Uchiyomi-0.77.0-x64.dmg

Only those three are for you: the .zip, .blockmap and latest*.yml files are what the app's own updater
reads. The same installers are also here under names without a version (Uchiyomi-Setup.exe,
Uchiyomi-mac-arm64.dmg, Uchiyomi-mac-x64.dmg), which always lead to the newest release.

The app is not signed yet, so the first launch takes one extra step:

• Windows: "Windows protected your PC" appears once. Choose More info, then Run anyway. A PC
  with Smart App Control turned on blocks unsigned apps with no way past it; use the Docker install there.
• macOS: open the dmg and drag Uchiyomi to Applications. The first time you open it, macOS refuses;
  go to System Settings → Privacy & Security and choose Open Anyway.

Windows installs updates by itself. A Mac cannot update an unsigned app, so there a new version is a new
download; the menu-bar icon and Admin → Health say when one is out.

Step by step, with pictures -- which file, the first launch on each system, the two ways to use it, adding
sources, updates, backups, where files live and uninstalling:
the desktop guide.