InDesign to EPUB to Thorium Reader — bug in TR

[James Gifford—NitroPress]

Another slightly aside issue that anyone who exports to EPUB should know.

I, and many others, prefer Thorium Reader as a clean, standards-driven, nicely "vanilla" reader for EPUB.docs. If it's right in TR, it's good to go.

Except that there's a noxious bug of long standing, which I recently tripped over. Put briefly, Thorium uses a very aggressive font-size 'regularizing' algorithm, designed to get around bad EPUB code using fixed font sizing (px, pt, mm etc.) One side effect is that on some documents, it will force all styles to 1em/rem. The size definition of the style is ignored. The problem has been reported (in GitHub) for almost two years; each ticket is noted and closed. The programmer responsible more or less says he can't find a way to apply the font fix AND respect all author stylesheets, so the issue persists.

The punchline here: the problem seems to apply mostly, if not only to EPUB exported from ID.

I expended quite a bit of effort trying to fix/cure the problem without success and before discovering it was inherent in the reader. It also applies to the browser plug-in EPUBreader, my other go-to proofing tool, which I believe borrows the root Readium code. However, the Calibre, Sigil and Ice Cream readers all present EPUBs (from ID) with size styles respected, so it is a solvable problem... someday.

Just a heads up until the EDRlab folks figure out how to please both masters.

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