Does anyone know how the line spacing set via the slider on the font menu relates to the line-height CSS directive, if at all?
If I set the line spacing to minimum on the sider, readingLineHeight=1.3 is set in the device's configuration file. So I thought this would mean the same thing as if I had set line-height:1.3 in the CSS.
But it seems Kobo's readingLineHeight and the CSS line-height value only correspond when font-size:medium is active in the book's CSS. If I have the main text set to font-size:xx-large, then the lines overlap with the slider at minimum (i.e. line-height is less than 1.0), and if I have it set to font-size:x-small then the lines are about double spaced.
However if I set line-height:1.3 in the books CSS then the line height remains proportional regardless of the font-size, the lines are never overlapping or double-spaced.
So this means that the line spacing set via the font menu slider is not changing the line-height in the same way as setting it in the CSS. Hence my question: how to they relate?
Personally I find the minimum slider-set line spacing (readingLineHeight=1.3) comfortable if the book is using a medium font-size, but some books, for reasons I cannot figure out, use font-size:small or x-small for the main text, which causes the actual line spacing to appear proportionally much larger.
This also means that scaling up all the font-size directives in a book's CSS (medium to large, small to medium, etc.) would make the minimum slider-set line spacing much closer, which would probably be more useful (because the slider-set range would be shifted, it could be set near the middle of the range with room to adjust both ways, instead of always at the minimum).
Edit:
The cause of the problem was exactly as tshering speculated in post #2. See post #31 for a firmware patch that fixes the problem.