About MuPDF ePub renderer

[roger64]

Hi

I opened some ePubs using the MuPDF renderer. I employed the recent Frenzie patch which modifies the font-size to "50". This size fits globally and needs not to be changed for text display. Some days ago, with the latest OTA Koreader version, a new dpi setting for MuPDF font-size has been added.

The comments below do not pretend to be exhaustive but address some of the current points which could be improved.

Displaying text.

I would give it globally a 9 out of 10 mark. Most of the time, the display is very precise. The display is very pleasantly crisp and reacts well to boldness settings. Embedded fonts display is quite good.

I spotted some few defects.

1. No hyphenation (or I did not know how to make it work).
2. Mishandling of <br/> tags. These are displayed like empty paragraphs instead of linebreaks (the gap is much too wide). I tried to declare a value of 0.5em or 2px to br in CSS, but this was not taken into account.
3. Padding and blockquote properties seem to be ignored. If need be, user agent margin values provide a replacement for exemple for h2 titles.

Remark: to go well with MuPDF, your CSS font-size values should not be written in pixels but in em or % values.

Displaying images.

I would give it 5 out of 10. It is difficult to assess. It somewhat complements the Coolreader renderer. The main miss is that the MuPDF renderer does not seem to comply with relative values. At this time, MuPDF fails also to display svg wrappers (mostly used for covers). On the other hand, it can display real svg images while cre can't.

Raster images

Displayed to their original size. CSS relative values seem to be ignored. Pinching out expands the display to full page. This works consistently when the image is contained in its own page.

Pinching out may look a little haphazard when performed on the image. If this is so, do it on the adjacent full text page (which obliterates margins and fits text to page) and then come back to the image page. When the page contains just one line of text, the display can be frightening (just one letter page high...)
Boldness is better kept at minimum value when displaying an image.

Unhappily I did not find any way to improve the display of smaller images embedded within the text. They seem to be stuck to their original size, which can be disappointing.

svg images

Contrary to cre, MuPDF displays pure svg images. Relative values seem to be ignored. For now the display is much smaller than it should be.

Pinching out to expand the svg image works but provides a huge and useless display. This is due to the specificity of svg format which cannot work like raster. It's also tricky to trigger and looks like an hit and miss process.

Non displaying tables

Text from tables is displayed on a single column. Other columns are ignored.

Conclusion

Now, MuPDF can best be used for ePubs containing mostly text. We can also use it to display svg images. My first wishes would be to enable hyphenation and enable it to take into account relative values for images.

[Frenzie]

I'm afraid there isn't much that can be done about most of that. For some of the bigger issues you could try checking upstream at https://bugs.ghostscript.com/

The <br\> issue: https://bugs.ghostscript.com/show_bug.cgi?id=698351

Hyphenation: https://bugs.ghostscript.com/show_bug.cgi?id=697707

Image width: https://bugs.ghostscript.com/show_bug.cgi?id=695941

[roger64]

Originally Posted by Frenzie

I'm afraid there isn't much that can be done about most of that. For some of the bigger issues you could try checking upstream at https://bugs.ghostscript.com/

The <br\> issue: https://bugs.ghostscript.com/show_bug.cgi?id=698351

Hyphenation: https://bugs.ghostscript.com/show_bug.cgi?id=697707

Image width: https://bugs.ghostscript.com/show_bug.cgi?id=695941

Thank you for these links and for pointing the only way ahead.

I'll certainly do what I can to make change the current status of these bugs from "unconfirmed" to "confirmed". One step at a time...