Question about Calibre font subsetting

GrannyGrump · 12-22-2014, 05:41 AM

I have a custom font that exists entirely in the "Private Use Area" (Symbol Character Set). None of these are mapped to any character except in the Private Use Area.

When I used Calibre to subset the font (embedded in an epub), it deleted the entire font. In point of fact, at least 20 of these characters are used in the book text. Note that in the epub, I entered these characters in decimal: &#xnnnn;.

Is this because the font is mapped only to non-standard characters, or is there something else going on that I should search for?

kovidgoyal · 12-22-2014, 06:29 AM

Subsetting works by using the CMAP table (of type BMP) in the font, it maps unicode character codes from the Basic Multilingual Plane (BMP) to glyphs. If your font does not use a BMP type CMAP table to map unicode characters codes to glyphs then it wont be subset correctly.

IIRC BMP tables dont cover the private use area of unicode, so I doubt subsetting will work for such a font.

GrannyGrump · 12-23-2014, 12:07 AM

Thanks, Kovid, for the speedy reply. I expected it was something like that.

I will have to do it manually (it is a small font, no huhu!)

12-22-2014, 05:41 AM	#1
GrannyGrump Obsessively Dedicated... Posts: 3,200 Karma: 34977896 Join Date: May 2011 Location: JAPAN (US expatriate) Device: Sony PRS-T2, ADE on PC	Question about Calibre font subsetting I have a custom font that exists entirely in the "Private Use Area" (Symbol Character Set). None of these are mapped to any character except in the Private Use Area. When I used Calibre to subset the font (embedded in an epub), it deleted the entire font. In point of fact, at least 20 of these characters are used in the book text. Note that in the epub, I entered these characters in decimal: &#xnnnn;. Is this because the font is mapped only to non-standard characters, or is there something else going on that I should search for?

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12-22-2014, 06:29 AM	#2
kovidgoyal creator of calibre Posts: 43,850 Karma: 22666666 Join Date: Oct 2006 Location: Mumbai, India Device: Various	Subsetting works by using the CMAP table (of type BMP) in the font, it maps unicode character codes from the Basic Multilingual Plane (BMP) to glyphs. If your font does not use a BMP type CMAP table to map unicode characters codes to glyphs then it wont be subset correctly. IIRC BMP tables dont cover the private use area of unicode, so I doubt subsetting will work for such a font.

12-23-2014, 12:07 AM	#3
GrannyGrump Obsessively Dedicated... Posts: 3,200 Karma: 34977896 Join Date: May 2011 Location: JAPAN (US expatriate) Device: Sony PRS-T2, ADE on PC	Thanks, Kovid, for the speedy reply. I expected it was something like that. I will have to do it manually (it is a small font, no huhu!)