Option to manipulate xAvgCharWidth #1167
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[why] When we have a ttc and tweak the contained fonts we recalculate the total checksum after each tweak while we only need to tweak it after all changes (included fonts) have been tweaked. [how] Pull the total checksum recalculation out of the subfonts loop. Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>
[why] Some old applications seem to depend on obsolete xAvgCharWidth values to show two-cell glyphs correctly. Fontforge can only generate OS/2 tables version 4, but these applications need 2 or less. In fact they seem to not look up the version number, but rely on the value being like it always has been ;-) One example is Windows notepad, that takes the xAvgCharWidth as base for the cell size and draws the two-cell chars in a cell twice that size - without any regard to glyph width. [how] These issue seems to be encountered rather seldom and only with some obscure (grin) applications. There is also no good way to handle this automatically. So we add a command line option that allows the user to tweak the value after patched-font generation. The option is called `--xavgcharwidth`: * If not specified the behavior of the patcher does not change * If just given the xAvgCharWidth is copied over from the source * If a number is added that number is used as xAvgCharWidth * If the number added is zero we will calculate the old style xAvgCharWidth Fixes: #522 Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>
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Description
[why]
Some old applications seem to depend on obsolete
xAvgCharWidthvalues toshow two-cell glyphs correctly. Fontforge can only generate OS/2 tables
version 4, but these applications need 2 or less. In fact they seem to
not look up the version number, but rely on the value being like it
always has been ;-)
One example is Windows
notepad, that takes thexAvgCharWidthas base forthe cell size and draws the two-cell chars in a cell twice that size -
without any regard to glyph width.
[how]
These issue seems to be encountered rather seldom and only with some
obscure (grin) applications. There is also no good way to handle this
automatically. So we add a command line option that allows the user to
tweak the value after patched-font generation.
The option is called
--xavgcharwidth:xAvgCharWidthis copied over from the sourcexAvgCharWidthxAvgCharWidthFixes: #522
Requirements / Checklist
What does this Pull Request (PR) do?
Add possibility to manipulate the OS/2 table entry
xAvgCharWidth, whichfontforgedoes not allow to modify and always fills with 'modern' values.How should this be manually tested?
Any background context you can provide?
https://learn.microsoft.com/en-us/typography/opentype/spec/os2#xavgcharwidth
https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6OS2.html
fontforge/fontforge#4899
https://forum.glyphsapp.com/t/font-custom-parameters/1174
What are the relevant tickets (if any)?
Screenshots (if appropriate or helpful)