https://bugs.documentfoundation.org/show_bug.cgi?id=170596

            Bug ID: 170596
           Summary: Do not allow different font substitutions on different
                    media
           Product: LibreOffice
           Version: unspecified
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: medium
         Component: LibreOffice
          Assignee: [email protected]
          Reporter: [email protected]

Currently, it's possible to have different output of substituted glyphs on
different media: on screen vs. on print vs. in exported PDF.

This is because we have per-output-device font lists (filtered by support
claimed by fonts?); and for missing fonts (or missing glyphs), font
substitution triggers individually for each media.

But that is completely wrong. The "support" claimed by font, in today's world,
will not prevent *any* font to be rendered on *any* device. The "support" is
rather a design choice, indicating that the font was created with this-or-that
device in mind, so it's optimized for this medium, and looks best there, but
not elsewhere. So this information could be ~reasonably taken into account
*when we search for substitution* - exactly once (we could tweak the algorithm,
if supported by the underlying technology like fontconfig, to prefer e.g.
printer-ready fonts; or fonts without license restrictions; or any other things
that may be present in font metadata).

But once we have chosen that this character uses this glyph of this font, when
we applied the character properties to it - since this moment, *exactly this
glyph of this font* must be used in all output: on screen, to any printer, to
PDF, etc. This is called WYSIWYG, and our current behavior is simply breaking
this principle.

It is especially bad, since the substitution is mostly out of user control
(there is a way to define font substitution rules for missing fonts, which is
for advanced users; but there is no way to control "missing glyph"
substitution).

The immediate reason to file this bug was a discussion around bug 170590; but I
remember seeing other similar-looking bugs in the tracker.

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