[mythtv-commits] Ticket #3584: Don't pre-cache glyphs for non-displayable control chars

[MythTV]

#3584: Don't pre-cache glyphs for non-displayable control chars
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 Reporter:  sphery <mtdean at thirdcontact.com>  |       Owner:  ijr    
     Type:  patch                             |      Status:  new    
 Priority:  minor                             |   Milestone:  unknown
Component:  mythtv                            |     Version:  head   
 Severity:  medium                            |  
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 The attached patch changes the OSD to skip pre-caching of glyphs for the
 C0 (0-31) and C1 (127-159) control characters.  Since they are non-
 displayable characters, they shouldn't have any glyphs, so we're just
 caching 65 copies of the "no glyph" rectangle for each font.

 Upon playback startup, my machine creates 120 fonts and pre-caches the
 glyphs for the first 256 characters of each, regardless of whether they're
 already cached elsewhere.  Therefore, skipping 65 non-displayable glyphs
 for 120 fonts saves caching 7800 glyphs that likely won't be used.

 If the glyph is later requested, it will be cached at that point, so this
 won't create issues if any of these characters are actually used.
 However, after applying this patch to my working copy, the only glyph that
 was ever requested from this range (in almost 2 weeks of admittedly
 8859-1-centric use with captions enabled) is that for U+000a (linefeed).
 While we could just pre-cache that glyph, it's not used in all programs,
 so it makes more sense to me to let it be cached upon request.

 While the fact that these characters (or at least the C1 control
 characters) are non-displayable may be specific to 8859-n encodings, the
 idea of pre-caching the first 256 glyphs from the font is probably equally
 8859-n (or possibly even 8859-1) specific.  And, since the glyphs will be
 cached on request, it doesn't hurt to skip pre-caching them.  As a matter
 of fact, chances are that if one of these glyphs is requested, it will
 only be for the font that's actually being used (i.e. the VBI CC font or
 the OSD font or ...) rather than caching the glyph for each of the 120
 fonts that may be used during playback.

 Note that my machine was set to use FreeSans for /all/ caption fonts,
 including the ATSC mono/serif/sans in regular/italic/bold/oblique and was
 using the Retro-OSD theme.  Therefore, only 3 unique fonts, Bitstream Vera
 Sans (Bold), Bitstream Vera Sans (Roman), and FreeSans (Medium), were
 actually used even though 120 were created (although some may have been
 different sizes).

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Ticket URL: <http://svn.mythtv.org/trac/ticket/3584>
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