[mythtv-commits] Ticket #12057: Improve legibility and display of CEA-608 captions.

[MythTV]

#12057: Improve legibility and display of CEA-608 captions.
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 Reporter:  faginbagin <mythtv@…>  |          Owner:  stichnot
     Type:  Patch - Feature        |         Status:  accepted
 Priority:  minor                  |      Milestone:  0.28
Component:  MythTV - Captions      |        Version:  Unspecified
 Severity:  medium                 |     Resolution:
 Keywords:                         |  Ticket locked:  0
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Comment (by faginbagin <mythtv@…>):

 I am attaching a new patch based on offline discussions with stichnot. The
 highlights:

 !SubtitleFormat has a new font cache, m_fullFontMap, which caches fonts
 based on the full set of attributes: family, cc708 attrs, zoom & stretch.

 SubtitleFormat::Load implements a default font sizing algorithm shared by
 all caption types. It chooses a better font.pixelSize by making a first
 guess, then adjusting using QFontMetrics' height and lineSpacing to choose
 a font.pixelSize that works for all but the most extreme fonts.

 The algorithm takes into account video aspect ratio for 708 and text
 captions, outline size and shadow offset, font stretch and left & right
 padding.

 If the resulting font metrics lead to a font width that exceeds a max
 width based on the above, it logs a warning. It does not try to make a
 third adjustment. I haven't found a test case that triggers that warning.

 SubtitleFormat::!GetFont depends on Load, to initialize a default font
 cached in m_fontMap. !GetFont then applies more transient changes, such as
 zoom, color, italics, etc. and caches the result in m_fullFontMap.

 To reduce the number of calls to SubtitleFormat::!GetFont,
 !FormattedText[Chunk|Line]::Calc methods that were const, aren't anymore
 and the SubtitleScreen::Calc method now take an optional mythfont
 argument.

 Fixed a memory leak in SubtitleFormat::!CreateProviderDefault.

 Fixed a problem where left padding was outside the safe area and, when
 using the Slim display profile, the padding would be clipped.  The root
 cause was due to padding being applied twice in
 FormattedTextSubtitle::Layout. I addressed it by adding a bool addPadding
 argument to FormattedTextLine::!CalcSize.

 Made sure captions are drawn after new ones are added. Don't just depend
 on bounding rectangle changes. Affects captions using Slim profile that
 happen to have the same bounding box as the preceding caption. Effect can
 be seen playing:
 http://ncamftp.wgbh.org/DTV/CEA%20test%20material/Iteration_1/CEAv1.2zero.trp
 Without this patch, no captions are displayed for slides 3, 4 and 11,
 because their bounding box is identical to the preceding caption.

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Ticket URL: <https://code.mythtv.org/trac/ticket/12057#comment:7>
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