Caolán McNamara
11 years ago
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5ed5bf4e52
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From 71077148d442b3bbfeefd9a572942946c6a95823 Mon Sep 17 00:00:00 2001
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From: Khaled Hosny <khaledhosny@eglug.org>
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Date: Wed, 30 Oct 2013 09:34:38 +0200
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Subject: [PATCH] fdo#70968: Incorrect rendering of Devanagari short 'i' vowel
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It seems that some Indic fonts assign 'mark' glyph class to combining
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spacing marks (spacing not non spacing) so my reliance on the glyph
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class to set the IS_DIACRITIC flags broke those fonts. This is a bandaid
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to get around the issue, plus some long rant! (at this rate, I'll be
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writing "The VCL haters handbook" pretty soon).
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Change-Id: I3ff892acf746d50182573f94e7e8c3c6f9464ae0
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---
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vcl/generic/glyphs/gcach_layout.cxx | 26 +++++++++++++++++++++-----
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vcl/source/gdi/sallayout.cxx | 21 +++++++++++++++++++++
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2 files changed, 42 insertions(+), 5 deletions(-)
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diff --git a/vcl/generic/glyphs/gcach_layout.cxx b/vcl/generic/glyphs/gcach_layout.cxx
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index 4673931..7a8bfc9 100644
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--- a/vcl/generic/glyphs/gcach_layout.cxx
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+++ b/vcl/generic/glyphs/gcach_layout.cxx
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@@ -456,20 +456,36 @@ bool HbLayoutEngine::layout(ServerFontLayout& rLayout, ImplLayoutArgs& rArgs)
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if (bInCluster)
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nGlyphFlags |= GlyphItem::IS_IN_CLUSTER;
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+ // The whole IS_DIACRITIC concept is a stupid hack that was
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+ // introduced ages ago to work around the utter brokenness of the
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+ // way justification adjustments are applied (the DXArray fiasco).
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+ // Since it is such a stupid hack, there is no sane way to directly
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+ // map to concepts of the "outside" world, so we do some rather
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+ // ugly hacks:
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+ // * If the font has a GDEF table, we check for glyphs with mark
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+ // glyph class which is sensible, except that some fonts
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+ // (fdo#70968) assign mark class to spacing marks (which is wrong
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+ // but usually harmless), so we try to sniff what HarfBuzz thinks
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+ // about this glyph by checking if it gives it a zero advance
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+ // width.
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+ // * If the font has no GDEF table, we just check if the glyph has
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+ // zero advance width, but this is stupid and can be wrong. A
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+ // better way would to check the character's Unicode combining
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+ // class, but unfortunately glyph gives combining marks the
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+ // cluster value of its base character, so nCharPos will be
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+ // pointing to the wrong character (but HarfBuzz might change
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+ // this in the future).
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bool bDiacritic = false;
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if (hb_ot_layout_has_glyph_classes(mpHbFace))
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{
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// the font has GDEF table
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- if (hb_ot_layout_get_glyph_class(mpHbFace, nGlyphIndex) == HB_OT_LAYOUT_GLYPH_CLASS_MARK)
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+ bool bMark = hb_ot_layout_get_glyph_class(mpHbFace, nGlyphIndex) == HB_OT_LAYOUT_GLYPH_CLASS_MARK;
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+ if (bMark && pHbPositions[i].x_advance == 0)
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bDiacritic = true;
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}
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else
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{
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// the font lacks GDEF table
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- // HACK: if the resolved glyph advance is zero assume it is a
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- // combining mark. The whole IS_DIACRITIC concept is a hack to
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- // fix the other hacks we use to second-guess glyph advances in
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- // ApplyDXArray and the likes and it needs to die
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if (pHbPositions[i].x_advance == 0)
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bDiacritic = true;
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}
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diff --git a/vcl/source/gdi/sallayout.cxx b/vcl/source/gdi/sallayout.cxx
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index f395936..450ec232 100644
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--- a/vcl/source/gdi/sallayout.cxx
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+++ b/vcl/source/gdi/sallayout.cxx
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@@ -1018,6 +1018,27 @@ void GenericSalLayout::AdjustLayout( ImplLayoutArgs& rArgs )
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// -----------------------------------------------------------------------
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+// This DXArray thing is one of the stupidest ideas I have ever seen (I've been
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+// told that it probably a one-to-one mapping of some Windows 3.1 API, which is
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+// telling). To justify a text string, Writer calls OutputDevice::GetTextArray()
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+// to get an array that maps input characters (not glyphs) to their absolute
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+// position, GetTextArray() in turn calls SalLayout::FillDXArray() to get an
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+// array of character widths that it converts to absolute positions.
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+//
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+// Writer would then apply justification adjustments to that array of absolute
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+// character positions and return to OutputDevice, which eventually calls
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+// ApplyDXArray(), which needs to extract the individual adjustments for each
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+// character to apply it to corresponding glyphs, and since that information is
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+// already lost it tries to do some heuristics to guess it again. Those
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+// heuristics often fail, and have always been a source of all sorts of weird
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+// text layout bugs, and instead of fixing the broken design a hack after hack
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+// have been applied on top of it, making it a complete mess that nobody
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+// understands.
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+//
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+// As you can see by now, this is utterly stupid, why Writer does not just send
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+// us directly the advance width transformations it wants to apply to each
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+// character instead of this whole mess?
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+
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void GenericSalLayout::ApplyDXArray( ImplLayoutArgs& rArgs )
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{
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if( m_GlyphItems.empty())
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--
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1.8.3.1
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