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; * src/composite.h: Improve comments for LGSTRING and LGLYPH.

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This commit is contained in:
Eli Zaretskii 2021-06-02 17:50:57 +03:00
parent bef00aa137
commit f7d4bbceee
1 changed files with 17 additions and 0 deletions
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17
src/composite.h
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@ -243,6 +243,11 @@ composition_valid_p (ptrdiff_t start, ptrdiff_t end, Lisp_Object prop)
/* Macros for lispy glyph-string. This is completely different from
struct glyph_string. */
/* LGSTRING is a string of font glyphs, LGLYPHs. It is represented as
a Lisp vector, with components shown below. Once LGSTRING was
processed by a shaping engine, it holds font glyphs for one or more
grapheme clusters. */
#define LGSTRING_HEADER(lgs) AREF (lgs, 0)
#define LGSTRING_SET_HEADER(lgs, header) ASET (lgs, 0, header)
@ -256,6 +261,10 @@ composition_valid_p (ptrdiff_t start, ptrdiff_t end, Lisp_Object prop)
#define LGSTRING_ID(lgs) AREF (lgs, 1)
#define LGSTRING_SET_ID(lgs, id) ASET (lgs, 1, id)
/* LGSTRING_GLYPH_LEN is the maximum number of LGLYPHs that the
LGSTRING can hold. This is NOT the actual number of valid LGLYPHs;
to find the latter, walk the glyphs returned by LGSTRING_GLYPH
until the first one that is nil. */
#define LGSTRING_GLYPH_LEN(lgs) (ASIZE ((lgs)) - 2)
#define LGSTRING_GLYPH(lgs, idx) AREF ((lgs), (idx) + 2)
#define LGSTRING_SET_GLYPH(lgs, idx, val) ASET ((lgs), (idx) + 2, (val))
@ -275,6 +284,14 @@ enum lglyph_indices
LGLYPH_SIZE
};
/* Each LGLYPH is a single font glyph, whose font code is in
LGLYPH_CODE.
LGLYPH_FROM and LGLYPH_TO are indices into LGSTRING; all the
LGLYPHs that share the same values of LGLYPH_FROM and LGLYPH_TO
belong to the same grapheme cluster.
LGLYPH_CHAR is one of the characters, usually the first one, that
contributed to the glyph (since there isn't a 1:1 correspondence
between composed characters and the font glyphs). */
#define LGLYPH_NEW() make_nil_vector (LGLYPH_SIZE)
#define LGLYPH_FROM(g) XFIXNUM (AREF ((g), LGLYPH_IX_FROM))
#define LGLYPH_TO(g) XFIXNUM (AREF ((g), LGLYPH_IX_TO))