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* src/haiku_font_support.cc (BFont_char_bounds): Fix bearings.

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This commit is contained in:
Po Lu 2022-01-03 13:57:13 +00:00
parent c7768382cc
commit ab5ee3e29e
1 changed files with 25 additions and 6 deletions
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31
src/haiku_font_support.cc
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@ -126,9 +126,28 @@ BFont_have_char_block (void *font, int32_t beg, int32_t end)
return ft->IncludesBlock (beg, end);
}
/* Compute bounds for MB_STR, a character in multibyte encoding,
used with font. The width (in pixels) is returned in ADVANCE,
the left bearing in LB, and the right bearing in RB. */
/* Compute bounds for MB_STR, a character in multibyte encoding, used
with FONT. The distance to move rightwards before reaching to the
next character's left escapement boundary is returned in ADVANCE,
the left bearing in LB, and the right bearing in RB.
The left bearing is the amount of pixels from the left escapement
boundary (origin) to the left-most pixel that constitutes the glyph
corresponding to mb_str, and RB is the amount of pixels from the
origin to the right-most pixel constituting the glyph.
Both the left and right bearings are positive values measured
towards the right, which means that the left bearing will only be
negative if the left-most pixel is to the left of the origin.
The bearing values correspond to X11 XCharStruct semantics, which
is what Emacs code operates on. Haiku itself uses a slightly
different scheme, where the "left edge" is the distance from the
origin to the left-most pixel, where leftwards is negative and
rightwards is positive, and the "right edge" is the distance (where
leftwards is similarly negative) between the right-most pixel and
the right escapement boundary, which is the left escapement
boundary plus the advance. */
void
BFont_char_bounds (void *font, const char *mb_str, int *advance,
int *lb, int *rb)
@ -140,9 +159,9 @@ BFont_char_bounds (void *font, const char *mb_str, int *advance,
ft->GetEdges (mb_str, 1, &edge_info);
ft->GetEscapements (mb_str, 1, &escapement);
*advance = std::lrint (escapement * size);
*lb = std::lrint (edge_info.left * size);
*rb = *advance + std::lrint (edge_info.right * size);
*advance = std::ceil (escapement * size);
*lb = std::ceil (edge_info.left * size);
*rb = *advance + std::ceil (edge_info.right * size);
}
/* The same, but for a variable amount of chars. */