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win32: Grow glyph extents to account for ClearType

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Add extra pixel on each side of the glyph's black box returned by
GetGlyphOutlineW, to avoid clipping ClearType pixels.

From https://bugzilla.mozilla.org/show_bug.cgi?id=445087
This commit is contained in:
Jonathan Kew 2010-05-11 15:12:01 -04:00 • committed by Jeff Muizelaar
parent d65e8064c0
commit 35307fc66f
1 changed files with 13 additions and 0 deletions
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13
src/cairo-win32-font.c
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@ -979,6 +979,19 @@ _cairo_win32_scaled_font_init_glyph_metrics (cairo_win32_scaled_font_t *scaled_f
GGO_METRICS | GGO_GLYPH_INDEX,
&metrics, 0, NULL, &matrix) == GDI_ERROR) {
memset (&metrics, 0, sizeof (GLYPHMETRICS));
} else {
if (metrics.gmBlackBoxX > 0 && scaled_font->base.options.antialias != CAIRO_ANTIALIAS_NONE) {
/* The bounding box reported by Windows supposedly contains the glyph's "black" area;
* however, antialiasing (especially with ClearType) means that the actual image that
* needs to be rendered may "bleed" into the adjacent pixels, mainly on the right side.
* To avoid clipping the glyphs when drawn by _cairo_surface_fallback_show_glyphs,
* for example, or other code that uses glyph extents to determine the area to update,
* we add a pixel of "slop" to left side of the nominal "black" area returned by GDI,
* and two pixels to the right (as tests show some glyphs bleed into this column).
*/
metrics.gmptGlyphOrigin.x -= 1;
metrics.gmBlackBoxX += 3;
}
}
cairo_win32_scaled_font_done_font (&scaled_font->base);