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glamor: Work around libXfont when it fails to use defaultChar

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GetGlyphs is supposed to always return the full list of characters
when there is a default character available. However, if an
application opens a 16-bit two dimensional font and then draws with
8-bit requests, the bitmapGetGlyphs function in libXfont versions up
through 1.4.7 will return zero glyphs if there is no 0th row.

While this is a bug in libXfont and should be fixed there, it's easy
to protect glamor from it by simply falling through to the case that
handles GetGlyphs failures for fonts without a default character.

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
This commit is contained in:
Keith Packard 2014-04-25 20:25:56 -07:00 committed by Eric Anholt
parent 91767a3287
commit 4711182033
1 changed files with 24 additions and 10 deletions
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34
glamor/glamor_text.c
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@ -37,6 +37,7 @@ glamor_get_glyphs(FontPtr font, glamor_font_t *glamor_font,
unsigned long nglyphs;
FontEncoding encoding;
int char_step;
int c;
if (sixteen) {
char_step = 2;
@ -49,7 +50,7 @@ glamor_get_glyphs(FontPtr font, glamor_font_t *glamor_font,
encoding = Linear8Bit;
}
/* If the font has a default character, then we don't have to
/* If the font has a default character, then we shouldn't have to
* worry about missing glyphs, so just get the whole string all at
* once. Otherwise, we have to fetch chars one at a time to notice
* missing ones.
@ -57,15 +58,28 @@ glamor_get_glyphs(FontPtr font, glamor_font_t *glamor_font,
if (glamor_font->default_char) {
GetGlyphs(font, (unsigned long) count, (unsigned char *) chars,
encoding, &nglyphs, charinfo);
} else {
int c;
for (c = 0; c < count; c++) {
GetGlyphs(font, 1, (unsigned char *) chars,
encoding, &nglyphs, &charinfo[c]);
if (!nglyphs)
charinfo[c] = NULL;
chars += char_step;
}
/* Make sure it worked. There's a bug in libXfont through
* version 1.4.7 which would cause it to fail when the font is
* a 2D font without a first row, and the application sends a
* 1-d request. In this case, libXfont would return zero
* glyphs, even when the font had a default character.
*
* It's easy enough for us to work around that bug here by
* simply checking the returned nglyphs and falling through to
* the one-at-a-time code below. Not doing this check would
* result in uninitialized memory accesses in the rendering code.
*/
if (nglyphs == count)
return;
}
for (c = 0; c < count; c++) {
GetGlyphs(font, 1, (unsigned char *) chars,
encoding, &nglyphs, &charinfo[c]);
if (!nglyphs)
charinfo[c] = NULL;
chars += char_step;
}
}