Fonts getting corrupted in x11drv
wine at troy.rollo.name
Thu May 25 01:49:04 CDT 2006
The attached sample program demonstrates a bug in font handling that can lead
to corrupted fonts. Compile with "winegcc -g sysfont.c -lgdi32 -lcomdlg32".
Run the resulting a.out, and you will see the letter "C" in the top left
corner of the window, rendered in the system font. Click anywhere in the
client area of the window and the letter will change its shape, even though
it is still using the stock SYSTEM_FONT.
The left click action creates a device context for the default printer and
immediately deletes it. As part of the deletion of that device context,
DeleteDC selects the stock SYSTEM_FONT into the device context. Since printer
device contexts insist on scalable fonts, the existing (bitmapped) GDI font
for the system font is unable to serve, so a new one is created, which ends
up being based on the Tahoma (TrueType) font. On the next paint loop, when
the test program calls SetFont it is the new, scalable font (based on Tahoma)
that is found.
The Tahoma font has different glyph codes to the System font, such that 'C' is
glyph code 36 in the System font and 38 in Tahoma. Accordingly, x11drv
identifies the glyph as not having been uploaded (it has uploaded glyph 36
before), and uploads it as glyph 38 based on its outline in Tahoma.
The problem gets worse later on because some glyphs in the glyphset have been
uploaded according to their "System" font positions (or in this case ,the
same character has been uploaded in its position in both fonts). Rendering a
character that uses the other glyph code results in the wrong character. You
can get a mix of Tahoma and System characters appearing on the screen with
the System characters displaying the shape of the wrong character.
Every fix I look at seems like a horrible hack. Perhaps find_in_cache should
only return bitmap fonts if the device can use them. If the caller then finds
there is no bitmap font that matches it can then look for scalable fonts in
Troy Rollo - wine at troy.rollo.name
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