Hello,
We have a strange rendering issue with freetype library that
is driving us to ask an opinion from you.
Our application is using two free true type fonts:
DejaVuSans.ttf and DejaVuSans-Bold.ttf, in monochrome bitmap way, with
horizontal alignment; the issue basically consists in the following: the
‘r’ character is being displayed in a higher position, on the
baseline.
Two different versions of freetype library are producing a
different result:
- a relative recent version of ft (2.4.6) is showing
the problem
- an older version of ft (2.3.9) is properly
displaying the character
I have made some debug and discovered the following:
- If I reduce the horizontal bearing Y parameter, the char
is properly aligned on the baseline
- the metrics are showing me that there is not difference on
the values that are managing the bitmap glyph, so it seems that the
horizontal bearing Y recovered from the font file, through the library are the
same. So, since the code base that is managing the application is the
same, I am wondering where the issue is.
I have created a prototype application that loads the font,
render them in a txt file with a specific char in the pixels that are full of
color (‘o’) and also prints out the metrics values. The code is in attachment. The final result
is that old version of freetype load the glyph in this way
....
OOO.
O...
O...
O...
O...
O...
bitmapGlyph->metrics:
bitmapGlyph->metrics.height 7
bitmapGlyph->metrics.horiAdvance 4
bitmapGlyph->metrics.horiBearingX 1
bitmapGlyph->metrics.horiBearingY 7
bitmapGlyph->metrics.vertAdvance 11
bitmapGlyph->metrics.vertBearingX -2
bitmapGlyph->metrics.vertBearingY 3
bitmapGlyph->metrics.width 4
while the new one:
OOO
O..
O..
O..
O..
O..
bitmapGlyph->metrics:
bitmapGlyph->metrics.height 7
bitmapGlyph->metrics.horiAdvance 4
bitmapGlyph->metrics.horiBearingX 1
bitmapGlyph->metrics.horiBearingY 7
bitmapGlyph->metrics.vertAdvance 11
bitmapGlyph->metrics.vertBearingX -2
bitmapGlyph->metrics.vertBearingY 3
bitmapGlyph->metrics.width 4
So I can see a difference on the bitmap, but since the font
file is the same, the code is the same, just the freetype libraries are
different.
I am wondering if there is another parameter or test that I
can do in order to understand what is going on; have you got any suggestions?
Thanks in advance for your consideration.
Mauro
