[ft] Glitchy stroker output

[Stephan T. Lavavej]

Hi,

 

I've noticed that strokers can produce glitchy output, especially when thicker borders are requested.

 

Here's a self-contained repro: http://stl.nuwen.net/pub/freetype/

 

I compiled it with my MinGW distribution at http://nuwen.net/mingw.html , containing FreeType 2.3.7, with the command line "g++ -Wall -Wextra repro.cc -o repro.exe -lfreetype".

 

zeroes_three.ttf is the freely available Zeroes Three font from http://larabiefonts.com .

 

repro.cc is controlled by the first three lines of main(), which specify the font filename, the nominal pixel height, and the real 26.6 border radius to render.

 

With a nominal pixel height of 24, here are examples of output for 2, 4, and 6 pixel borders:

 

http://stl.nuwen.net/pub/freetype/output2.png

http://stl.nuwen.net/pub/freetype/output4.png

http://stl.nuwen.net/pub/freetype/output6.png

 

output2.png looks basically good, although there are some minor glitches that I'll point out below.  (These glitches are actually the ones that most concern me, as this border radius is the one that I'll be using in practice.)  Ignore the weird box between ']' and '_'; that says "LARABIE FONTS".

 

output4.png contains significant glitches.  It appears that they always occur on the right sides of glyphs, never the left sides.  For example, 'S' is basically rotationally symmetric, and its left side is perfect, but its right side is glitchy.

 

output6.png contains massive glitches.  Interestingly, some of the borders have detached from their core glyphs, for example '.', '!', and '?'.

 

Going back to output2.png, minor glitches are evident after looking at the larger borders.  For example, the right edges of ')' and '=', and the upper-right corners of 'V' and 'y' suffer glitches.

 

Am I doing something wrong, or is this a bug in FreeType?

 

Thanks,

Stephan T. Lavavej