[Freetype] ft_outline_ignore_dropouts is ignored

[Wenlin Institute]

Dear FreeTypers,

It looks like ft_outline_ignore_dropouts is ignored, and doesn't 
appear anywhere in the source except where it's defined in ftimage.h.

Also, in ftraster.c, dropOutControl is used in some conditionals, but 
it's only assigned the value 2 and there appears to be no way for it 
to have any other value (without editing ftraster.c), so it's 
effectively constant.

This matters in the rendering of Chinese horizontal strokes, as 
illustrated here:

   http://www.wenlin.com/ft_heng1.jpg

There are two problems. First, a "protruberent pixel" at the lower 
right corner of the first of the four strokes (and another one at the 
upper left corner). This can be fixed by changing the line 
"ras.dropOutControl = 2" to "ras.dropOutControl = 0" in 
Render_Glyph() in ftraster.c. Probably this ought to be the effect of 
ft_outline_ignore_dropouts. The result is the following:

   http://www.wenlin.com/ft_heng2.jpg

The second problem is, the four strokes are not equally thick. The 
coordinates of the outlines are such that the thickness should be 
uniform, and only the decorations (or serifs) at the left and right 
ends should differ. The uneven effect can be seen in the following 
Chinese characters:

   http://www.wenlin.com/ft_heng3.jpg

   http://www.wenlin.com/ft_heng4.jpg

For the thickness, it seems to make no difference what the value of 
dropOutControl is; ft_outline_single_pass and 
ft_outline_high_precision don't seem to matter either.

I'm directly filling in an FT_Outline and calling 
FT_Outline_Render(). The simplest (undecorated) outline is a 
rectangle. The left-side decoration is two straight lines. The 
right-side decoration (the bump) is one straight line and one curve 
(with two off-curve control points). Characters are rasterized one 
stroke at a time. The "undecorated" versions are used where strokes 
overlap.

I've tried stepping through the code in ftraster.c, but haven't 
managed yet to understand it. One thing that makes this harder is 
that I can't set breakpoints in ftraster.c (using OS X Project 
Builder, which is a shell around the GNU compiler/debugger); maybe 
the reason is that the project only contains raster.c, which has the 
line

#include "ftraster.c"

Has anyone else found this to be a problem? IDE's may not be good at 
handling this kind of code, where #include is used for .c rather than 
.h files.

Tom Bishop

--

Wenlin Institute, Inc.        Software for Learning Chinese
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Telephone: 1-877-4-WENLIN (1-877-493-6546)