[ros-dev] Greenville: The story of Freetype VS the windows rasterizer---

[Wierd Wierd]

Hey everybody- 

I seem to be consistantly running into troubles with
Freetype and Greenville.  I suspect the problem stems
from Freetype trying to render the glyph with too many
shades of grey, and I *SERIOUSLY NEED* somebody to fix
it.

Here is a more technical view of the situation, and
the problem:


The TrueType hinting system allows each pixel to be
subdivided into sub-units. There are 81 subunits per
pixel, in a 9x9 grid, with the center being the origin
point.  So, it looks something like this:

87654321012345678
7XXXXXXXXXXXXXXXX
6XXXXXXXXXXXXXXXX
5XXXXXXXXXXXXXXXX
4XXXXXXXXXXXXXXXX
3XXXXXXXXXXXXXXXX
2XXXXXXXXXXXXXXXX
1XXXXXXXXXXXXXXXX
0XXXXXXXXXXXXXXXX
1XXXXXXXXXXXXXXXX
2XXXXXXXXXXXXXXXX
3XXXXXXXXXXXXXXXX
4XXXXXXXXXXXXXXXX
5XXXXXXXXXXXXXXXX
6XXXXXXXXXXXXXXXX
7XXXXXXXXXXXXXXXX
8XXXXXXXXXXXXXXXX

That represents the total number of subunits, and
their coordinate placements within 1 pixel.  

The windows rasterizer determines the 'shade' the
pixel will get, based on % of coverage this pixel gets
from the outline, as does freetype.  The problem shows
up, because The windows type rasterizer only renders
16 shades, including Black and White, while the
Freetype one renders 256 shades.

There are only 81 units, however.

What does this mean? It means that under freetype as
it currently stands, if even *ONE* pixel subunit is
covered by an outline, it will render as a shade of
grey--- While the exact same pixel, with the windows
rasterizer, will render as 'white' instead.

This is because "white" is 1/256th coverage, and there
are only 81 subunits-- Essentially meaning that in
order to get 'white' out of freetype, the pixel cannot
be touched *AT ALL* by the glyph outline.

On the windows rasterizer, there are only 16 shades of
grey, so up to 1/16th of the area can be covered, and
still rendered as 'white'-- or 5 subunits covered.

This is why the windows rasterizer produces crisper
images than Freetype.

I don't know how to fix this behavior in Freetype, and
*SERIOUSLY* need said behavior changed, As soon as
possible.

Thank you.



		
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