On Thursday, June 28, 2007 7:45 PM [GMT+1=CET],
Stephan Assmus <superstippi <at> gmx.de> wrote:
> So basically, I get to chose between blurry text or a couple of
> whitespaces that are one pixel too large or too small? I think I go
> with the wrong whitespaces.  I don't understand why rounding
> errors would be a problem. Basically, it is a problem of "matching"
> the tweaked layout to the theoretically perfect layout. I don't see a
> reason why the final remaining error would not be less than one
> pixel. Maybe I am missing something, but I can't see it just now.
Assume that you output a glyph for the letter "i" which is exactly
2.4 pixel wide. If you grid-fit it using the hinter, you'd probably
get a 2 pixel wide shape. Assume that a space measure 4 pixels.
Now, imagine you display "iiiiiiiiii" (ten times the "i" glyph).
This would produce a word which occupies 20 pixels on screen, yet
the typographic position should move by 24 pixels. You end up adding
4 pixels to the following space, which doubles its size. This will
look strange on the screen.
Worse, if the "i" glyph measures 2.6 pixels, and the hinter decides
to grid-fit it to occupy 3 pixels, you'll occupy 30 pixels on screen
whereas the typographic position only advanced by 26 pixels. This
time, you get a -4 pixel error which completely eats away the space.
Another approach would be to position the "i" glyphs by rounding
their typographic position, which would lead us to use the following
x coordinates in the 2.4 pixel wide case :
x = 0 ----> 0 error = 0 width=2
x = 2.4 --> 2 error = -0.4 width=3
x = 4.8 --> 5 error = +0.2 width=2
x = 7.2 --> 7 error = -0.2 width=3
x = 9.6 --> 10 error = +0.4 width=2
The result is ugly :
.*.*..*.*..*
............
.*.*..*.*..*
.*.*..*.*..*
.*.*..*.*..*
.*.*..*.*..*
You get the idea... The "i" glyphs appear at irregular intervals.
These considerations made me choose the blurry output.
Pierre
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