bugThe FreeType Project - Bugs: bug #20476, linearHoriAdvance is snapped to...


bug #20476: linearHoriAdvance is snapped to some integer value with monospaced fonts

Submitted by:  None
Submitted on:  Fri 13 Jul 2007 03:05:52 PM UTC  
Severity:  3 - Normal Item Group:  Incorrect behaviour
Status:  Wont Fix Privacy:  Public
Assigned to:  David Turner <freetype> Open/Closed:  Closed
Planned Release:  None

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Fri 13 Jan 2017 07:29:39 AM UTC, comment #2:

To be more precise: It was a bug that the `linearHoriAdvance' values of proportional fonts were strictly proportional to the `char_height' (or `char_width') parameter of `FT_Set_Char_Size'.

This has been fixed meanwhile (already a few years ago, I no longer remember).

The `char_height' parameter gives a size in fractional points, not pixels. The resulting pixel size is always an integer value.

Werner LEMBERG <wl>
Project Administrator
Fri 13 Jan 2017 04:16:55 AM UTC, comment #1:

This is not a bug. The outlines are scaled and rendered properly without any rounding. The rounding of advances happens because you cannot render bitmaps at fractional pixels. Accounting for the accumulating rounding errors by adding/removing pixels won't work, because the font won't look fixed. It is what it is.

Alexei Podtelezhnikov <podtelez>
Project Member
Fri 13 Jul 2007 03:05:52 PM UTC, original submission:

In TT font Courier New (windows file cour.ttf) linearHoriAdvance, should be accurate and strictly proportional to the sub-pixel height you set. However, it is snapped to some value.

Font: cour.ttf from WinXP
Then you set:
FT_Set_Char_Size(face, 0, height, 72, 72);
where "heights" are:
7.02, 7.80, 8.58, 9.36, 10.14, 10.92, 11.70, 12.48,
13.26, 14.04, 14.82, 15.60
(in the corresponding 26.6 units of course)

It results in the following picture using linearHoriAdvance:
With any proportional font there's no such effect and the text width is proportional to the given height.



(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach Files:

Attached Files
file #13329:  12cour.png added by None (38KiB - image/png)


Depends on the following items: None found

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    Follow 4 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    Fri 13 Jan 2017 04:16:55 AM UTC podtelez StatusNone => Wont Fix
        Open/ClosedOpen => Closed
    Fri 13 Jul 2007 09:23:41 PM UTC wl Assigned toNone => freetype
    Fri 13 Jul 2007 03:05:53 PM UTC None Attached File- => Added 12cour.png, #13329

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