about contibuting to octave

[xianghang liu]

On Wed, Mar 4, 2009 at 9:14 PM, Ben Abbott <bpabbott at mac.com> wrote:

>
> On Mar 4, 2009, at 5:09 AM, Michael Goffioul wrote:
>
>  On Wed, Mar 4, 2009 at 9:22 AM, xianghang liu <xianghangliu at gmail.com>
>> wrote:
>>
>>> In freetype, I found two functions
>>>
>>> FT_Outline_Get_BBox Compute the exact bounding box of an outline.
>>> FT_Outline_Get_CBox Return an outline's ‘control box’.
>>>
>>> After a rough glance at ftgl's bounding box computation, I think it use
>>> FT_Outline_Get_CBox to compute the box of each glyph and add them
>>> together
>>> to get the extent of the string. Shall we just follow the same method?
>>>
>>
>> AFAIK, depending on the font, the width of a string is not the same as
>> the sum of the width of all its characters. OTOH, I think you can assume
>> that the width of a string will always be <= than the sum of the width of
>> its characters. So adding the box of each glyph should give you a maximum
>> width anyway.
>>
>> Note that I'm not a font expert, so I might be wrong.
>>
>> Michael.
>>
>
> I'm uncertain about this as well. Does anyone following along know?
>
> I was under the impression that the spacing between characters depends upon
> the neighboring characters (however, I might be thinking of LaTeX, which I'd
> expect to have a more complicated scheme). If a string's extent is not the
> sum of is character's extents, then we will require something to calculate
> the extents of a string directly. Which is something that gdlib and ftgl
> provide for.
>
> In any event, I'm thrilled that xianghang has taken on this effort. From my
> perspective this represents the largest obstacle to improving the
> compatibility of the gnuplot backend.
>
> Ben



I found two methods to get the extent of text objects by freetype:

   - use *FT_Outline_Get_CBox* to get the bounding box of a single glyph and
   *FT_Get_Kerning* to get the kerning vector between two glyphs. This is
   the method used in FTGL and contained in *FTFontImpl::BBox*I.
   - in gdft.c of gd library source code, there is a function
*gdImageStringFTEx
   *and some similiar funcions. These functions implement another method to
   get bounding box from glyph metrics. These functions are what PHP function
   *imagettfbbox *use to get bounding box. Call to these functions can be
   found in PHP source code  \php-5.2.9\ext\gd\gd.c

 Xianghang Liu
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