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Re: about contibuting to octave

From: xianghang liu
Subject: Re: about contibuting to octave
Date: Wed, 4 Mar 2009 17:22:56 +0800

On Wed, Mar 4, 2009 at 2:48 PM, Shai Ayal <address@hidden> wrote:
2009/3/4 xianghang liu <address@hidden>:
> On Wed, Mar 4, 2009 at 10:00 AM, Ben Abbott <address@hidden> wrote:
>> On Mar 3, 2009, at 2:52 PM, Michael Goffioul wrote:
>>> On Tue, Mar 3, 2009 at 6:51 PM, Shai Ayal <address@hidden> wrote:
>>>> I think this is a good idea -- this will decouple the text object from
>>>> the backend.
>>>> We will need to know what fonts gnuplot uses to get freetype to get us
>>>> gnuplot's font metrics?
>>>> I think we can get the standard postscript font metrics from similar
>>>> type1 fonts which freetype can use (I distributed a set of ps-similar
>>>> fonts with octplot)
>>> I guess gnuplot backend would use the back-up implementation.
>>> Or we could still use freetype, hoping that gnuplot will use the same
>>> metrics...
>>> Michael.
>> Gnuplot uses the GD library.
>>        http://en.wikipedia.org/wiki/GD_Graphics_Library
>>        http://www.libgd.org/Main_Page
>> After reading some hits via Google, it appears that this library can
>> calculate the bounding rectangle text without rendering it, and that gdlib
>> handles freetype, PS type 1 fonts, and truetype.
>>        http://my.php.net/gd
>>        imageftbbox — Give the bounding box of a text using fonts via
>> freetype2
>>        imagepsbbox — Give the bounding box of a text rectangle using
>> PostScript Type1 fonts
>>        imagettfbbox — Give the bounding box of a text using TrueType fonts
>> Ben
> So there are already 3 methods to get the extent property without dependency
> on backends:

Well none of them are implemented in octave yet ...

> use GD library
> use freetype
> back-up method if these libraries is absent or the font is non-standard

Since it seems that GD uses freetype also, I would go for freetype +
very simple backup.


In freetype, I found two functions
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?


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