Re: How do I get X, Y pos and PangoLogAttr of each glyph in a rendered string?

[Behdad Esfahbod <behdad behdad org>]

On 04/20/11 09:14, Alex Kerr wrote:
> Thanks very much for the help.
> 
>> You definitely can do it with glyphs...
> 
> OK, cool, so how - i.e. which APIs and how do I tie them together please?
> That's what's got me stuck!
> 
>> ...but is that really what you want? There's simpler API in pango to do that
> per cluster.
> 
> I'm not sure :) What's the definition of a cluster (and for that matter a
> glyph) ? I can't find this in the docs.

A glyph is a single shape from the font.  A cluster is a mapping between one
or more consecutive Unicode characters in the input text and one or more
consecutive glyphs in the glyph array that collectively correspond to eachother.


> And what's the simpler API you're referring to?

The PangoLayoutIter API, which has next_cluster().

If you want more direct access, check pango_layout_get_line(), and note that
PangoLayoutRun is the same as PangoGlyphItem.  Then check PangoGlyphItemIter,
or just do whatever you want to the glyph-item.


> Thanks for the Python code. I can't actually use Python (don't program in it,
> don't have it installed) but will read it as pseudocode and attempt similar in C!

The code illustrates which API calls you can use.

behdad


> Cheers
> Alex
> 
>  On 20/04/2011 06:11, Behdad Esfahbod wrote:
>> On 04/19/11 16:27, Alex Kerr wrote:
>>> Hello,
>> Hi Alex,
>>
>>> I'm using a really basic Cairo Pango prog as a test bed. It just displays a
>>> short string on a Cairo surface using a Pango layout, which works fine.
>>>
>>> For each glyph in the string, I now want to get it's X,Y pos (and width and
>>> height) on the rendered Cairo surface, and the PangoLogAttr data, e.g. so I
>>> could draw a box around each glyph, or whatever.
>>>
>>> After a lot of reading the API stuff, and googling for examples, I'm not quite
>>> sure how to tie the API functions together to achieve this. Anyone got any
>>> suggestions, ideas, or code please?
>> You definitely can do it with glyphs, but is that really what you want?
>> There's simpler API in pango to do that per cluster.  Note that you cannot map
>> a glyph to the original string (and hence PangoLogAttr).  You can only do that
>> per cluster.
>>
>> Check PangoLayoutIter.
>>
>> I'm also attaching Python code that draws boxes around clusters.
>>
>> Hope that helps,
>> behdad
>>
>>> Pseudocode for what I'm trying to do would be:
>>>
>>> 1. Render Pango text to Cairo surface (note: could be right-to-left, e.g.
>>> Arabic, as well as left-to-right) - Done this.
>>>
>>> 2. For each glyph (or ligature) in the line of text:
>>>      {
>>>      3. Get X, Y, Width and Height of rendered glyph (or ligature)
>>>      4. Get the PangoLogAttr structure for the same character
>>>      5. Move onto the next glyph (/ligature/character) in the line
>>>      }
>>>
>>> P.S. As a separate side note, I understand glyphs to be the separate
>>> components of a final rendered character, i.e. the main body and diacritic (if
>>> present) would be separate glyphs. Each glyph in turn could possibly be made
>>> up of more than one UTF-8 character. The rendering engine can potentially
>>> combine certain combinations of glyphs to form a single ligature. Glyphs or
>>> ligatures can also be referred to as characters (so PangoLogAttr applies to
>>> ligatures and glyphs?). Have I got this right!?
>>>
>>> Any help much appreciated :)
>>>
>>> Many thanks indeed!
>>> Alex
>>>
>>>
>>>
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