CompositeGlyph question..

[Mohan Parthasarathy]

On Thu, Jul 24, 2008 at 1:01 PM, Mohan Parthasarathy <suruti94 at gmail.com>
wrote:

>
>>
>>
>> >         for a single composite operation to the destination picture in
>> >         order to
>> >         actually render the glyphs. Without a mask format, each glyph
>> >         is used as
>> >         a mask for a composite operation to the destination picture
>> >         directly.
>> >
>> >         The result should be visually identical unless the mask format
>> >         is
>> >         different from any of the glyphs or the glyphs overlap.
>> >
>> > Thanks for the explanation. Do we know how this is done in practice ?
>> > I am trying to understand the sequence of operations
>> >
>> > 1) The client adds glyphs to the server
>> > 2) The client calls CompositeGlyph with a non-null format
>> > 3) The client calls CompositeGlyph with a null-format and a
>> > destination picture
>> >
>> > Is (2) and (3) done separately or just (3) is done ?
>>
>> I'm not sure I understand. (2) needs a destination as well, so (2) and
>> (3) should be essentially identical, with the caveats I mentioned above.
>>
>
> Ah!, when non-null maskFormat is passed, the first composite operation the
> Mask
> is the destination. But then the second composite operation needs a
> destination
> also. I am understanding slightly better after reading your mail again and
> the code
> again :-)
>
> What i am trying to understand is what exactly happens
> when i need to display characters on my xterm ? I can see that glyphs are
> added to the Xserver. Later a Composite operation is called by the client.
> As the maskFormat argument can be null, i am wondering what cases it
> is null and what cases it is not null. Initially, i thought you always need
> to
> composite Glyph with Mask and then composite to the destination which
> means maskFormat will always be non-null. Obviously, this is not the case.
> So, to render characters on my xterm, i can just send src, dst and glyph
> with a
> null mask. Is this sufficient ? What cases would require me to pass a
> non-null
> mask ? What am i missing ?
>

Sorry to reply to my own mail.. Looking at Xft, i figured that when the font
files
are loaded, font->format is initialized using XRenderFindStandardFormat.
This
is what is used for mask later XRenderCompositeString. It is possible that
the format can be null if is Older font. This can explain when the mask can
be
null and when it is not null.

Does that make sense ?

thanks
mohan




>
> thanks
> mohan
>
>>
>>
>> >         > I searched around in Xft and server side to see where this
>> >         code is
>> >         > implemented. I can see that in libXrender, maskFormat
>> >         getting set to
>> >         > None or the id. So, it has to be on the server side Perhaps,
>> >         i am
>> >         > missing something very obvious.. Can someone point me to
>> >         this code ?
>> >
>> >
>> >         miGlyphs() in render/glyph.c or exaGlyphs() in
>> >         exa/exa_glyphs.c .
>> >
>> > I sort of figured that out working backwards from exaCompositeRects ->
>> > exaGlyphstoMask...
>> > But could not find out when the mask is set to null or not-null.
>>
>> I think it's simply NULL if the client passes None as maskFormat
>> parameter to XRenderCompositeString/Text*() and non-NULL otherwise.
>>
>>
>> --
>> Earthling Michel Dänzer           |          http://tungstengraphics.com
>> Libre software enthusiast         |          Debian, X and DRI developer
>>
>>
>
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