[OpenJDK 2D-Dev] Fonts rendering in openjdk

[Phil Race]

On 5/17/2010 5:44 AM, Aekold Helbrass wrote:
> Hi again!
>
> Thanx for you fast and informative responses!
>
> But now I am a bit confused. Roman tells that Freetype does the
> rendering, but there is significant difference between Qt apps and
> Java apps. See screenthos in attachments.
>    

I think you misinterpreted. He's means that freetype produces the glyph 
images.
There's no attachment. I think these mailing lists disallow them.
freetype has several knobs, and I don't know if Qt and JDK set them all 
the same way.


> I found native code that works with freetype and changed glyph loading
> flags to the same as Qt has (i debugged it too), but they became even
> unglier.
>    

That doesn't add up.

> Phil, why pisces isn't appropriate for B&W or LCD text? Just interesting...
>    

its a grey-scale antialiasing rasteriser, not  blitting code for already 
prepared images
and grey-scale != B&W and grey-scale != LCD.

> Point me please to right direction - to make Java font rendering
> closer to Qt's should I learn pisces and compare it to Qt's rendering
> or should I debug freetype invocations?
>    

Probably look at the flags passed to freetype in each case. Revisit what 
those glyph
loading flags are.

-phil.

> Attachments:
> snapshot11 - tiny java app with DejaVu Sans Mono, Plain, 12 size font.
> snapshot12 - the same font of size 10 in KWrite.
> I assume that size (and roundness) difference is because of 72 DPI in
> Java and 96 in KDE, but difference in antialiasing is obvious.
>
> On 5/16/10, Phil Race<philip.race at oracle.com>  wrote:
>    
>> Expanding a little on Roman's comments :
>>
>> freetype is a font scaler or rasteriser. eg It takes a TrueType font and
>> returns to
>> its requester a bitmap or greymap image, or a path describing the glyph
>> shape.
>> Its role does not extend to rendering (ie putting the results of
>> rasterisation
>> on a surface). This isn't an "openjdk thing". Its just that's the role
>> of freetype.
>> Yes it also obtains the metrics in most cases.
>>
>> As Roman says there are specialised blitting routines for the text,
>> including
>> OpenGL pixel shader code, if that pipeline is optionally available and
>> enabled.
>>
>>
>> pisces isn't ever going to be the best (notably not the fastest) way to
>> get text
>> on screen and isn't appropriate for B&W or LCD text.
>>
>> -phil.
>>
>> Roman Kennke wrote:
>>      
>>> Hello,
>>>
>>>
>>>        
>>>> I want to hack into the sources of font rendering of openjdk, and I'm
>>>> a bit confused now. So help me please understand how it works. Links
>>>> are appreciated too.
>>>>
>>>> I read that freetype is used for fonts scaling, but after debugging it
>>>> looks like freetype is used only to get font metrics, while real
>>>> rendering is done using Pisces. I know nothing about real font
>>>> rendering, so I have few questions about it:
>>>> 1. am I right that freetype is used only to get font shapes while all
>>>> rendering and antialiasing is done using Pisces?
>>>>
>>>>          
>>> No, not really. The Java2D stack also gets the rendered glyphs from
>>> Freetype as bitmaps. These are displayed by pisces similar to images.
>>>
>>>
>>>        
>>>> 2. isn't freetype can be used for font rendering and is used in GTK
>>>> and Qt? Or freetype is only scaler?
>>>>
>>>>          
>>> There's the interface FontScaler in the sources (search for it). If you
>>> manage to implement this using GTK or Qt... AFAIK, GTK and Qt use
>>> Freetype themselves, so there wouldn't be any significant improvement.
>>> Plus, the FontScaler interface is quite low level, I guess you'd have a
>>> hard time implementing this using GTK or Qt, which are somwhat
>>> higher-level.
>>>
>>>
>>>        
>>>> 3. if freetype can be used for font rendering - why Pisces is used?
>>>>
>>>>          
>>> See above. Freetype does the actual rendering (anti-aliasing and such),
>>> Pisces isn't really used, the resulting bitmaps are directly blitted to
>>> the surface. Unless you're fetching the outlines and render them using
>>> draw() or such, in this case freetype doesn't do the rendering. But
>>> that's not the usual case.
>>>
>>>
>>>        
>>>> 4th and the most important - how are you guys debugging native code?
>>>> It's not supported with nbprojects, and I can't imagine how to launch
>>>> java with some application to debug some native code...
>>>>
>>>>          
>>> I prefer to use gdb. You can launch Java this way:
>>>
>>> java -XX:OnError="gdb - %p" MyApplication
>>>
>>> this jumps into gdb whenever something bad happens.
>>>
>>> Kind regards, Roman
>>>