Am 21.07.2012 um 11:56 schrieb Harald Johnsen <hjohn...@evc.net>:
> Mathias Fröhlich a écrit :
>>
>>
>> ...
>> But that means we could at the point where the warning happens compute the
>> mipmap levels on the cpu in the loader thread. osg::gluScaleImage could be
>> used to do this I think (or something similar not requireing a context).
>> This one is an imported version of the original glu function that is
>> included in osg for running on an EGL stack which no longer provides GLU.
>> That is take the image scale this to the 1st mipmap, take the 1.st mipmap
>> and scale this to the 2. mipmap and so forth.
>>
>> This would have the advantage that the png's do not deviate from the dds
>> files over time.
>>
>
> gluScaleImage does the usual job of blurring the texture to compute the
> mipmaps.
How does that look with textures that should fit seamless? I'm really not sure
if this has to be taken into account, but when I use automated blurring (with
any algorithm) I always get the same problem, the images/mipmaps loose and you
will see structures and lines in the renderer because the textures do not fit
seamless anymore. That's something ugly I also encountered in flightgear now
with new texture work showing up, but maybe this is some texture work done with
gimp/dds and automated mipmap creation, wrong compression or whatever, I don't
know exactly. But would be really nice to see the result of automated/built-in
scaling.
> The advantage of pre computed mipmaps (inside .dds or not) is that we can use
> better algorithms (http://en.wikipedia.org/wiki/Bicubic_interpolation or
> http://en.wikipedia.org/wiki/Lanczos_resampling) to generate them.
> Perhaps gluScaleImage could be upgraded with some more algorithms ; the
> original code was trying to be fast but this is perhaps useless nowadays if
> the code runs in a separate thread.
>
>
Speaking with experience from RL work it depends heavy in which direction you
scale. Bicubic might be good for scaling up and when you don't have to much
details in a textures, when you scale down and have much detail in a texture it
might be better to use "simple" bilinear, or sophisticated lanczos? I just
started to use lanczos with gdal for tiff scaling and the result is promising.
Cheers, Yves
> HJ.
>
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