Switching default texture format to DDS: Difference between revisions

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Switching default texture format to DDS (view source)

Revision as of 15:15, 4 September 2014

8,194 bytes added ,  4 September 2014
m
as per discussion with Thorsten, add DDS arguments made in 2012 - especially comments made by Mathias, who didn't participate in the recent discussion: https://www.mail-archive.com/search?q=dds+mathias&l=flightgear-devel%40lists.sourceforge.net
(Added my GPU/driver combination)
m (as per discussion with Thorsten, add DDS arguments made in 2012 - especially comments made by Mathias, who didn't participate in the recent discussion: https://www.mail-archive.com/search?q=dds+mathias&l=flightgear-devel%40lists.sourceforge.net)
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   |let's collect some some feedback until late November and restart this <br/>
   |let's collect some some feedback until late November and restart this topic. We probably know by then what we do for the next release. "Somebody" needs to collect the feedback, however. That's definitely not me - any volunteers?
topic. We probably know by then what we do for the next release.<br/>
<br/>
"Somebody" needs to collect the feedback, however. That's definitely not <br/>
me - any volunteers?<br/>
<br/>
Torsten
   |{{cite web |url=http://sourceforge.net/p/flightgear/mailman/message/32791750/
   |{{cite web |url=http://sourceforge.net/p/flightgear/mailman/message/32791750/
     |title=<nowiki>Re: [Flightgear-devel] .dds textures (was Unused and/or sourceless textures‏)</nowiki>
     |title=<nowiki>Re: [Flightgear-devel] .dds textures (was Unused and/or sourceless textures‏)</nowiki>
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== DDS Debate in 2012 (points made by Mathias)==
=== Portability Concerns  ===
These kind of precompressed images limits their usage to a specific set of drivers. And no, due to the patent issues no open source code including ours
is allowed to implement compression/decompression code for these image formats. Even if this is easy implementation wise.
I do not care for the on disk format of any image file we have. But the problem  is that some kind of precompression that can be stored in these dds files
cannot be used with other drivers than the closed ati and nvidia ones. As long as these patented compression techiques are not used, every OpenGL
driver can use this and displays this fine.
Think: Intel has the hugest marketshare in graphics today. If I remember right, they sell more than ati and nvidia together (*). This kind of change in
effect rules out the majority of users as intel cannot work with these files.
(*) There are several statistics out there, this is the intel one that counts all sold computers. AMD does usually counts the revenue made with graphics
boards (where ati wins I believe) or nvidia that usually limit statistics to professional systems (where nvidia wins).
I would like to have a flightgear that is by default just running on every average system. Having this run faster on a special configured system with some
better configuration options and hand tuned hardware and drivers is very fine. But without tuning it must at least work in an acceptable way.
I have checked in a change to flightgear to make the use of the compressed internal formats a starttime configuration option.
I am still interrested if we have that hangs also with texture compression disabled and without providing precompressed dds textures?
this is the reason for the (warning) message. If your machine would refuse to display this you, developing that, would probably just say 'nice try, but it does not work' before you check in something. In the case it displays fine, you probably say 'it works here, so I assume it works also for others, lets do'.
And the message tells you, 'despite of just seeing this working on this current machine, it does not work for others'.
Seriously, I think plenty people not being on this list today and probably never will be in touch with anybody here, will run into this issue.
People here are those few guys from the power users that want to develop this stuff.
Your driver will display this fine. So, in the end I do not care if it is 'your particular video driver' that does
not like this. You will just see this in the best case as the models look wrong, and in the worst case fgfs just crashes the driver if these textures
are used. What I really care about is that these files are expected not to work on a huge  amount of graphics boards out there. The point is to tell people doing
textures that they should omit compression so that this message disapears.
The motivation behind this mentioned change is to sort out the best compromise so that the hangs hopefully disappear - which I hope to get with precomputed
mipmaps - and being able to display fine with any driver/gpu.
=== Approaches ===
Ideas raised by Mathias in 2012 [https://www.mail-archive.com/flightgear-devel%40lists.sourceforge.net/msg35523.html]:
I have to say, that not all OpenGL drivers support texture compression, and the models with dds files, are those that I cannot display, because of that.
And in fact this will not happen to the open source drivers before something about 2020 because of patent issues.
Sorry to step in this so late - probably way too late - but is there a reason that the on disk format must be compressed?
The previous strategy to have on disk an format that everybody can read and to make the driver compress them as needed/possible is better I think?
I hope that we can get rid of the compression. Can somebody with the apropriate tools convert the compressed textures to non  compressed ones? That could still be dds, but dds without these compressions that produce the warning. So no problem with cubemaps in dds as long as the
compression is not there. Then *everybody* is again able to use this stuff.
* Just do not use the patented compression stuff. The precomputed mipmaps could probably do the job of avoiding the hangs (hopefully? to be checked?). May be we could lower disk space usage by providing a dds.gz or similar wrapper?
* If it's just the mipmaps. May be we can precompute the mipmaps using the cpu in the database loader thread. This would help all textures not only the ones that could be converted. May be this is the most generic solution.
* Implement some kind of image lookup order that knows if the compressed files could be handled or not. On loading an image in case of available compression
first try to find a dds file with the same name of the original one. That involves some 'magic' which often leads to problems but that could at least work.
Other ideas? Also may be creative ones?
Next step is to make sure that compression is not required to avoid the hangs. My favorite bet would be that then the new configure option regarding texture compression needs to be set to none.
=== Precomputed mipmaps  ===
points made by Mathias in 2012[https://www.mail-archive.com/flightgear-devel%40lists.sourceforge.net/msg37848.html]:
Could we do dds files without compression but with precomputed mipmaps?
So at next, can you try out which combination of compression/provided mipmaps/forced simgear compression still work fine?
"precompute the mipmaps in the loader. IIRC tests with some of the guys suffering from this problem, providing premipmapped but uncompressed dds files had helped to get a fluent viewer. The argument against providing these dds files in general was that these files are really huge because of not including any compression and having all the  mipmaps. 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."
computing mipmaps for any texture file on the CPU in the loader thread should globally improove the situation.
Also avoiding the compression already in the files should help every use case. Except that the on disk memory consumption is higher. Well and except that the database loader has more work to do on the CPU.
Doing that differently will provide some overhead that could be kept at a minimum I think:
For the disk usage, I think gzip compressing these will work sufficiently fine. Ram usage of the images should not hurt too much. Sure the images are bigger
in memory. But fgfs is not just about images - far from that. On the GPU, you can still use compression for the textures as the internal
format. This is what flightgear tries to do if the extension is supported (checked by osg).
The major point is that there are several ways that use slightly more resources to get around this problem.
But once the patented compression is on disk, there is *no* way back for people not having this feature.
If you have better ideas that do not rule out intel and the oss drivers, you are welcome!
On linux this should work as long as you have zlib installed which could be regarded as a system library there. Can we rely on zlib being compield into our osg distributions on win32? We do  need zlib in any case, it's mostly about teaching osg that it finds our zlib on configure and build the gz plugin.
FredB implemented a mipmap control and generation tool in effects when he last updated the urban shader. For the moment, it relies on hardware when the average  operator  is used for all texture channels but it could easily be modified to compute all mipmap on the CPU. look the <mipmap-control> effect option and
mipmap.[ch]xx in SG material lib


== Challenges ==
== Challenges ==
Retrieved from "https://wiki.flightgear.org/Special:MobileDiff/75891"

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