On Friday 27 April 2012 06:50:22 Renk Thorsten wrote:
>
> Thank you for the info - that's good to know (although admittedly I have to
> do some reading trying to understand what 'that' precisely is - the linked
> article is a bit opaque for me). Seems there's a lot to learn about the
> hidden secrets of GLSL...
>
> Since this doesn't look like a crippling issue (it seems to work on my card
> just fine, it potentially affects only higher detail settings,...) I would
> like to take the time and understand what is going on before making any
> changes. The reason is that things end up in conditionals usually because I
> tested them to have better performance, so just pulling them out would
> degrade performance again. The article seems to suggest a different syntax
> to do conditional texture lookup inside an if clause, so I would like to
> look into that and compare performance in some benchmarks.
>
> I would also be intersted if anyone is actually seeing any texturing
> artefacts (should be mainly the snow effect) caused by the issue, so that I
> can see if I implemented a fix correctly, because on my system it's running
> fine as it is.
>
> Thanks,
>
> * Thorsten
Found the original article describing the issue
http://www.opengl.org/img/uploads/pipeline/pipeline_001.pdf
page 3, " New Texture Functions with Awkward
Names to Avoid Ugly Artifacts"
The new functions require the extensions present, and a port of the shader to
glsl 1.40. And even then they may or may not be properly supported by
different cards. So the simple solution is to pull them out of the
conditional.
I have hit this with the transition shader, it worked fine on different cards,
but it blew up the mipmap lookup on a card similar to mine:
http://flightgear.org/forums/viewtopic.php?f=5&t=13513&hilit=dds+textures#p136566
check the "cornrows" in the distance on the forest areas.
The usage of custom miplevels made it more obvious and easy to spot, but the
effects of these can range from a small discontinuity in the features to the
shader eroring on some other implementations.
Regards
Emilian
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