On Tue, 24 Jul 2012 07:02:44 +0000, Renk wrote in message 

> First of all, a big thanks to Tim - Akenine-Moller &Co. is indeed
> quite an interesting read, and in addition to gaining a better
> understanding, I've so far experimented successfully with a
> heightfield for parallax and normal mapping and a simple irrandiance
> map instead of the ambient term in lighting. 
> For those not inclined to read through a longer email, my question up
> front: I have a function, I want a texture holding the function
> values  pairs - how do I map this without editing every pixel
> offline? And can we do this also online? Where is for instance the 3d
> noise texture defined and filled - is it simple to change the
> procedure?
> For those interested in the context:
> I have managed to create quite compelling terrain visuals from
> close-up (see here
> http://www.flightgear.org/forums/viewtopic.php?f=47&t=16884&start=15#p162613
> for two examples), but rendering seems to get too slow too soon for
> anything really fancy (of course, a big roadblock is that I'm
> implementing all this on top of atmospheric light scattering which is
> slow to begin with - I think in the default light and fog scheme it
> might run with decent speed).
> One problem that really kills framerate is de-tiling. In order to
> de-tile properly, one needs to mix noise from different wavelengths
> such that the interference creates a pattern with a much larger
> periodicity. Three wavelengths usually do the job well, two are
> marginally acceptable, one is quite bad.
> So, for each texture component (snow, gradient texture, detailed
> texture, height map, fog) I ideally need three noise wavelengths. In
> the current 3d noise, noise[0] contains structures with a
> qualitatively different distribution, so I have to discard that
> component. noise[3] is too fine and runs into texture resolution
> problems, so I have to discard that as well. Since the noise pattern
> associated with different texture components needs to be uncorrelated
> (otherwise there's yet another form of tiling around the corner) I
> need to do different noise lookups for every texture component,
> arranging them in a slightly different wavelength interval.
> And that's a lot of texture3D() calls which really make the system
> slow.
> I could do it in half the time if I would get 4 useful components for
> every texture3D() call, but that requires that I either create a
> suitable texture offline or change the way it is done in the code
> (I'm also exploring if there is perhaps a function that evaluates
> faster than a texture lookup call...).
> Somewhat inversely, I'm also wondering if a simple texture1D() lookup
> might not be faster than evaluating the light function e / pow((1.0 +
> a * exp(-b * (x-c)) ),(1.0/d)) three times to get an (rgb)-triplet.
> However, I have no clue how to dump the function into a texture
> without hand-crafting every pixel.
> Finally, I think given that we have cloud position and sizes
> available, it'd be fairly trivial to cast that into a function that
> defines a shadow-map for clouds (I would not render the clouds to
> create that map, first because of transparency, second because
> they're really billboards and likely to come out wrong, third because
> the map wouldn't change fast and finally because it's faster to do
> one analytical function per cloudlet than to go through the 40
> texture sheets that are in a cloudlet.
> So, any pointers along that front would be appreciated for a number
> of reasons... Thanks in advance!

..maybe this is a place for Lisp?

..med vennlig hilsen = with Kind Regards from Arnt Karlsen
...with a number of polar bear hunters in his ancestry...
  Scenarios always come in sets of three: 
  best case, worst case, and just in case.

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