Re: [Flightgear-devel] Functions to textures?
> Actually, the code that creates the texture is in > scene/util/StateAttributeFactory.cxx, but you would have to do > something similar to the noise texture code in TextureBuilder to > access your texture from a texture. It would be nice if the Effects > framework had a way to load arbitrary textures and make them available > to effects. > > These days you aren't limited to 8 bit texture components. There is a > rich set of data formats for textures: 32 bit floats, 16 bit floats, > exotic combinations of different length floats per RGB component... I > don't know if there is a better way to create your texture offline > than write C++ code in simgear. OSG will read a TIFF file with 32bits > per component as a floating point texture... assuming you can create > such a thing. Thanks for the explanations and locations. After some experiments, it seems the way to do this is to implement the noise function directly as GLSL code in the fragment shader. This has a whole bunch of advantages: 1) Creating a 4-component noise vector corresponding to what is in the texture beats the texture lookup call by (very roughly) ~20% on my system 2) Unlike a noise texture, noise generated on the fly never has tiling artefacts, so there is no need to superimpose nearby wavelengths in the first place, saving between a third and half of the total use of noise 3) Unlike texture lookup, the noise function can be evaluated just when needed, even inside a non-uniform conditional,i.e. for instance respecting a distance cut which makes a lot of sense for LOD, again that saves a lot of un-needed work (and 4), I can write it in a completely intuitive way by passing a wavelength in and getting a number between 0 and 1 out, so there's no need to do any re-scaling and mental arithmetics). So, that just means I have to change a few numbers everywhere... * Thorsten -- Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] Functions to textures?
On Wed, Jul 25, 2012 at 12:16 AM, Chris Forbes wrote: >> 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. > > That depends a lot on the GPU, and how coherent the texture > coordinates are across a triangle. You also need enough ALU work > elsewhere in the shader to mask the latency of the texture lookup. > > For the existing noise texture generation, take a look at > make3DNoiseImage in scene/material/TextureBuilder.cxx in the simgear > tree. This particular texture is filled CPU-side, but if you're more > comfortable expressing things in a shader, you/someone could rig up > some FBO wiring to quickly render a shader-defined function into a > texture. Actually, the code that creates the texture is in scene/util/StateAttributeFactory.cxx, but you would have to do something similar to the noise texture code in TextureBuilder to access your texture from a texture. It would be nice if the Effects framework had a way to load arbitrary textures and make them available to effects. These days you aren't limited to 8 bit texture components. There is a rich set of data formats for textures: 32 bit floats, 16 bit floats, exotic combinations of different length floats per RGB component... I don't know if there is a better way to create your texture offline than write C++ code in simgear. OSG will read a TIFF file with 32bits per component as a floating point texture... assuming you can create such a thing. Tim -- Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] Functions to textures?
> 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. That depends a lot on the GPU, and how coherent the texture coordinates are across a triangle. You also need enough ALU work elsewhere in the shader to mask the latency of the texture lookup. For the existing noise texture generation, take a look at make3DNoiseImage in scene/material/TextureBuilder.cxx in the simgear tree. This particular texture is filled CPU-side, but if you're more comfortable expressing things in a shader, you/someone could rig up some FBO wiring to quickly render a shader-defined function into a texture. -- Chris -- Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] Functions to textures?
On Tue, 24 Jul 2012 07:02:44 +, 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? http://www.paulgraham.com/icad.html http://www.paulgraham.com/avg.html -- ..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. -- Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
