Re: [Flightgear-devel] Functions to textures?

[Tim M. <tim...@gm...>]

On Wed, Jul 25, 2012 at 12:16 AM, Chris Forbes <ch...@ij...> 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