“nslib_particle_ptex” (Fig 22-1) is a particle texture shader which provides the per-particle texture mapping (don't confuse it with the per-face texture mapping). Its displayed name in the material browser is “Particle Texture PTex (NSLIB)”.
The first parameter is “input” which should be connected to a texture shader, nslib_particle_ptex will provide a local coordinate of the particle for texture mapping, so the texture will stick to the particles without the swimming artifact (for more details, see here). For example, you can assign the Noise shader to “input” (Fig 22-2). Turn on the “normalize” parameter will scale the texture coordinate with the particle size, in this way, the texture size will grow with the particle size. When this parameter has been turned on, the size control of the connected texture shader should be set to a constant, for example 1.0 (Fig 22-3).
The “falloff” parameter controls the attenuation of the texture, the attenuation begins at the center of the particle and fades to zero at the border of it. The default value is 0.5, set it to 0.0 will disable it, increase it will cause rapider fading. If you use nslib_particle_ptex to modify the density of the particles, turning on “falloff” could alleviate the dim border issue of Photon Illumination (see here). But if you use nslib_particle_ptex to modify the scattering color of the particles, the “falloff” should be disabled because it's not necessary in this case.
When the motion blurring of the particles was turned on (Fig 22-4), we need to sample the input texture multiple times to get a blurred result. The parameter “step” in the “Motion Blurring” rollout determines how many samples will be taken. Generally, if the “normalize” is on, set “step” to 1.0 will be a good start. Increase it for faster preview, decrease it for better quality.
Again, as a particle texture shader like the nslib_particle_age (here), nslib_particle_ptex needs the cooperation with the particle volume shaders, you should not apply it to any other shaders.
Fig 16-9, Fig 16-10 (here), Fig 19-3 (here) and Fig 20-1 (here) are rendered with nslib_particle_ptex.