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diff --git a/doc/source/surface.rst b/doc/source/surface.rst new file mode 100644 index 0000000..75f3a50 --- /dev/null +++ b/doc/source/surface.rst @@ -0,0 +1,67 @@ +Surface Models +============== + +Chroma includes a variety of surface models, which control the interaction of photons with objects. The ``Surface`` class contains many (typically wavelength-dependent) surface parameters, some of which apply to each surface model. + +To select a particular model for a surface, set ``surface.model = MODEL`` where ``MODEL`` is one of ``{ SURFACE_DEFAULT, SURFACE_SPECULAR, SURFACE_DIFFUSE, SURFACE_COMPLEX, SURFACE_WLS }``. + +``SURFACE_DEFAULT`` +------------------- + +The default surface model approximates real surfaces by combining a diffuse and specular reflection component. Surfaces may also be absorbing and detecting. The wavelength-dependent probabilities for detection, absorption, diffuse reflection, and specular reflection are provided in uniformly-spaced float arrays of length ``n``, and should sum to unity. The corresponding wavelengths for these arrays are computed from the first (``wavelength0``) and the step size (``step``). + +Parameters:: + + float *detect + float *absorb + float *reflect_diffuse + float *reflect_specular + unsigned int n + float step + float wavelength0 + +``SURFACE_SPECULAR`` +-------------------- + +A perfect specular reflector. Behavior is identical to ``SURFACE_DEFAULT`` with 100% specular reflection at all wavelengths, but is marginally faster. This model has no parameters. + +``SURFACE_DIFFUSE`` +------------------- + +A perfect diffuse reflector. Behavior is identical to ``SURFACE_DEFAULT`` with 100% diffuse reflection at all wavelengths, but is marginally faster. This model has no parameters. + +``SURFACE_COMPLEX`` +------------------- + +This surface model uses a complex index of refraction (``eta``, ``k``) to compute transmission, (specular) reflection, and absorption probabilities. Surfaces may also be photon detectors, but the detection probability is conditional on detection (``detect`` should be normalized to 1). If a surface is not transmissive (``bool transmissive``), transmitted photons are absorbed. + +This model accounts for incoming photon polarization in its calculations. + +Parameters:: + + float *detect + float *eta + float *k + unsigned int n + float step + float wavelength0 + float thickness + bool transmissive + +``SURFACE_WLS`` +--------------- + +A model of wavelength-shifting surfaces. Surfaces may absorb and reflect (these probabilities should sum to 1). Reflection is diffuse. If a photon is absorbed, it may be reemitted with a probability given in ``float *reemit`` (normalized to 1). The reemission spectrum CDF is defined in ``float* reemission_wavelength`` (x) and ``float* reemission_cdf`` (y), both of length ``reemission_n``. The CDF must start at 0 and end at 1. This model does not enforce conservation of energy, and cannot reemit multiple photons! + +Parameters:: + + float *absorb + float *reflect + float *reemit + float *reemission_wavelength + float *reemission_cdf + unsigned int n + unsigned int reemission_n + float step + float wavelength0 + |