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The parameters in this section specify the simulation behaviour for light that is transmitted directly between a light source and the current surface. In most cases, this will change how shadows casted by other objects between this source and surface will appear in images.
Set the secondary source presampling density to D. This is the number of samples per steradian that will be used to determine ahead of time whether or not it is worth following shadow rays through all the reflections and/or transmissions associated with a secondary source path. A value of 0 means that the full secondary source path will always be tested for shadows if it is tested at all.
A light source will be subdivided until the width of each sample area divided by the distance to the illuminated point is below this ratio. This assures accuracy in regions close to large area sources at a slight computational expense. A value of zero turns source subdivision off, sending at most one shadow ray to each light source.
A value of zero samples each source at specific sample points (see the Direct Sampling [-ds] option below), giving a smoother but somewhat less accurate rendering. A positive value causes rays to be distributed over each source sample according to its size, resulting in more accurate penumbras. This option should never be greater than 1, and may even cause problems (such as speckle) when the value is smaller. A warning about aiming failure will issued if frac is too large. It is usually wise to turn off image sampling when using direct jitter by setting Pixel Sampling [-ps] to 1.
Shadow testing will stop when the potential contribution of at least the next and at most all remaining light source samples is less than this fraction of the accumulated value. (See the Direct Certainty [-dc] option below.) The remaining light source contributions are approximated statistically. A value of zero means that all light source samples will be tested for shadow.
Set the number of relays for secondary sources to this value. A value of 0 means that secondary sources will be ignored. A value of 1 means that sources will be made into first generation sec ondary sources; a value of 2 means that first generation secondary sources will also be made into second generation secondary sources, and so on.
A value of one guarantees that the absolute accuracy of the direct calculation will be equal to or better than that given in the Direct Threshold [-dt] specification. A value of zero only insures that all shadow lines resulting in a contrast change greater than the Direct Threshold [-dt] specification will be calculated.
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