The idea is to stop propagating derivs through BSDFs, which we
never did properly. Instead we trace rays with radius + spread,
which we turn into OSL derivs in SG when we hit a surface. Then
when bouncing off a surface we use the BSDF roughness to set the
spread. In addition we also:
* Return BSDF samples/eval as a small struct Sample(). This
avoids output parameters in the methods.
* Stop passing a full ShaderGlobals to the BSDF methods. Pass
a viewing direction wo instead so they could run in a simpler
context.
Signed-off-by: Alejandro Conty <aconty@imageworks.com>
Alejandro Conty
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