EnvConvolve

This is a fast (FFT-based) approximation of brute force environment map convolution a la HDR Shop, using a Phong BRDF.  The output image is seamless and can be diffuse or specular.  The input image should be in latlong space.

A typical brute force convolution will apply the BRDF oriented at each pixel and then do a weighted sum of the result.  This gizmo is simply applying an FFT Convolve in angular map space using a Phong BRDF as the kernel but it's only doing it in +Z and -Z directions then blending them together.  

For a pure diffuse surface set the exponent to 1.  For a glossy to highly specular surface set it higher.

v1.1 - Improved blending a bit and got rid of the size knob.  The output res is now determined by the input res.

v1.2 - Added a CopyBBox to make sure the outgoing bounding box matches the input.

v1.3 - Correctly deals with proxy mode.

v1.4 - Another proxy mode fix...