Cycles: Mark pixels with negative values as outliers

If a pixel has negative components, something already went wrong, so the best option is to just ignore it.

Should be good for 2.79.

Cycles: Mark pixels with negative values as outliers

If a pixel has negative components, something already went wrong, so the best option is to just ignore it.

Should be good for 2.79.

Fix T52280: The Image node in Compositing can't read Z buffer of openEXR in 2.79

As part of the fix for T51587, I removed the Depth output for non-Multilayer
images since it seemed weird that PNGs etc. that don't have a Z pass still get
a socket for it.
However, I forgot about non-multilayer EXRs, which are a special case that can
actually have a Z pass.

Therefore, this commit brings back the Depth output for non-multilayer images
just like it was in 2.78.

Cycles: Calculate correct remaining time when using a larger pixel size

Cycles/BI: Add a pixel size option for speeding up viewport rendering

This patch adds "Pixel Size" to the performance options, which allows to render
in a smaller resolution, which is especially useful for displays with high DPI.

Reviewers: Severin, dingto, sergey, brecht

Reviewed By: brecht

Subscribers: Severin, venomgfx, eyecandy, brecht

Differential Revision: https://developer.blender.org/D1619

Fix T52280: The Image node in Compositing can't read Z buffer of openEXR in 2.79

As part of the fix for T51587, I removed the Depth output for non-Multilayer
images since it seemed weird that PNGs etc. that don't have a Z pass still get
a socket for it.
However, I forgot about non-multilayer EXRs, which are a special case that can
actually have a Z pass.

Therefore, this commit brings back the Depth output for non-multilayer images
just like it was in 2.78.

Fix T51950: Abnormally long Cycles OpenCL GPU render times with certain panoramic camera settings

The problem here was that when a "invalid" path is generated by the panoramic camera, it was tagged
as RAY_TO_REGENERATE with the intention of generating a new path in kernel_buffer_update.

However, since that state was not handled in kernel_queue_enqueue, kernel_buffer_update did not
process the path which resulted in an infinite loop.

Cycles: Add missing split kernel to CPUDevice

Fix T51909: Cycles: Uninitialized closure normals for the Hair BSDF

As the title says, the normal wasn't set for the Hair BSDF because it wasn't
needed before. However, the denoiser uses it to store the feature passes, so
it needs to be set now.

Fix T51836: Cycles: Fix incorrect PDF approximations of the MultiGGX closures

The PDF of the MultiGGX sampling is approximated by the singlescattering GGX
term as well as a scaled diffuse term that makes up for the energy in the
multiscattering component that's missed by GGX.

However, there were two problems with the glossy terms: The diffuse term missed
a normalization factor, and the singlescattering term was not properly scaled
down based on the albedo estimate.

The glass term was completely wrong and has been rewritten. It uses the fresnel
factor to weight reflection vs. refraction and uses the glossy MultiGGX model
for reflection.
For refraction, the correct singlescattering term is now used, and a new
albedo approximation is used that was derived by evaluating GGX albedo for
roughnesses from 0 to 1 and IORs from 1 to 3 and fitting numerical
approximations to it. The resulting model has a mean relative error of 9e-5,
but could probably be simplified without losing noticable accuracy in the
final render.

The improved PDFs help with glossy highlights (due to better light sampling vs.
closure sampling MIS) and fix the situation described in T51836 where mixing
MultiGGX with other closures (as it happens in e.g. the Principled
BSDF) causes incorrect darkening.