With Blender 2.80 we introduced a more flexible matcap system. One
change we did was to multiply the matcap with the base color that was
shaded. As matcaps contains diffuse and specular lighting in a single
texture this lead to rendering artifacts. Artists were complaining that
everything looked to metalic.
We now support a separate `diffuse` and `specular` pass for matcaps.
`shaded_color = diffuse_light * base_color + specular_light`
For matcaps to support this feature they need to be multilayer openexr
files with 2 renderpasses (named `diffuse` and `specular`). In the future
we can change this to first pass/second pass in stead of this naming
convention.
Reviewed By: fclem, brecht
Differential Revision: https://developer.blender.org/D5335
6670019607