fixed default value for frame pixel format widget, missing in cb1361633203080a33589b6f4b6f2fc0af0ebdc6: "switched default frame pixel format format from 32-bit float to 16-bit float (half)".
in the microfacet BRDF, renamed the mdf_parameter and mdf_parameter_multiplier inputs to glossiness and glossiness_multiplier, and normalized glossiness into [0, 1] for all distribution functions.