Cycles: Use curve approximation for blackbody instead of lookup table

Now we calculate color in range 800..12000 using an approximation a/x+bx+c for R and G and ((at + b)t + c)t + d) for B.
Max absolute error for RGB for non-lut function is less than 0.0001, which is enough to get the same 8 bit/channel color as for OSL with a noticeable performance difference.
However there is a slight visible difference between previous non-OSL implementation because of lookup table interpolation and offset-by-one mistake.
The previous implementation gave black color outside of soft range (t > 12000), now it gives the same color as for 12000.

Also blackbody node without input connected is being converted to value input at shader compile time.

Reviewers: dingto, sergey

Reviewed By: dingto

Subscribers: nutel, brecht, juicyfruit

Differential Revision: https://developer.blender.org/D1280

1 files changed, 0 insertions, 3 deletions

diff --git a/intern/cycles/render/shader.h b/intern/cycles/render/shader.h
index a1d697a7b7b..5bcb2c4e344 100644
--- a/intern/cycles/render/shader.h
+++ b/intern/cycles/render/shader.h
@@ -104,7 +104,6 @@ public:
 	bool has_volume;
 	bool has_displacement;
 	bool has_surface_bssrdf;
-	bool has_converter_blackbody;
 	bool has_bssrdf_bump;
 	bool has_heterogeneous_volume;
 	bool has_object_dependency;
@@ -173,10 +172,8 @@ protected:
 	AttributeIDMap unique_attribute_id;
 
 	thread_mutex lookup_table_mutex;
-	static vector<float> blackbody_table;
 	static vector<float> beckmann_table;
 
-	size_t blackbody_table_offset;
 	size_t beckmann_table_offset;
 };