Workbench: Use non-negative lighting evaluation

This makes the lighting a bit more diffuse but don't produce negative
values.

Add a bias of 1.5f to make the lighting a bit more directionnal.

The implementation is based on:
https://github.com/kayru/Probulator/blob/master/Source/Probulator/SphericalHarmonics.h#L136
which is derived from:
http://www.geomerics.com/wp-content/uploads/2015/08/CEDEC_Geomerics_ReconstructingDiffuseLighting1.pdf

The shader implementation is optimized and has the same runtime cost
as previous method:
* no sh eval : 0.13ms
* prev sh eval : 0.14ms
* new sh eval : 0.22ms
* new sh eval opti : 0.14ms

1 files changed, 3 insertions, 1 deletions

diff --git a/source/blender/draw/engines/workbench/workbench_private.h b/source/blender/draw/engines/workbench/workbench_private.h
index ef18c00cff3..93b3bddfb72 100644
--- a/source/blender/draw/engines/workbench/workbench_private.h
+++ b/source/blender/draw/engines/workbench/workbench_private.h
@@ -138,8 +138,10 @@ typedef struct WORKBENCH_UBO_Light {
 	float energy;
 } WORKBENCH_UBO_Light;
 
+#define WORKBENCH_SH_DATA_LEN ((STUDIOLIGHT_SH_BANDS == 2) ? 6 : STUDIOLIGHT_SH_EFFECTIVE_COEFS_LEN)
+
 typedef struct WORKBENCH_UBO_World {
-	float spherical_harmonics_coefs[STUDIOLIGHT_SH_EFFECTIVE_COEFS_LEN][4];
+	float spherical_harmonics_coefs[WORKBENCH_SH_DATA_LEN][4];
 	float background_color_low[4];
 	float background_color_high[4];
 	float object_outline_color[4];