Simple hair children: Make twist affected by texture

This completes twist feature, which is now possible to also control by
texture. Since textures can not easily contain negative values as well,
same trick with 0.5 neutral as vertex groups is used.

All in all, this twist features allows to do following things.

Original hair:

{F2287535}

Hair with scientifically calculated twist value of 0.5:

{F2287540}

And we can also twist braids in opposite directions dependent on left/right
side:

{F2287548}

2 files changed, 3 insertions, 2 deletions

diff --git a/source/blender/makesdna/DNA_particle_types.h b/source/blender/makesdna/DNA_particle_types.h
index 8dd4d46a596..9dbd1a18703 100644
--- a/source/blender/makesdna/DNA_particle_types.h
+++ b/source/blender/makesdna/DNA_particle_types.h
@@ -614,7 +614,8 @@ typedef enum eParticleTextureInfluence {
 	PAMAP_KINK_AMP	= (1<<12),
 	PAMAP_ROUGH		= (1<<9),
 	PAMAP_LENGTH	= (1<<4),
-	PAMAP_CHILD		= (PAMAP_CLUMP | PAMAP_KINK_FREQ | PAMAP_KINK_AMP | PAMAP_ROUGH | PAMAP_LENGTH),
+	PAMAP_TWIST	= (1<<13),
+	PAMAP_CHILD		= (PAMAP_CLUMP | PAMAP_KINK_FREQ | PAMAP_KINK_AMP | PAMAP_ROUGH | PAMAP_LENGTH | PAMAP_TWIST),
 } eParticleTextureInfluence;
 
 #endif
diff --git a/source/blender/makesdna/DNA_texture_types.h b/source/blender/makesdna/DNA_texture_types.h
index 995d7645dc0..0eb54a9b5b3 100644
--- a/source/blender/makesdna/DNA_texture_types.h
+++ b/source/blender/makesdna/DNA_texture_types.h
@@ -86,7 +86,7 @@ typedef struct MTex {
 	float timefac, lengthfac, clumpfac, dampfac;
 	float kinkfac, kinkampfac, roughfac, padensfac, gravityfac;
 	float lifefac, sizefac, ivelfac, fieldfac;
-	int pad2;
+	float twistfac;
 
 	/* lamp */
 	float shadowfac;