Target calculation for local non-straight rest shapes.

This is more involved than using simple straight bending targets
constructed from the neighboring segments, but necessary for restoring
groomed rest shapes.

The targets are defined by parallel-transporting a coordinate frame
along the hair, which smoothly rotates to avoid sudden twisting (Frenet
frame problem). The rest positions of hair vertices defines the target
vectors relative to the frame. In the deformed motion state the frame
is then recalculated and the targets constructed in world/root space.

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index 56923b6603a..458a8f27ee7 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -426,6 +426,13 @@ BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s,
 		
 		/* XXX assuming same restlen for ij and jk segments here, this can be done correctly for hair later */
 		BPH_mass_spring_force_spring_bending_angular(data, s->ij, s->kl, s->mn, s->matrix_ij_kl, s->matrix_kl_mn, s->matrix_ij_mn, s->restlen, s->restlen, kb, cb);
+		
+		{
+			float x[3], v[3], d[3];
+			BPH_mass_spring_get_motion_state(data, s->kl, x, v);
+			mul_v3_v3fl(d, s->target, clmd->sim_parms->avg_spring_len);
+			BKE_sim_debug_data_add_vector(clmd->debug_data, x, d, 0.4, 0.4, 1, "target", hash_vertex(7982, s->kl));
+		}
 #endif
 	}
 }