[Bf-blender-cvs] [929aa7c046] cloth-improvements: Fix plasticity issue with shearing springs

[Luca Rood]

Commit: 929aa7c046241cab156f51ff1033e7dbbca4c5b5
Author: Luca Rood
Date:   Fri Jan 6 04:44:13 2017 -0200
Branches: cloth-improvements
https://developer.blender.org/rB929aa7c046241cab156f51ff1033e7dbbca4c5b5

Fix plasticity issue with shearing springs

===================================================================

M	source/blender/physics/intern/implicit_blender.c

===================================================================

diff --git a/source/blender/physics/intern/implicit_blender.c b/source/blender/physics/intern/implicit_blender.c
index d91136ba53..42958790e9 100644
--- a/source/blender/physics/intern/implicit_blender.c
+++ b/source/blender/physics/intern/implicit_blender.c
@@ -1635,6 +1635,14 @@ bool BPH_mass_spring_force_spring_linear(Implicit_Data *data, int i, int j, floa
 	else {
 		zero_v3(f);
 		zero_m3(dfdx);
+
+		/* compute plasticity offset factor */
+		/* plasticity has to be computed even for non-compressive springs in a compression condition,
+		 * otherwise issues occur where shearing gets unconstrained when cloth undergoes compression */
+		if (length < restlen / yield_fact) {
+			restlen -= (restlen - (length * yield_fact)) * plasticity;
+			*lenfact = restlen / restlenorig;
+		}
 	}
 
 	/* Calculate damping forces */