Cloth: Implement angular bending springs

This implements angular bending springs for cloth simulation. This also
adds shearing springs for n-gons.

This angular spring implementation does not include Jacobian matrices,
as the springs can exist between polygons of different vertex counts,
rendering their relationships asymmetrical, and thus impossible to solve
with the current implementation. This means that the bending component
is solved explicitly. However, this is usually not a big problem, as
bending springs contribute less to instability than structural springs.

The the old linear bending model can still be used, and is the default for
existing files, to keep compatibility. However, the new angular bending
model is the default for any new simulation.

This commit makes small breaking changes, in that shearing springs are
now created on n-gons (also in linear bending mode), while n-gons were
previously ignored.

Reviewed By: brecht

Differential Revision: http://developer.blender.org/D3662

1 files changed, 17 insertions, 11 deletions

diff --git a/source/blender/blenkernel/BKE_cloth.h b/source/blender/blenkernel/BKE_cloth.h
index a099ae46d78..baf60397504 100644
--- a/source/blender/blenkernel/BKE_cloth.h
+++ b/source/blender/blenkernel/BKE_cloth.h
@@ -133,11 +133,17 @@ ClothVertex;
 typedef struct ClothSpring {
 	int	ij;		/* Pij from the paper, one end of the spring.	*/
 	int	kl;		/* Pkl from the paper, one end of the spring.	*/
-	int mn;
-	float	restlen;	/* The original length of the spring.	*/
-	int	type;		/* types defined in BKE_cloth.h ("springType") */
-	int	flags; 		/* defined in BKE_cloth.h, e.g. deactivated due to tearing */
-	float 	stiffness;	/* stiffness factor from the vertex groups */
+	int mn;		/* For hair springs: third vertex index; For bending springs: edge index; */
+	int *pa;	/* Array of vert indices for poly a (for bending springs). */
+	int *pb;	/* Array of vert indices for poly b (for bending springs). */
+	int la;		/* Length of *pa. */
+	int lb;		/* Length of *pb. */
+	float restlen;	/* The original length of the spring. */
+	float restang;	/* The original angle of the bending springs. */
+	int	type;		/* Types defined in BKE_cloth.h ("springType"). */
+	int	flags; 		/* Defined in BKE_cloth.h, e.g. deactivated due to tearing. */
+	float lin_stiffness;	/* Linear stiffness factor from the vertex groups. */
+	float ang_stiffness;	/* Angular stiffness factor from the vertex groups. */
 	float editrestlen;
 
 	/* angular bending spring target and derivatives */
@@ -186,12 +192,12 @@ typedef enum {
 
 /* Spring types as defined in the paper.*/
 typedef enum {
-	CLOTH_SPRING_TYPE_STRUCTURAL  = (1 << 1),
-	CLOTH_SPRING_TYPE_SHEAR       = (1 << 2),
-	CLOTH_SPRING_TYPE_BENDING     = (1 << 3),
-	CLOTH_SPRING_TYPE_GOAL        = (1 << 4),
-	CLOTH_SPRING_TYPE_SEWING      = (1 << 5),
-	CLOTH_SPRING_TYPE_BENDING_ANG = (1 << 6),
+	CLOTH_SPRING_TYPE_STRUCTURAL   = (1 << 1),
+	CLOTH_SPRING_TYPE_SHEAR        = (1 << 2),
+	CLOTH_SPRING_TYPE_BENDING      = (1 << 3),
+	CLOTH_SPRING_TYPE_GOAL         = (1 << 4),
+	CLOTH_SPRING_TYPE_SEWING       = (1 << 5),
+	CLOTH_SPRING_TYPE_BENDING_HAIR = (1 << 6),
 } CLOTH_SPRING_TYPES;
 
 /* SPRING FLAGS */