Cloth: Fix the shrink feature to be controlled by the sewing spring flag.

Previously it was all over the place: without a vertex group it was
always enabled, and with it it depended on the Self Collision option
due to a likely editing mistake. Now it should be in sync with what
disables the fields in the UI.

The verts->shrink_factor field is changed to just cache the vertex
weight, with the shrink_min/shrink_max interpolation done later.
This is because cloth_apply_vgroup only runs if there are vertex
groups, and thus the factor may not update after property changes.

In addition, bending springs are now also affected by the shrink
factor to avoid visible distortion in object shape at high shrink.

1 files changed, 26 insertions, 15 deletions

diff --git a/source/blender/blenkernel/intern/cloth.c b/source/blender/blenkernel/intern/cloth.c
index 7a2a4e09b3d..137b6a3d599 100644
--- a/source/blender/blenkernel/intern/cloth.c
+++ b/source/blender/blenkernel/intern/cloth.c
@@ -644,6 +644,7 @@ int cloth_uses_vgroup(ClothModifierData *clmd)
 {
 	return (((clmd->sim_parms->flags & CLOTH_SIMSETTINGS_FLAG_SCALING ) || 
 		(clmd->sim_parms->flags & CLOTH_SIMSETTINGS_FLAG_GOAL ) ||
+		(clmd->sim_parms->flags & CLOTH_SIMSETTINGS_FLAG_SEW) ||
 		(clmd->coll_parms->flags & CLOTH_COLLSETTINGS_FLAG_SELF)) && 
 		((clmd->sim_parms->vgroup_mass>0) || 
 		(clmd->sim_parms->vgroup_struct>0)||
@@ -684,6 +685,9 @@ static void cloth_apply_vgroup ( ClothModifierData *clmd, DerivedMesh *dm )
 			else
 				verts->goal= 0.0f;
 
+			/* Compute base cloth shrink weight */
+			verts->shrink_factor = 0.0f;
+
 			/* Reset vertex flags */
 			verts->flags &= ~CLOTH_VERT_FLAG_PINNED;
 			verts->flags &= ~CLOTH_VERT_FLAG_NOSELFCOLL;
@@ -721,16 +725,14 @@ static void cloth_apply_vgroup ( ClothModifierData *clmd, DerivedMesh *dm )
 								verts->flags |= CLOTH_VERT_FLAG_NOSELFCOLL;
 							}
 						}
-
+					}
+					if ( clmd->sim_parms->flags & CLOTH_SIMSETTINGS_FLAG_SEW ) {
 						if (clmd->sim_parms->vgroup_shrink > 0) {
 							if (dvert->dw[j].def_nr == (clmd->sim_parms->vgroup_shrink - 1)) {
-								/* linear interpolation between min and max shrink factor based on weight */
-								verts->shrink_factor = clmd->sim_parms->shrink_min * (1.0f - dvert->dw[j].weight) + clmd->sim_parms->shrink_max * dvert->dw [j].weight;
+								/* used for linear interpolation between min and max shrink factor based on weight */
+								verts->shrink_factor = dvert->dw[j].weight;
 							}
 						}
-						else {
-							verts->shrink_factor = clmd->sim_parms->shrink_min;
-						}
 					}
 				}
 			}
@@ -738,6 +740,18 @@ static void cloth_apply_vgroup ( ClothModifierData *clmd, DerivedMesh *dm )
 	}
 }
 
+static float cloth_shrink_factor(ClothModifierData *clmd, ClothVertex *verts, int i1, int i2)
+{
+	if ( clmd->sim_parms->flags & CLOTH_SIMSETTINGS_FLAG_SEW ) {
+		/* linear interpolation between min and max shrink factor based on weight */
+		float base = 1.0f - clmd->sim_parms->shrink_min;
+		float delta = clmd->sim_parms->shrink_min - clmd->sim_parms->shrink_max;
+
+		return base + delta * 0.5f * (verts[i1].shrink_factor + verts[i2].shrink_factor);
+	}
+	else
+		return 1.0f;
+}
 
 static int cloth_from_object(Object *ob, ClothModifierData *clmd, DerivedMesh *dm, float UNUSED(framenr), int first)
 {
@@ -811,6 +825,8 @@ static int cloth_from_object(Object *ob, ClothModifierData *clmd, DerivedMesh *d
 		else
 			verts->goal= 0.0f;
 
+		verts->shrink_factor = 0.0f;
+
 		verts->flags = 0;
 		copy_v3_v3 ( verts->xold, verts->x );
 		copy_v3_v3 ( verts->xconst, verts->x );
@@ -1237,10 +1253,7 @@ static int cloth_build_springs ( ClothModifierData *clmd, DerivedMesh *dm )
 				spring->type = CLOTH_SPRING_TYPE_SEWING;
 			}
 			else {
-				if (clmd->sim_parms->vgroup_shrink > 0)
-					shrink_factor = 1.0f - ((cloth->verts[spring->ij].shrink_factor + cloth->verts[spring->kl].shrink_factor) / 2.0f);
-				else
-					shrink_factor = 1.0f - clmd->sim_parms->shrink_min;
+				shrink_factor = cloth_shrink_factor(clmd, cloth->verts, spring->ij, spring->kl);
 				spring->restlen = len_v3v3(cloth->verts[spring->kl].xrest, cloth->verts[spring->ij].xrest) * shrink_factor;
 				spring->stiffness = (cloth->verts[spring->kl].struct_stiff + cloth->verts[spring->ij].struct_stiff) / 2.0f;
 				spring->type = CLOTH_SPRING_TYPE_STRUCTURAL;
@@ -1287,10 +1300,7 @@ static int cloth_build_springs ( ClothModifierData *clmd, DerivedMesh *dm )
 				        mloop[mpoly[i].loopstart + (j + 0)].v,
 				        mloop[mpoly[i].loopstart + (j + 2)].v);
 
-				if (clmd->sim_parms->vgroup_shrink > 0)
-					shrink_factor = 1.0f - ((cloth->verts[spring->ij].shrink_factor + cloth->verts[spring->kl].shrink_factor) / 2.0f);
-				else
-					shrink_factor = 1.0f - clmd->sim_parms->shrink_min;
+				shrink_factor = cloth_shrink_factor(clmd, cloth->verts, spring->ij, spring->kl);
 				spring->restlen = len_v3v3(cloth->verts[spring->kl].xrest, cloth->verts[spring->ij].xrest) * shrink_factor;
 				spring->type = CLOTH_SPRING_TYPE_SHEAR;
 				spring->stiffness = (cloth->verts[spring->kl].shear_stiff + cloth->verts[spring->ij].shear_stiff) / 2.0f;
@@ -1334,7 +1344,8 @@ static int cloth_build_springs ( ClothModifierData *clmd, DerivedMesh *dm )
 					}
 
 					spring_verts_ordered_set(spring, tspring2->ij, index2);
-					spring->restlen = len_v3v3(cloth->verts[spring->kl].xrest, cloth->verts[spring->ij].xrest);
+					shrink_factor = cloth_shrink_factor(clmd, cloth->verts, spring->ij, spring->kl);
+					spring->restlen = len_v3v3(cloth->verts[spring->kl].xrest, cloth->verts[spring->ij].xrest) * shrink_factor;
 					spring->type = CLOTH_SPRING_TYPE_BENDING;
 					spring->stiffness = (cloth->verts[spring->kl].bend_stiff + cloth->verts[spring->ij].bend_stiff) / 2.0f;
 					BLI_edgeset_insert(edgeset, spring->ij, spring->kl);