Shrinkwrap: new mode that projects along the target normal.

The Nearest Surface Point shrink method, while fast, is neither
smooth nor continuous: as the source point moves, the projected
point can both stop and jump. This causes distortions in the
deformation of the shrinkwrap modifier, and the motion of an
animated object with a shrinkwrap constraint.

This patch implements a new mode, which, instead of using the simple
nearest point search, iteratively solves an equation for each triangle
to find a point which has its interpolated normal point to or from the
original vertex. Non-manifold boundary edges are treated as infinitely
thin cylinders that cast normals in all perpendicular directions.

Since this is useful for the constraint, and having multiple
objects with constraints targeting the same guide mesh is a quite
reasonable use case, rather than calculating the mesh boundary edge
data over and over again, it is precomputed and cached in the mesh.

Reviewers: mont29

Differential Revision: https://developer.blender.org/D3836

1 files changed, 12 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/DerivedMesh.c b/source/blender/blenkernel/intern/DerivedMesh.c
index c84bd378b04..1d787388774 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.c
+++ b/source/blender/blenkernel/intern/DerivedMesh.c
@@ -75,6 +75,7 @@
 
 #include "DEG_depsgraph.h"
 #include "DEG_depsgraph_query.h"
+#include "BKE_shrinkwrap.h"
 
 #ifdef WITH_OPENSUBDIV
 #  include "DNA_userdef_types.h"
@@ -1980,6 +1981,15 @@ static void mesh_finalize_eval(Object *object)
 	}
 }
 
+static void mesh_build_extra_data(struct Depsgraph *depsgraph, Object *ob)
+{
+	uint32_t eval_flags = DEG_get_eval_flags_for_id(depsgraph, &ob->id);
+
+	if (eval_flags & DAG_EVAL_NEED_SHRINKWRAP_BOUNDARY) {
+		BKE_shrinkwrap_compute_boundary_data(ob->runtime.mesh_eval);
+	}
+}
+
 static void mesh_build_data(
         struct Depsgraph *depsgraph, Scene *scene, Object *ob, CustomDataMask dataMask,
         const bool build_shapekey_layers, const bool need_mapping)
@@ -2016,6 +2026,8 @@ static void mesh_build_data(
 	}
 
 	BLI_assert(!(ob->derivedFinal->dirty & DM_DIRTY_NORMALS));
+
+	mesh_build_extra_data(depsgraph, ob);
 }
 
 static void editbmesh_build_data(