Multires: Fix Subdivide, Reshape and Apply Base

This change fixes artifacts produced by these operations.

On a technical aspect this is done by porting all of the operations
to the new subdivision surface implementation which ensures that
tangent space used to evaluate modifier and those operations is
exactly the same (before modifier will use new code and the operations
will still use an old one).

The next step is to get sculpting on a non-top level to work, and
that actually requires fixes in the undo system.

1 files changed, 302 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/multires_reshape.h b/source/blender/blenkernel/intern/multires_reshape.h
new file mode 100644
index 00000000000..6a51c1112cb
--- /dev/null
+++ b/source/blender/blenkernel/intern/multires_reshape.h
@@ -0,0 +1,302 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software  Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2020 Blender Foundation.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup bke
+ */
+
+#ifndef __BKE_INTERN_MULTIRES_RESHAPE_H__
+#define __BKE_INTERN_MULTIRES_RESHAPE_H__
+
+#include "BLI_sys_types.h"
+
+struct Depsgraph;
+struct GridPaintMask;
+struct MDisps;
+struct Mesh;
+struct MultiresModifierData;
+struct Object;
+struct Subdiv;
+struct SubdivCCG;
+
+typedef struct MultiresReshapeContext {
+  /* Base mesh from original object.
+   * NOTE: Does NOT include any leading modifiers in it. */
+  struct Mesh *base_mesh;
+
+  /* Subdivision surface created for multires modifier.
+   *
+   * The coarse mesh of this subdivision surface is a base mesh with all deformation modifiers
+   * leading multires applied on it. */
+  struct Subdiv *subdiv;
+  bool need_free_subdiv;
+
+  struct {
+    /* Level at which displacement is being assigned to.
+     * It will be propagated up from this level to top.level. */
+    int level;
+
+    /* Grid size for reshape.level. */
+    int grid_size;
+  } reshape;
+
+  struct {
+    /* Top level of the displacement grids.
+     * The displacement will be propagated up to this level. */
+    int level;
+
+    /* Grid size for top.level. */
+    int grid_size;
+  } top;
+
+  struct {
+    /* Copy of original displacement and painting masks. */
+    struct MDisps *mdisps;
+    struct GridPaintMask *grid_paint_masks;
+  } orig;
+
+  /* Number of grids which are required for base_mesh. */
+  int num_grids;
+
+  /* Destination displacement and mask.
+   * Points to a custom data on a destination mesh. */
+  struct MDisps *mdisps;
+  struct GridPaintMask *grid_paint_masks;
+
+  /* Indexed by face index, gives first grid index of the face. */
+  int *face_start_grid_index;
+
+  /* Indexed by grid index, contains face (poly) index in the base mesh from which the grid has
+   * been created (in other words, index of a poly which contains loop corresponding to the grid
+   * index). */
+  int *grid_to_face_index;
+
+  /* Indexed by ptex face index, gives first grid index of the ptex face.
+   *
+   * For non-quad base faces ptex face is created for every face corner, so it's similar to a
+   * grid in this case. In this case start grid index will be the only one for this ptex face.
+   *
+   * For quad base faces there is a single ptex face but 4 grids. So in this case there will be
+   * 4 grids for the ptex, starting at a value stored in this mapping. */
+  int *ptex_start_grid_index;
+
+  /* Indexed by base face index, returns first ptex face index corresponding
+   * to that base face. */
+  int *face_ptex_offset;
+} MultiresReshapeContext;
+
+/* Coordinate which identifies element of a grid.
+ * This is directly related on how CD_MDISPS stores dispalcement.
+ */
+typedef struct GridCoord {
+  int grid_index;
+  float u, v;
+} GridCoord;
+
+/* COordinate within ptex, which is what OpenSubdiv API operates on.  */
+typedef struct PTexCoord {
+  int ptex_face_index;
+  float u, v;
+} PTexCoord;
+
+/* Element of a grid data stored in the destination mesh.
+ * This is where reshaped coordinates and mask values will be written to. */
+typedef struct ReshapeGridElement {
+  float *displacement;
+  float *mask;
+} ReshapeGridElement;
+
+typedef struct ReshapeConstGridElement {
+  float displacement[3];
+  float mask;
+} ReshapeConstGridElement;
+
+/* ================================================================================================
+ * Construct/destruct reshape context.
+ */
+
+/* Create subdivision surface descriptor which is configured for surface evaluation at a given
+ * multires modifier. */
+struct Subdiv *multires_reshape_create_subdiv(struct Depsgraph *depsgraph,
+                                              struct Object *object,
+                                              const struct MultiresModifierData *mmd);
+
+bool multires_reshape_context_create_from_object(MultiresReshapeContext *reshape_context,
+                                                 struct Depsgraph *depsgraph,
+                                                 struct Object *object,
+                                                 struct MultiresModifierData *mmd);
+
+bool multires_reshape_context_create_from_ccg(MultiresReshapeContext *reshape_context,
+                                              struct SubdivCCG *subdiv_ccg,
+                                              struct Mesh *base_mesh,
+                                              int top_level);
+
+bool multires_reshape_context_create_from_subdivide(MultiresReshapeContext *reshape_context,
+                                                    struct Object *object,
+                                                    struct MultiresModifierData *mmd,
+                                                    int top_level);
+
+void multires_reshape_context_free(MultiresReshapeContext *reshape_context);
+
+/* ================================================================================================
+ * Helper accessors.
+ */
+
+/* For the given grid index get index of face it was created for. */
+int multires_reshape_grid_to_face_index(const MultiresReshapeContext *reshape_context,
+                                        int grid_index);
+
+/* For the given grid index get corner of a face it was created for. */
+int multires_reshape_grid_to_corner(const MultiresReshapeContext *reshape_context, int grid_index);
+
+bool multires_reshape_is_quad_face(const MultiresReshapeContext *reshape_context, int face_index);
+
+/* For the given grid index get index of corresponding ptex face. */
+int multires_reshape_grid_to_ptex_index(const MultiresReshapeContext *reshape_context,
+                                        int grid_index);
+
+/* Convert normalized coordinate within a grid to a normalized coordinate within a ptex face. */
+PTexCoord multires_reshape_grid_coord_to_ptex(const MultiresReshapeContext *reshape_context,
+                                              const GridCoord *grid_coord);
+
+/* Convert a normalized coordinate within a ptex face to a normalized coordinate within a grid. */
+GridCoord multires_reshape_ptex_coord_to_grid(const MultiresReshapeContext *reshape_context,
+                                              const PTexCoord *ptex_coord);
+
+/* Calculate tangent matrix which converts displacement to a object vector.
+ * Is calculated for the given surface derivatives at a given base face corner. */
+void multires_reshape_tangent_matrix_for_corner(const MultiresReshapeContext *reshape_context,
+                                                const int face_index,
+                                                const int corner,
+                                                const float dPdu[3],
+                                                const float dPdv[3],
+                                                float r_tangent_matrix[3][3]);
+
+/* Get grid elements which are to be reshaped at a given or ptex coordinate.
+ * The data is coming from final custom mdata layers. */
+ReshapeGridElement multires_reshape_grid_element_for_grid_coord(
+    const MultiresReshapeContext *reshape_context, const GridCoord *grid_coord);
+ReshapeGridElement multires_reshape_grid_element_for_ptex_coord(
+    const MultiresReshapeContext *reshape_context, const PTexCoord *ptex_coord);
+
+/* Get original grid element for the given coordinate. */
+ReshapeConstGridElement multires_reshape_orig_grid_element_for_grid_coord(
+    const MultiresReshapeContext *reshape_context, const GridCoord *grid_coord);
+
+/* ================================================================================================
+ * Sample limit surface of the base mesh.
+ */
+
+/* Evaluate limit surface created from base mesh.
+ * This is the limit surface which defines tangent space for MDisps. */
+void multires_reshape_evaluate_limit_at_grid(const MultiresReshapeContext *reshape_context,
+                                             const GridCoord *grid_coord,
+                                             float r_P[3],
+                                             float r_tangent_matrix[3][3]);
+
+/* ================================================================================================
+ * Custom data preparation.
+ */
+
+/* Make sure custom data is allocated for the given level. */
+void multires_reshape_ensure_grids(struct Mesh *mesh, const int level);
+
+/* ================================================================================================
+ * Functions specific to reshaping from a set of vertices in a object position.
+ */
+
+/* Returns truth if all coordinates were assigned.
+ *
+ * False will be returned if the number of vertex coordinates did not match required number of
+ * vertices at a reshape level. */
+bool multires_reshape_assign_final_coords_from_vertcos(
+    const MultiresReshapeContext *reshape_context,
+    const float (*vert_coords)[3],
+    const int num_vert_coords);
+
+/* ================================================================================================
+ * Functions specific to reshaping from CCG.
+ */
+
+/* NOTE: Displacement grids to be at least at a reshape level.
+ *
+ * Return truth if all coordinates have been updated. */
+bool multires_reshape_assign_final_coords_from_ccg(const MultiresReshapeContext *reshape_context,
+                                                   struct SubdivCCG *subdiv_ccg);
+
+/* ================================================================================================
+ * Functions specific to reshaping from MDISPS.
+ */
+
+/* Reads and writes to the current mesh CD_MDISPS. */
+void multires_reshape_assign_final_coords_from_mdisps(
+    const MultiresReshapeContext *reshape_context);
+
+/* Reads from original CD_MIDTSPS, writes to the current mesh CD_MDISPS. */
+void multires_reshape_assign_final_coords_from_orig_mdisps(
+    const MultiresReshapeContext *reshape_context);
+
+/* ================================================================================================
+ * Displacement smooth.
+ */
+
+/* Operates on a displacement grids (CD_MDISPS) which contains object space coordinates stopred for
+ * the reshape level.
+ *
+ * The result is grids which are defining mesh with a smooth surface and details starting from
+ * reshape level up to top level added back from original displacement grids. */
+void multires_reshape_smooth_object_grids_with_details(
+    const MultiresReshapeContext *reshape_context);
+
+/* Operates on a displacement grids (CD_MDISPS) which contains object spacecoordinates stopred for
+ * the reshape level.
+ *
+ * Makes it so surface on top level looks smooth. Details are not preserved
+ */
+void multires_reshape_smooth_object_grids(const MultiresReshapeContext *reshape_context);
+
+/* ================================================================================================
+ * Displacement, space conversion.
+ */
+
+/* Store original grid data, so then it's possible to calculate delta from it and add
+ * high-frequency content on top of reshaped grids. */
+void multires_reshape_store_original_grids(MultiresReshapeContext *reshape_context);
+
+void multires_reshape_object_grids_to_tangent_displacement(
+    const MultiresReshapeContext *reshape_context);
+
+/* ================================================================================================
+ * Apply base.
+ */
+
+/* Update mesh coordinates to the final positions of displacement in object space.
+ * This is effectively desired position of base mesh vertices after caneling out displacement.
+ *
+ * NOTE: Expects that mesh's CD_MDISPS has been set ot object space positions. */
+void multires_reshape_apply_base_update_mesh_coords(MultiresReshapeContext *reshape_context);
+
+/* Perform better fitting of the base mesh so its subdivided version brings vertices to their
+ * desired locations. */
+void multires_reshape_apply_base_refit_base_mesh(MultiresReshapeContext *reshape_context);
+
+/* Refine subdivision surface to the new positions of the base mesh. */
+void multires_reshape_apply_base_refine_subdiv(MultiresReshapeContext *reshape_context);
+
+#endif /* __BKE_INTERN_MULTIRES_RESHAPE_H__ */