Multires: Move current reshaping/propagation logic to legacy file

It will eventually rewritten.
This commit prepares some clean space to start this process.

So far no functional changes.

1 files changed, 1056 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/multires_reshape_legacy.c b/source/blender/blenkernel/intern/multires_reshape_legacy.c
new file mode 100644
index 00000000000..0a8248b25f1
--- /dev/null
+++ b/source/blender/blenkernel/intern/multires_reshape_legacy.c
@@ -0,0 +1,1056 @@
+/*
+ * 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) 2018 Blender Foundation.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup bke
+ */
+
+#include "MEM_guardedalloc.h"
+
+#include "DNA_mesh_types.h"
+#include "DNA_meshdata_types.h"
+#include "DNA_scene_types.h"
+
+#include "BLI_utildefines.h"
+#include "BLI_math_vector.h"
+#include "BLI_task.h"
+
+#include "BKE_ccg.h"
+#include "BKE_lib_id.h"
+#include "BKE_mesh.h"
+#include "BKE_mesh_runtime.h"
+#include "BKE_modifier.h"
+#include "BKE_multires.h"
+#include "BKE_subdiv.h"
+#include "BKE_subdiv_ccg.h"
+#include "BKE_subdiv_eval.h"
+#include "BKE_subdiv_foreach.h"
+#include "BKE_subdiv_mesh.h"
+
+#include "DEG_depsgraph_query.h"
+
+static void multires_reshape_init_mmd(MultiresModifierData *reshape_mmd,
+                                      const MultiresModifierData *mmd)
+{
+  *reshape_mmd = *mmd;
+}
+
+static void multires_reshape_init_mmd_top_level(MultiresModifierData *reshape_mmd,
+                                                const MultiresModifierData *mmd)
+{
+  *reshape_mmd = *mmd;
+  reshape_mmd->lvl = reshape_mmd->totlvl;
+}
+
+/* =============================================================================
+ * General reshape implementation, reused by all particular cases.
+ */
+
+typedef struct MultiresReshapeContext {
+  Subdiv *subdiv;
+  const Mesh *coarse_mesh;
+  MDisps *mdisps;
+  GridPaintMask *grid_paint_mask;
+  int top_grid_size;
+  int top_level;
+  /* Indexed by coarse face index, returns first ptex face index corresponding
+   * to that coarse face. */
+  int *face_ptex_offset;
+} MultiresReshapeContext;
+
+static void multires_reshape_allocate_displacement_grid(MDisps *displacement_grid, const int level)
+{
+  const int grid_size = BKE_subdiv_grid_size_from_level(level);
+  const int grid_area = grid_size * grid_size;
+  float(*disps)[3] = MEM_calloc_arrayN(grid_area, 3 * sizeof(float), "multires disps");
+  if (displacement_grid->disps != NULL) {
+    MEM_freeN(displacement_grid->disps);
+  }
+  displacement_grid->disps = disps;
+  displacement_grid->totdisp = grid_area;
+  displacement_grid->level = level;
+}
+
+static void multires_reshape_ensure_displacement_grid(MDisps *displacement_grid, const int level)
+{
+  if (displacement_grid->disps != NULL && displacement_grid->level == level) {
+    return;
+  }
+  multires_reshape_allocate_displacement_grid(displacement_grid, level);
+}
+
+static void multires_reshape_ensure_displacement_grids(Mesh *mesh, const int grid_level)
+{
+  const int num_grids = mesh->totloop;
+  MDisps *mdisps = CustomData_get_layer(&mesh->ldata, CD_MDISPS);
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    multires_reshape_ensure_displacement_grid(&mdisps[grid_index], grid_level);
+  }
+}
+
+static void multires_reshape_ensure_mask_grids(Mesh *mesh, const int grid_level)
+{
+  GridPaintMask *grid_paint_masks = CustomData_get_layer(&mesh->ldata, CD_GRID_PAINT_MASK);
+  if (grid_paint_masks == NULL) {
+    return;
+  }
+  const int num_grids = mesh->totloop;
+  const int grid_size = BKE_subdiv_grid_size_from_level(grid_level);
+  const int grid_area = grid_size * grid_size;
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    GridPaintMask *grid_paint_mask = &grid_paint_masks[grid_index];
+    if (grid_paint_mask->level == grid_level) {
+      continue;
+    }
+    grid_paint_mask->level = grid_level;
+    if (grid_paint_mask->data) {
+      MEM_freeN(grid_paint_mask->data);
+    }
+    grid_paint_mask->data = MEM_calloc_arrayN(grid_area, sizeof(float), "gpm.data");
+  }
+}
+
+static void multires_reshape_ensure_grids(Mesh *mesh, const int grid_level)
+{
+  multires_reshape_ensure_displacement_grids(mesh, grid_level);
+  multires_reshape_ensure_mask_grids(mesh, grid_level);
+}
+
+/* Convert normalized coordinate within a grid to a normalized coordinate within
+ * a ptex face. */
+static void multires_reshape_corner_coord_to_ptex(const MPoly *coarse_poly,
+                                                  const int corner,
+                                                  const float corner_u,
+                                                  const float corner_v,
+                                                  float *r_ptex_face_u,
+                                                  float *r_ptex_face_v)
+{
+  if (coarse_poly->totloop == 4) {
+    float grid_u, grid_v;
+    BKE_subdiv_ptex_face_uv_to_grid_uv(corner_u, corner_v, &grid_u, &grid_v);
+    BKE_subdiv_rotate_grid_to_quad(corner, grid_u, grid_v, r_ptex_face_u, r_ptex_face_v);
+  }
+  else {
+    *r_ptex_face_u = corner_u;
+    *r_ptex_face_v = corner_v;
+  }
+}
+
+/* NOTE: The tangent vectors are measured in ptex face normalized coordinates,
+ * which is different from grid tangent. */
+static void multires_reshape_sample_surface(Subdiv *subdiv,
+                                            const MPoly *coarse_poly,
+                                            const int corner,
+                                            const float corner_u,
+                                            const float corner_v,
+                                            const int ptex_face_index,
+                                            float r_P[3],
+                                            float r_dPdu[3],
+                                            float r_dPdv[3])
+{
+  float ptex_face_u, ptex_face_v;
+  multires_reshape_corner_coord_to_ptex(
+      coarse_poly, corner, corner_u, corner_v, &ptex_face_u, &ptex_face_v);
+  BKE_subdiv_eval_limit_point_and_derivatives(
+      subdiv, ptex_face_index, ptex_face_u, ptex_face_v, r_P, r_dPdu, r_dPdv);
+}
+
+static void multires_reshape_tangent_matrix_for_corner(const MPoly *coarse_poly,
+                                                       const int coarse_corner,
+                                                       const float dPdu[3],
+                                                       const float dPdv[3],
+                                                       float r_tangent_matrix[3][3])
+{
+  /* For a quad faces we would need to flip the tangent, since they will use
+   * use different coordinates within displacement grid comparent to ptex
+   * face. */
+  const bool is_quad = (coarse_poly->totloop == 4);
+  const int tangent_corner = is_quad ? coarse_corner : 0;
+  BKE_multires_construct_tangent_matrix(r_tangent_matrix, dPdu, dPdv, tangent_corner);
+}
+
+static void multires_reshape_vertex_from_final_data(MultiresReshapeContext *ctx,
+                                                    const int ptex_face_index,
+                                                    const float corner_u,
+                                                    const float corner_v,
+                                                    const int coarse_poly_index,
+                                                    const int coarse_corner,
+                                                    const float final_P[3],
+                                                    const float final_mask)
+{
+  Subdiv *subdiv = ctx->subdiv;
+  const int grid_size = ctx->top_grid_size;
+  const Mesh *coarse_mesh = ctx->coarse_mesh;
+  const MPoly *coarse_mpoly = coarse_mesh->mpoly;
+  const MPoly *coarse_poly = &coarse_mpoly[coarse_poly_index];
+  const int loop_index = coarse_poly->loopstart + coarse_corner;
+  /* Evaluate limit surface. */
+  float P[3], dPdu[3], dPdv[3];
+  multires_reshape_sample_surface(
+      subdiv, coarse_poly, coarse_corner, corner_u, corner_v, ptex_face_index, P, dPdu, dPdv);
+  /* Construct tangent matrix which matches orientation of the current
+   * displacement grid. */
+  float tangent_matrix[3][3], inv_tangent_matrix[3][3];
+  multires_reshape_tangent_matrix_for_corner(
+      coarse_poly, coarse_corner, dPdu, dPdv, tangent_matrix);
+  invert_m3_m3(inv_tangent_matrix, tangent_matrix);
+  /* Convert object coordinate to a tangent space of displacement grid. */
+  float D[3];
+  sub_v3_v3v3(D, final_P, P);
+  float tangent_D[3];
+  mul_v3_m3v3(tangent_D, inv_tangent_matrix, D);
+  /* Calculate index of element within the grid. */
+  float grid_u, grid_v;
+  BKE_subdiv_ptex_face_uv_to_grid_uv(corner_u, corner_v, &grid_u, &grid_v);
+  const int grid_x = (grid_u * (grid_size - 1) + 0.5f);
+  const int grid_y = (grid_v * (grid_size - 1) + 0.5f);
+  const int index = grid_y * grid_size + grid_x;
+  /* Write tangent displacement. */
+  MDisps *displacement_grid = &ctx->mdisps[loop_index];
+  copy_v3_v3(displacement_grid->disps[index], tangent_D);
+  /* Write mask grid. */
+  if (ctx->grid_paint_mask != NULL) {
+    GridPaintMask *grid_paint_mask = &ctx->grid_paint_mask[loop_index];
+    BLI_assert(grid_paint_mask->level == displacement_grid->level);
+    grid_paint_mask->data[index] = final_mask;
+  }
+}
+
+/* =============================================================================
+ * Helpers to propagate displacement to higher levels.
+ */
+
+typedef struct MultiresPropagateData {
+  /* Number of displacement grids. */
+  int num_grids;
+  /* Resolution level up to which displacement is known. */
+  int reshape_level;
+  /* Resolution up to which propagation is happening, affecting all the
+   * levels in [reshape_level + 1, top_level]. */
+  int top_level;
+  /* Grid sizes at the corresponding levels. */
+  int reshape_grid_size;
+  int top_grid_size;
+  /* Keys to access CCG at different levels. */
+  CCGKey reshape_level_key;
+  CCGKey top_level_key;
+  /* Original grid data, before any updates for reshape.
+   * Contains data at the reshape_level resolution level. */
+  CCGElem **orig_grids_data;
+  /* Custom data layers from a coarse mesh. */
+  MDisps *mdisps;
+  GridPaintMask *grid_paint_mask;
+} MultiresPropagateData;
+
+static CCGElem **allocate_grids(CCGKey *key, int num_grids)
+{
+  CCGElem **grids = MEM_calloc_arrayN(num_grids, sizeof(CCGElem *), "reshape grids*");
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    grids[grid_index] = MEM_calloc_arrayN(
+        key->elem_size, key->grid_area, "reshape orig_grids_data elems");
+  }
+  return grids;
+}
+
+static void free_grids(CCGElem **grids, int num_grids)
+{
+  if (grids == NULL) {
+    return;
+  }
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    MEM_freeN(grids[grid_index]);
+  }
+  MEM_freeN(grids);
+}
+
+/* Initialize element sizes and offsets. */
+static void multires_reshape_init_key_layers(CCGKey *key, const MultiresPropagateData *data)
+{
+  key->elem_size = 3 * sizeof(float);
+  if (data->grid_paint_mask != NULL) {
+    key->mask_offset = 3 * sizeof(float);
+    key->elem_size += sizeof(float);
+    key->has_mask = true;
+  }
+  else {
+    key->mask_offset = -1;
+    key->has_mask = false;
+  }
+  /* We never have normals in original grids. */
+  key->normal_offset = -1;
+  key->has_normals = false;
+}
+
+/* Initialize key used to access reshape grids at given level. */
+static void multires_reshape_init_level_key(CCGKey *key,
+                                            const MultiresPropagateData *data,
+                                            const int level)
+{
+  key->level = level;
+  /* Init layers. */
+  multires_reshape_init_key_layers(key, data);
+  /* By default, only 3 floats for coordinate, */
+  key->grid_size = BKE_subdiv_grid_size_from_level(key->level);
+  key->grid_area = key->grid_size * key->grid_size;
+  key->grid_bytes = key->elem_size * key->grid_area;
+}
+
+static void multires_reshape_store_original_grids(MultiresPropagateData *data)
+{
+  const int num_grids = data->num_grids;
+  /* Original data to be backed up. */
+  const MDisps *mdisps = data->mdisps;
+  const GridPaintMask *grid_paint_mask = data->grid_paint_mask;
+  /* Allocate grids for backup. */
+  CCGKey *orig_key = &data->reshape_level_key;
+  CCGElem **orig_grids_data = allocate_grids(orig_key, num_grids);
+  /* Fill in grids. */
+  const int orig_grid_size = data->reshape_grid_size;
+  const int top_grid_size = data->top_grid_size;
+  const int skip = (top_grid_size - 1) / (orig_grid_size - 1);
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    CCGElem *orig_grid = orig_grids_data[grid_index];
+    for (int y = 0; y < orig_grid_size; y++) {
+      const int top_y = y * skip;
+      for (int x = 0; x < orig_grid_size; x++) {
+        const int top_x = x * skip;
+        const int top_index = top_y * top_grid_size + top_x;
+        memcpy(CCG_grid_elem_co(orig_key, orig_grid, x, y),
+               mdisps[grid_index].disps[top_index],
+               sizeof(float) * 3);
+        if (orig_key->has_mask) {
+          *CCG_grid_elem_mask(
+              orig_key, orig_grid, x, y) = grid_paint_mask[grid_index].data[top_index];
+        }
+      }
+    }
+  }
+  /* Store in the context. */
+  data->orig_grids_data = orig_grids_data;
+}
+
+static void multires_reshape_propagate_prepare(MultiresPropagateData *data,
+                                               Mesh *coarse_mesh,
+                                               const int reshape_level,
+                                               const int top_level)
+{
+  BLI_assert(reshape_level <= top_level);
+  memset(data, 0, sizeof(*data));
+  data->num_grids = coarse_mesh->totloop;
+  data->reshape_level = reshape_level;
+  data->top_level = top_level;
+  if (reshape_level == top_level) {
+    /* Nothing to do, reshape will happen on the whole grid content. */
+    return;
+  }
+  data->mdisps = CustomData_get_layer(&coarse_mesh->ldata, CD_MDISPS);
+  data->grid_paint_mask = CustomData_get_layer(&coarse_mesh->ldata, CD_GRID_PAINT_MASK);
+  data->top_grid_size = BKE_subdiv_grid_size_from_level(top_level);
+  data->reshape_grid_size = BKE_subdiv_grid_size_from_level(reshape_level);
+  /* Initialize keys to access CCG at different levels. */
+  multires_reshape_init_level_key(&data->reshape_level_key, data, data->reshape_level);
+  multires_reshape_init_level_key(&data->top_level_key, data, data->top_level);
+  /* Make a copy of grids before reshaping, so we can calculate deltas
+   * later on. */
+  multires_reshape_store_original_grids(data);
+}
+
+static void multires_reshape_propagate_prepare_from_mmd(MultiresPropagateData *data,
+                                                        struct Depsgraph *depsgraph,
+                                                        Object *object,
+                                                        const MultiresModifierData *mmd,
+                                                        const int top_level,
+                                                        const bool use_render_params)
+{
+  /* TODO(sergey): Find mode reliable way of getting current level. */
+  Scene *scene_eval = DEG_get_evaluated_scene(depsgraph);
+  Mesh *mesh = object->data;
+  const int level = multires_get_level(scene_eval, object, mmd, use_render_params, true);
+  multires_reshape_propagate_prepare(data, mesh, level, top_level);
+}
+
+/* Calculate delta of changed reshape level data layers. Delta goes to a
+ * grids at top level (meaning, the result grids are only partially filled
+ * in). */
+static void multires_reshape_calculate_delta(MultiresPropagateData *data,
+                                             CCGElem **delta_grids_data)
+{
+  const int num_grids = data->num_grids;
+  /* At this point those custom data layers has updated data for the
+   * level we are propagating from. */
+  const MDisps *mdisps = data->mdisps;
+  const GridPaintMask *grid_paint_mask = data->grid_paint_mask;
+  CCGKey *reshape_key = &data->reshape_level_key;
+  CCGKey *delta_level_key = &data->top_level_key;
+  /* Calculate delta. */
+  const int top_grid_size = data->top_grid_size;
+  const int reshape_grid_size = data->reshape_grid_size;
+  const int delta_grid_size = data->top_grid_size;
+  const int skip = (top_grid_size - 1) / (reshape_grid_size - 1);
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    /*const*/ CCGElem *orig_grid = data->orig_grids_data[grid_index];
+    CCGElem *delta_grid = delta_grids_data[grid_index];
+    for (int y = 0; y < reshape_grid_size; y++) {
+      const int top_y = y * skip;
+      for (int x = 0; x < reshape_grid_size; x++) {
+        const int top_x = x * skip;
+        const int top_index = top_y * delta_grid_size + top_x;
+        sub_v3_v3v3(CCG_grid_elem_co(delta_level_key, delta_grid, top_x, top_y),
+                    mdisps[grid_index].disps[top_index],
+                    CCG_grid_elem_co(reshape_key, orig_grid, x, y));
+        if (delta_level_key->has_mask) {
+          const float old_mask_value = *CCG_grid_elem_mask(reshape_key, orig_grid, x, y);
+          const float new_mask_value = grid_paint_mask[grid_index].data[top_index];
+          *CCG_grid_elem_mask(delta_level_key, delta_grid, top_x, top_y) = new_mask_value -
+                                                                           old_mask_value;
+        }
+      }
+    }
+  }
+}
+
+/* Makes it so delta is propagated onto all the higher levels, but is also
+ * that this delta is smoothed in a way that it does not cause artifacts on
+ * boundaries. */
+
+typedef struct MultiresPropagateCornerData {
+  float coord_delta[3];
+  float mask_delta;
+} MultiresPropagateCornerData;
+
+BLI_INLINE void multires_reshape_propagate_init_patch_corners(
+    MultiresPropagateData *data,
+    CCGElem *delta_grid,
+    const int patch_x,
+    const int patch_y,
+    MultiresPropagateCornerData r_corners[4])
+{
+  CCGKey *delta_level_key = &data->top_level_key;
+  const int orig_grid_size = data->reshape_grid_size;
+  const int top_grid_size = data->top_grid_size;
+  const int skip = (top_grid_size - 1) / (orig_grid_size - 1);
+  const int x = patch_x * skip;
+  const int y = patch_y * skip;
+  /* Store coordinate deltas. */
+  copy_v3_v3(r_corners[0].coord_delta, CCG_grid_elem_co(delta_level_key, delta_grid, x, y));
+  copy_v3_v3(r_corners[1].coord_delta, CCG_grid_elem_co(delta_level_key, delta_grid, x + skip, y));
+  copy_v3_v3(r_corners[2].coord_delta, CCG_grid_elem_co(delta_level_key, delta_grid, x, y + skip));
+  copy_v3_v3(r_corners[3].coord_delta,
+             CCG_grid_elem_co(delta_level_key, delta_grid, x + skip, y + skip));
+  if (delta_level_key->has_mask) {
+    r_corners[0].mask_delta = *CCG_grid_elem_mask(delta_level_key, delta_grid, x, y);
+    r_corners[1].mask_delta = *CCG_grid_elem_mask(delta_level_key, delta_grid, x + skip, y);
+    r_corners[2].mask_delta = *CCG_grid_elem_mask(delta_level_key, delta_grid, x, y + skip);
+    r_corners[3].mask_delta = *CCG_grid_elem_mask(delta_level_key, delta_grid, x + skip, y + skip);
+  }
+}
+
+BLI_INLINE void multires_reshape_propagate_interpolate_coord(
+    float delta[3], const MultiresPropagateCornerData corners[4], const float weights[4])
+{
+  interp_v3_v3v3v3v3(delta,
+                     corners[0].coord_delta,
+                     corners[1].coord_delta,
+                     corners[2].coord_delta,
+                     corners[3].coord_delta,
+                     weights);
+}
+
+BLI_INLINE float multires_reshape_propagate_interpolate_mask(
+    const MultiresPropagateCornerData corners[4], const float weights[4])
+{
+  return corners[0].mask_delta * weights[0] + corners[1].mask_delta * weights[1] +
+         corners[2].mask_delta * weights[2] + corners[3].mask_delta * weights[3];
+}
+
+BLI_INLINE void multires_reshape_propagate_and_smooth_delta_grid_patch(MultiresPropagateData *data,
+                                                                       CCGElem *delta_grid,
+                                                                       const int patch_x,
+                                                                       const int patch_y)
+{
+  CCGKey *delta_level_key = &data->top_level_key;
+  const int orig_grid_size = data->reshape_grid_size;
+  const int top_grid_size = data->top_grid_size;
+  const int skip = (top_grid_size - 1) / (orig_grid_size - 1);
+  const float skip_inv = 1.0f / (float)skip;
+  MultiresPropagateCornerData corners[4];
+  multires_reshape_propagate_init_patch_corners(data, delta_grid, patch_x, patch_y, corners);
+  const int start_x = patch_x * skip;
+  const int start_y = patch_y * skip;
+  for (int y = 0; y <= skip; y++) {
+    const float v = (float)y * skip_inv;
+    const int final_y = start_y + y;
+    for (int x = 0; x <= skip; x++) {
+      const float u = (float)x * skip_inv;
+      const int final_x = start_x + x;
+      const float linear_weights[4] = {
+          (1.0f - u) * (1.0f - v), u * (1.0f - v), (1.0f - u) * v, u * v};
+      multires_reshape_propagate_interpolate_coord(
+          CCG_grid_elem_co(delta_level_key, delta_grid, final_x, final_y),
+          corners,
+          linear_weights);
+      if (delta_level_key->has_mask) {
+        float *mask = CCG_grid_elem_mask(delta_level_key, delta_grid, final_x, final_y);
+        *mask = multires_reshape_propagate_interpolate_mask(corners, linear_weights);
+      }
+    }
+  }
+}
+
+BLI_INLINE void multires_reshape_propagate_and_smooth_delta_grid(MultiresPropagateData *data,
+                                                                 CCGElem *delta_grid)
+{
+  const int orig_grid_size = data->reshape_grid_size;
+  for (int patch_y = 0; patch_y < orig_grid_size - 1; patch_y++) {
+    for (int patch_x = 0; patch_x < orig_grid_size - 1; patch_x++) {
+      multires_reshape_propagate_and_smooth_delta_grid_patch(data, delta_grid, patch_x, patch_y);
+    }
+  }
+}
+
+/* Entry point to propagate+smooth. */
+static void multires_reshape_propagate_and_smooth_delta(MultiresPropagateData *data,
+                                                        CCGElem **delta_grids_data)
+{
+  const int num_grids = data->num_grids;
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    CCGElem *delta_grid = delta_grids_data[grid_index];
+    multires_reshape_propagate_and_smooth_delta_grid(data, delta_grid);
+  }
+}
+
+/* Apply smoothed deltas on the actual data layers. */
+static void multires_reshape_propagate_apply_delta(MultiresPropagateData *data,
+                                                   CCGElem **delta_grids_data)
+{
+  const int num_grids = data->num_grids;
+  /* At this point those custom data layers has updated data for the
+   * level we are propagating from. */
+  MDisps *mdisps = data->mdisps;
+  GridPaintMask *grid_paint_mask = data->grid_paint_mask;
+  CCGKey *orig_key = &data->reshape_level_key;
+  CCGKey *delta_level_key = &data->top_level_key;
+  CCGElem **orig_grids_data = data->orig_grids_data;
+  const int orig_grid_size = data->reshape_grid_size;
+  const int top_grid_size = data->top_grid_size;
+  const int skip = (top_grid_size - 1) / (orig_grid_size - 1);
+  /* Restore grid values at the reshape level. Those values are to be changed
+   * to the accommodate for the smooth delta. */
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    CCGElem *orig_grid = orig_grids_data[grid_index];
+    for (int y = 0; y < orig_grid_size; y++) {
+      const int top_y = y * skip;
+      for (int x = 0; x < orig_grid_size; x++) {
+        const int top_x = x * skip;
+        const int top_index = top_y * top_grid_size + top_x;
+        copy_v3_v3(mdisps[grid_index].disps[top_index],
+                   CCG_grid_elem_co(orig_key, orig_grid, x, y));
+        if (grid_paint_mask != NULL) {
+          grid_paint_mask[grid_index].data[top_index] = *CCG_grid_elem_mask(
+              orig_key, orig_grid, x, y);
+        }
+      }
+    }
+  }
+  /* Add smoothed delta to all the levels. */
+  for (int grid_index = 0; grid_index < num_grids; grid_index++) {
+    CCGElem *delta_grid = delta_grids_data[grid_index];
+    for (int y = 0; y < top_grid_size; y++) {
+      for (int x = 0; x < top_grid_size; x++) {
+        const int top_index = y * top_grid_size + x;
+        add_v3_v3(mdisps[grid_index].disps[top_index],
+                  CCG_grid_elem_co(delta_level_key, delta_grid, x, y));
+        if (delta_level_key->has_mask) {
+          grid_paint_mask[grid_index].data[top_index] += *CCG_grid_elem_mask(
+              delta_level_key, delta_grid, x, y);
+        }
+      }
+    }
+  }
+}
+
+static void multires_reshape_propagate(MultiresPropagateData *data)
+{
+  if (data->reshape_level == data->top_level) {
+    return;
+  }
+  const int num_grids = data->num_grids;
+  /* Calculate delta made at the reshape level. */
+  CCGKey *delta_level_key = &data->top_level_key;
+  CCGElem **delta_grids_data = allocate_grids(delta_level_key, num_grids);
+  multires_reshape_calculate_delta(data, delta_grids_data);
+  /* Propagate deltas to the higher levels. */
+  multires_reshape_propagate_and_smooth_delta(data, delta_grids_data);
+  /* Finally, apply smoothed deltas. */
+  multires_reshape_propagate_apply_delta(data, delta_grids_data);
+  /* Cleanup. */
+  free_grids(delta_grids_data, num_grids);
+}
+
+static void multires_reshape_propagate_free(MultiresPropagateData *data)
+{
+  free_grids(data->orig_grids_data, data->num_grids);
+}
+
+/* =============================================================================
+ * Reshape from deformed vertex coordinates.
+ */
+
+typedef struct MultiresReshapeFromDeformedVertsContext {
+  MultiresReshapeContext reshape_ctx;
+  const float (*deformed_verts)[3];
+  int num_deformed_verts;
+} MultiresReshapeFromDeformedVertsContext;
+
+static bool multires_reshape_topology_info(const SubdivForeachContext *foreach_context,
+                                           const int num_vertices,
+                                           const int UNUSED(num_edges),
+                                           const int UNUSED(num_loops),
+                                           const int UNUSED(num_polygons))
+{
+  MultiresReshapeFromDeformedVertsContext *ctx = foreach_context->user_data;
+  if (num_vertices != ctx->num_deformed_verts) {
+    return false;
+  }
+  return true;
+}
+
+/* Will run reshaping for all grid elements which are adjacent to the given
+ * one. This is the way to ensure continuity of displacement stored in the
+ * grids across the inner boundaries of the grids. */
+static void multires_reshape_neighour_boundary_vertices(MultiresReshapeContext *ctx,
+                                                        const int UNUSED(ptex_face_index),
+                                                        const float corner_u,
+                                                        const float corner_v,
+                                                        const int coarse_poly_index,
+                                                        const int coarse_corner,
+                                                        const float final_P[3],
+                                                        const float final_mask)
+{
+  const Mesh *coarse_mesh = ctx->coarse_mesh;
+  const MPoly *coarse_mpoly = coarse_mesh->mpoly;
+  const MPoly *coarse_poly = &coarse_mpoly[coarse_poly_index];
+  const int num_corners = coarse_poly->totloop;
+  const int start_ptex_face_index = ctx->face_ptex_offset[coarse_poly_index];
+  const bool is_quad = (coarse_poly->totloop == 4);
+  if (corner_u == 1.0f && corner_v == 1.0f) {
+    for (int current_corner = 0; current_corner < num_corners; current_corner++) {
+      if (current_corner == coarse_corner) {
+        continue;
+      }
+      const int current_ptex_face_index = is_quad ? start_ptex_face_index :
+                                                    start_ptex_face_index + current_corner;
+      multires_reshape_vertex_from_final_data(ctx,
+                                              current_ptex_face_index,
+                                              1.0f,
+                                              1.0f,
+                                              coarse_poly_index,
+                                              current_corner,
+                                              final_P,
+                                              final_mask);
+    }
+  }
+  else if (corner_u == 1.0f) {
+    const float next_corner_index = (coarse_corner + 1) % num_corners;
+    const float next_corner_u = corner_v;
+    const float next_corner_v = 1.0f;
+    const int next_ptex_face_index = is_quad ? start_ptex_face_index :
+                                               start_ptex_face_index + next_corner_index;
+    multires_reshape_vertex_from_final_data(ctx,
+                                            next_ptex_face_index,
+                                            next_corner_u,
+                                            next_corner_v,
+                                            coarse_poly_index,
+                                            next_corner_index,
+                                            final_P,
+                                            final_mask);
+  }
+  else if (corner_v == 1.0f) {
+    const float prev_corner_index = (coarse_corner + num_corners - 1) % num_corners;
+    const float prev_corner_u = 1.0f;
+    const float prev_corner_v = corner_u;
+    const int prev_ptex_face_index = is_quad ? start_ptex_face_index :
+                                               start_ptex_face_index + prev_corner_index;
+    multires_reshape_vertex_from_final_data(ctx,
+                                            prev_ptex_face_index,
+                                            prev_corner_u,
+                                            prev_corner_v,
+                                            coarse_poly_index,
+                                            prev_corner_index,
+                                            final_P,
+                                            final_mask);
+  }
+}
+
+static void multires_reshape_vertex(MultiresReshapeFromDeformedVertsContext *ctx,
+                                    const int ptex_face_index,
+                                    const float u,
+                                    const float v,
+                                    const int coarse_poly_index,
+                                    const int coarse_corner,
+                                    const int subdiv_vertex_index)
+{
+  const float *final_P = ctx->deformed_verts[subdiv_vertex_index];
+  const Mesh *coarse_mesh = ctx->reshape_ctx.coarse_mesh;
+  const MPoly *coarse_mpoly = coarse_mesh->mpoly;
+  const MPoly *coarse_poly = &coarse_mpoly[coarse_poly_index];
+  const bool is_quad = (coarse_poly->totloop == 4);
+  float corner_u, corner_v;
+  int actual_coarse_corner;
+  if (is_quad) {
+    actual_coarse_corner = BKE_subdiv_rotate_quad_to_corner(u, v, &corner_u, &corner_v);
+  }
+  else {
+    actual_coarse_corner = coarse_corner;
+    corner_u = u;
+    corner_v = v;
+  }
+  multires_reshape_vertex_from_final_data(&ctx->reshape_ctx,
+                                          ptex_face_index,
+                                          corner_u,
+                                          corner_v,
+                                          coarse_poly_index,
+                                          actual_coarse_corner,
+                                          final_P,
+                                          0.0f);
+  multires_reshape_neighour_boundary_vertices(&ctx->reshape_ctx,
+                                              ptex_face_index,
+                                              corner_u,
+                                              corner_v,
+                                              coarse_poly_index,
+                                              actual_coarse_corner,
+                                              final_P,
+                                              0.0f);
+}
+
+static void multires_reshape_vertex_inner(const SubdivForeachContext *foreach_context,
+                                          void *UNUSED(tls_v),
+                                          const int ptex_face_index,
+                                          const float u,
+                                          const float v,
+                                          const int coarse_poly_index,
+                                          const int coarse_corner,
+                                          const int subdiv_vertex_index)
+{
+  MultiresReshapeFromDeformedVertsContext *ctx = foreach_context->user_data;
+  multires_reshape_vertex(
+      ctx, ptex_face_index, u, v, coarse_poly_index, coarse_corner, subdiv_vertex_index);
+}
+
+static void multires_reshape_vertex_every_corner(
+    const struct SubdivForeachContext *foreach_context,
+    void *UNUSED(tls_v),
+    const int ptex_face_index,
+    const float u,
+    const float v,
+    const int UNUSED(coarse_vertex_index),
+    const int coarse_poly_index,
+    const int coarse_corner,
+    const int subdiv_vertex_index)
+{
+  MultiresReshapeFromDeformedVertsContext *ctx = foreach_context->user_data;
+  multires_reshape_vertex(
+      ctx, ptex_face_index, u, v, coarse_poly_index, coarse_corner, subdiv_vertex_index);
+}
+
+static void multires_reshape_vertex_every_edge(const struct SubdivForeachContext *foreach_context,
+                                               void *UNUSED(tls_v),
+                                               const int ptex_face_index,
+                                               const float u,
+                                               const float v,
+                                               const int UNUSED(coarse_edge_index),
+                                               const int coarse_poly_index,
+                                               const int coarse_corner,
+                                               const int subdiv_vertex_index)
+{
+  MultiresReshapeFromDeformedVertsContext *ctx = foreach_context->user_data;
+  multires_reshape_vertex(
+      ctx, ptex_face_index, u, v, coarse_poly_index, coarse_corner, subdiv_vertex_index);
+}
+
+static Subdiv *multires_create_subdiv_for_reshape(struct Depsgraph *depsgraph,
+                                                  /*const*/ Object *object,
+                                                  const MultiresModifierData *mmd)
+{
+  Scene *scene_eval = DEG_get_evaluated_scene(depsgraph);
+  Object *object_eval = DEG_get_evaluated_object(depsgraph, object);
+  Mesh *deformed_mesh = mesh_get_eval_deform(
+      depsgraph, scene_eval, object_eval, &CD_MASK_BAREMESH);
+  SubdivSettings subdiv_settings;
+  BKE_multires_subdiv_settings_init(&subdiv_settings, mmd);
+  Subdiv *subdiv = BKE_subdiv_new_from_mesh(&subdiv_settings, deformed_mesh);
+  if (!BKE_subdiv_eval_update_from_mesh(subdiv, deformed_mesh, NULL)) {
+    BKE_subdiv_free(subdiv);
+    return NULL;
+  }
+  return subdiv;
+}
+
+static bool multires_reshape_from_vertcos(struct Depsgraph *depsgraph,
+                                          Object *object,
+                                          const MultiresModifierData *mmd,
+                                          const float (*deformed_verts)[3],
+                                          const int num_deformed_verts,
+                                          const bool use_render_params)
+{
+  Scene *scene_eval = DEG_get_evaluated_scene(depsgraph);
+  Mesh *coarse_mesh = object->data;
+  MDisps *mdisps = CustomData_get_layer(&coarse_mesh->ldata, CD_MDISPS);
+  /* Pick maximum between multires level and displacement level.
+   * This is because mesh can be used by objects with multires at different
+   * levels.
+   *
+   * TODO(sergey): At this point it should be possible to always use
+   * mdisps->level. */
+  const int top_level = max_ii(mmd->totlvl, mdisps->level);
+  /* Make sure displacement grids are ready. */
+  multires_reshape_ensure_grids(coarse_mesh, top_level);
+  /* Initialize subdivision surface. */
+  Subdiv *subdiv = multires_create_subdiv_for_reshape(depsgraph, object, mmd);
+  if (subdiv == NULL) {
+    return false;
+  }
+  /* Construct context. */
+  MultiresReshapeFromDeformedVertsContext reshape_deformed_verts_ctx = {
+      .reshape_ctx =
+          {
+              .subdiv = subdiv,
+              .coarse_mesh = coarse_mesh,
+              .mdisps = mdisps,
+              .grid_paint_mask = NULL,
+              .top_grid_size = BKE_subdiv_grid_size_from_level(top_level),
+              .top_level = top_level,
+              .face_ptex_offset = BKE_subdiv_face_ptex_offset_get(subdiv),
+          },
+      .deformed_verts = deformed_verts,
+      .num_deformed_verts = num_deformed_verts,
+  };
+  SubdivForeachContext foreach_context = {
+      .topology_info = multires_reshape_topology_info,
+      .vertex_inner = multires_reshape_vertex_inner,
+      .vertex_every_edge = multires_reshape_vertex_every_edge,
+      .vertex_every_corner = multires_reshape_vertex_every_corner,
+      .user_data = &reshape_deformed_verts_ctx,
+  };
+  /* Initialize mesh rasterization settings. */
+  SubdivToMeshSettings mesh_settings;
+  BKE_multires_subdiv_mesh_settings_init(
+      &mesh_settings, scene_eval, object, mmd, use_render_params, true);
+  /* Initialize propagation to higher levels. */
+  MultiresPropagateData propagate_data;
+  multires_reshape_propagate_prepare_from_mmd(
+      &propagate_data, depsgraph, object, mmd, top_level, use_render_params);
+  /* Run all the callbacks. */
+  BKE_subdiv_foreach_subdiv_geometry(subdiv, &foreach_context, &mesh_settings, coarse_mesh);
+  BKE_subdiv_free(subdiv);
+  /* Update higher levels if needed. */
+  multires_reshape_propagate(&propagate_data);
+  multires_reshape_propagate_free(&propagate_data);
+  return true;
+}
+
+/* =============================================================================
+ * Reshape from object.
+ */
+
+/* Returns truth on success, false otherwise.
+ *
+ * This function might fail in cases like source and destination not having
+ * matched amount of vertices. */
+bool multiresModifier_reshapeFromObject(struct Depsgraph *depsgraph,
+                                        MultiresModifierData *mmd,
+                                        Object *dst,
+                                        Object *src)
+{
+  /* Would be cool to support this eventually, but it is very tricky to match
+   * vertices order even for meshes, when mixing meshes and other objects it's
+   * even more tricky. */
+  if (src->type != OB_MESH) {
+    return false;
+  }
+  MultiresModifierData reshape_mmd;
+  multires_reshape_init_mmd(&reshape_mmd, mmd);
+  /* Get evaluated vertices locations to reshape to. */
+  Scene *scene_eval = DEG_get_evaluated_scene(depsgraph);
+  Object *src_eval = DEG_get_evaluated_object(depsgraph, src);
+  Mesh *src_mesh_eval = mesh_get_eval_final(depsgraph, scene_eval, src_eval, &CD_MASK_BAREMESH);
+  int num_deformed_verts;
+  float(*deformed_verts)[3] = BKE_mesh_vert_coords_alloc(src_mesh_eval, &num_deformed_verts);
+  bool result = multires_reshape_from_vertcos(
+      depsgraph, dst, &reshape_mmd, deformed_verts, num_deformed_verts, false);
+  MEM_freeN(deformed_verts);
+  return result;
+}
+
+/* =============================================================================
+ * Reshape from modifier.
+ */
+
+bool multiresModifier_reshapeFromDeformModifier(struct Depsgraph *depsgraph,
+                                                MultiresModifierData *mmd,
+                                                Object *object,
+                                                ModifierData *md)
+{
+  MultiresModifierData highest_mmd;
+  /* It is possible that the current subdivision level of multires is lower
+   * that it's maximum possible one (i.e., viewport is set to a lower level
+   * for the performance purposes). But even then, we want all the multires
+   * levels to be reshaped. Most accurate way to do so is to ignore all
+   * simplifications and calculate deformation modifier for the highest
+   * possible multires level.
+   * Alternative would be propagate displacement from current level to a
+   * higher ones, but that is likely to cause artifacts. */
+  multires_reshape_init_mmd_top_level(&highest_mmd, mmd);
+  Scene *scene_eval = DEG_get_evaluated_scene(depsgraph);
+  /* Perform sanity checks and early output. */
+  if (multires_get_level(scene_eval, object, &highest_mmd, false, true) == 0) {
+    return false;
+  }
+  /* Create mesh for the multires, ignoring any further modifiers (leading
+   * deformation modifiers will be applied though). */
+  Mesh *multires_mesh = BKE_multires_create_mesh(depsgraph, scene_eval, &highest_mmd, object);
+  int num_deformed_verts;
+  float(*deformed_verts)[3] = BKE_mesh_vert_coords_alloc(multires_mesh, &num_deformed_verts);
+  /* Apply deformation modifier on the multires, */
+  const ModifierEvalContext modifier_ctx = {
+      .depsgraph = depsgraph,
+      .object = object,
+      .flag = MOD_APPLY_USECACHE | MOD_APPLY_IGNORE_SIMPLIFY,
+  };
+  modwrap_deformVerts(md, &modifier_ctx, multires_mesh, deformed_verts, multires_mesh->totvert);
+  BKE_id_free(NULL, multires_mesh);
+  /* Reshaping */
+  bool result = multires_reshape_from_vertcos(
+      depsgraph, object, &highest_mmd, deformed_verts, num_deformed_verts, false);
+  /* Cleanup */
+  MEM_freeN(deformed_verts);
+  return result;
+}
+
+/* =============================================================================
+ * Reshape from grids.
+ */
+
+typedef struct ReshapeFromCCGTaskData {
+  MultiresReshapeContext reshape_ctx;
+  const CCGKey *key;
+  /*const*/ CCGElem **grids;
+} ReshapeFromCCGTaskData;
+
+static void reshape_from_ccg_task(void *__restrict userdata,
+                                  const int coarse_poly_index,
+                                  const TaskParallelTLS *__restrict UNUSED(tls))
+{
+  ReshapeFromCCGTaskData *data = userdata;
+  const CCGKey *key = data->key;
+  /*const*/ CCGElem **grids = data->grids;
+  const Mesh *coarse_mesh = data->reshape_ctx.coarse_mesh;
+  const MPoly *coarse_mpoly = coarse_mesh->mpoly;
+  const MPoly *coarse_poly = &coarse_mpoly[coarse_poly_index];
+  const int key_grid_size = key->grid_size;
+  const int key_grid_size_1 = key_grid_size - 1;
+  const int resolution = key_grid_size;
+  const float resolution_1_inv = 1.0f / (float)(resolution - 1);
+  const int start_ptex_face_index = data->reshape_ctx.face_ptex_offset[coarse_poly_index];
+  const bool is_quad = (coarse_poly->totloop == 4);
+  for (int corner = 0; corner < coarse_poly->totloop; corner++) {
+    for (int y = 0; y < resolution; y++) {
+      const float corner_v = y * resolution_1_inv;
+      for (int x = 0; x < resolution; x++) {
+        const float corner_u = x * resolution_1_inv;
+        /* Quad faces consists of a single ptex face. */
+        const int ptex_face_index = is_quad ? start_ptex_face_index :
+                                              start_ptex_face_index + corner;
+        float grid_u, grid_v;
+        BKE_subdiv_ptex_face_uv_to_grid_uv(corner_u, corner_v, &grid_u, &grid_v);
+        /*const*/ CCGElem *grid = grids[coarse_poly->loopstart + corner];
+        /*const*/ CCGElem *grid_element = CCG_grid_elem(
+            key, grid, key_grid_size_1 * grid_u, key_grid_size_1 * grid_v);
+        const float *final_P = CCG_elem_co(key, grid_element);
+        float final_mask = 0.0f;
+        if (key->has_mask) {
+          final_mask = *CCG_elem_mask(key, grid_element);
+        }
+        multires_reshape_vertex_from_final_data(&data->reshape_ctx,
+                                                ptex_face_index,
+                                                corner_u,
+                                                corner_v,
+                                                coarse_poly_index,
+                                                corner,
+                                                final_P,
+                                                final_mask);
+      }
+    }
+  }
+}
+
+bool multiresModifier_reshapeFromCCG(const int tot_level, Mesh *coarse_mesh, SubdivCCG *subdiv_ccg)
+{
+  CCGKey key;
+  BKE_subdiv_ccg_key_top_level(&key, subdiv_ccg);
+  /* Sanity checks. */
+  if (coarse_mesh->totloop != subdiv_ccg->num_grids) {
+    /* Grids are supposed to eb created for each face-cornder (aka loop). */
+    return false;
+  }
+  MDisps *mdisps = CustomData_get_layer(&coarse_mesh->ldata, CD_MDISPS);
+  if (mdisps == NULL) {
+    /* Multires displacement has been removed before current changes were
+     * applies to all the levels. */
+    return false;
+  }
+  GridPaintMask *grid_paint_mask = CustomData_get_layer(&coarse_mesh->ldata, CD_GRID_PAINT_MASK);
+  Subdiv *subdiv = subdiv_ccg->subdiv;
+  /* Pick maximum between multires level and displacement level.
+   * This is because mesh can be used by objects with multires at different
+   * levels.
+   *
+   * TODO(sergey): At this point it should be possible to always use
+   * mdisps->level. */
+  const int top_level = max_ii(tot_level, mdisps->level);
+  /* Make sure displacement grids are ready. */
+  multires_reshape_ensure_grids(coarse_mesh, top_level);
+  /* Construct context. */
+  ReshapeFromCCGTaskData data = {
+      .reshape_ctx =
+          {
+              .subdiv = subdiv,
+              .coarse_mesh = coarse_mesh,
+              .mdisps = mdisps,
+              .grid_paint_mask = grid_paint_mask,
+              .top_grid_size = BKE_subdiv_grid_size_from_level(top_level),
+              .top_level = top_level,
+              .face_ptex_offset = BKE_subdiv_face_ptex_offset_get(subdiv),
+          },
+      .key = &key,
+      .grids = subdiv_ccg->grids,
+  };
+  /* Initialize propagation to higher levels. */
+  MultiresPropagateData propagate_data;
+  multires_reshape_propagate_prepare(&propagate_data, coarse_mesh, key.level, top_level);
+  /* Threaded grids iteration. */
+  TaskParallelSettings parallel_range_settings;
+  BLI_parallel_range_settings_defaults(&parallel_range_settings);
+  BLI_task_parallel_range(
+      0, coarse_mesh->totpoly, &data, reshape_from_ccg_task, &parallel_range_settings);
+  /* Update higher levels if needed. */
+  multires_reshape_propagate(&propagate_data);
+  multires_reshape_propagate_free(&propagate_data);
+  return true;
+}