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Fix T46455: Array modifier could generate chained mapping of vertices, leading to corrupted geometry. 

That was the main issue (in both T46455 and T46690), solved by 'flattening' those chains (v1 -> v2 ->v3 etc.)
before calling `CDDM_merge_verts()`.

Also added note to `CDDM_merge_verts()` that it does not support chained mapping, along with
a basic assert that should catch most of those cases in future.

The logic of 'following mapping' was also rather broken, making a special case here when using
object-controlled offset is very weak. Further more, blindly following mapping in this case
was far from ideal, this could end to merging vertices rather far from each other.

To address this issue, we now always follow mapping, but only as long as 'final' vertex remains
close enough from mapped one.

Finally, the search of 'closest' vertex to merge with was also quite bad, would just pick the first
one matching distance limit, instead of using the actual closest one - could lead to rather ugly
geometry deformations in case one would use not-so-small merge threashold!
This commit is contained in:
Bastien Montagne 2016-01-30 17:17:05 +01:00
parent bde80cbb14
commit eed9c6fdcf
Notes: blender-bot 2023-03-24 17:05:22 +01:00 
Referenced by issue #46455, Applying Array Modifier corrupt mesh
2 changed files with 47 additions and 37 deletions
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7
source/blender/blenkernel/intern/cdderivedmesh.c
View File

@ -2913,6 +2913,8 @@ static bool poly_gset_compare_fn(const void *k1, const void *k2)
* \param vtargetmap The table that maps vertices to target vertices. a value of -1
* indicates a vertex is a target, and is to be kept.
* This array is aligned with 'dm->numVertData'
* \warning \a vtergatmap must **not** contain any chained mapping (v1 -> v2 -> v3 etc.), this is not supported
* and will likely generate corrupted geometry.
*
* \param tot_vtargetmap The number of non '-1' values in vtargetmap. (not the size)
*
@ -3221,7 +3223,10 @@ DerivedMesh *CDDM_merge_verts(DerivedMesh *dm, const int *vtargetmap, const int
med->v1 = newv[med->v1];
if (newv[med->v2] != -1)
med->v2 = newv[med->v2];
/* Can happen in case vtargetmap contains some double chains, we do not support that. */
BLI_assert(med->v1 != med->v2);
CustomData_copy_data(&dm->edgeData, &cddm2->dm.edgeData, olde[i], i, 1);
}

77
source/blender/modifiers/intern/MOD_array.c
View File

@ -222,8 +222,7 @@ static void dm_mvert_map_doubles(
const int target_num_verts,
const int source_start,
const int source_num_verts,
const float dist,
const bool with_follow)
const float dist)
{
const float dist3 = ((float)M_SQRT3 + 0.00005f) * dist; /* Just above sqrt(3) */
int i_source, i_target, i_target_low_bound, target_end, source_end;
@ -258,7 +257,8 @@ static void dm_mvert_map_doubles(
i_source < source_num_verts;
i_source++, sve_source++)
{
bool double_found;
int best_target_vertex = -1;
float best_dist_sq = dist * dist;
float sve_source_sumco;
/* If source has already been assigned to a target (in an earlier call, with other chunks) */
@ -294,37 +294,38 @@ static void dm_mvert_map_doubles(
/* i_target will scan vertices in the [v_source_sumco - dist3; v_source_sumco + dist3] range */
double_found = false;
while ((i_target < target_num_verts) &&
(sve_target->sum_co <= sve_source_sumco + dist3))
{
/* Testing distance for candidate double in target */
/* v_target is within dist3 of v_source in terms of sumco; check real distance */
if (compare_len_v3v3(sve_source->co, sve_target->co, dist)) {
/* Double found */
/* If double target is itself already mapped to other vertex,
* behavior depends on with_follow option */
int target_vertex = sve_target->vertex_num;
if (doubles_map[target_vertex] != -1) {
if (with_follow) { /* with_follow option: map to initial target */
target_vertex = doubles_map[target_vertex];
float dist_sq;
if ((dist_sq = len_squared_v3v3(sve_source->co, sve_target->co)) <= best_dist_sq) {
/* Potential double found */
best_dist_sq = dist_sq;
best_target_vertex = sve_target->vertex_num;
/* If target is already mapped, we only follow that mapping if final target remains
* close enough from current vert (otherwise no mapping at all).
* Note that if we later find another target closer than this one, then we check it. But if other
* potential targets are farther, then there will be no mapping at all for this source. */
while (best_target_vertex != -1 && !ELEM(doubles_map[best_target_vertex], -1, best_target_vertex)) {
if (compare_len_v3v3(mverts[sve_source->vertex_num].co,
mverts[doubles_map[best_target_vertex]].co,
dist))
{
best_target_vertex = doubles_map[best_target_vertex];
}
else {
/* not with_follow: if target is mapped, then we do not map source, and stop searching */
break;
best_target_vertex = -1;
}
}
doubles_map[sve_source->vertex_num] = target_vertex;
double_found = true;
break;
}
i_target++;
sve_target++;
}
/* End of candidate scan: if none found then no doubles */
if (!double_found) {
doubles_map[sve_source->vertex_num] = -1;
}
doubles_map[sve_source->vertex_num] = best_target_vertex;
}
MEM_freeN(sorted_verts_source);
@ -431,8 +432,6 @@ static DerivedMesh *arrayModifier_doArray(
const bool use_merge = (amd->flags & MOD_ARR_MERGE) != 0;
const bool use_recalc_normals = (dm->dirty & DM_DIRTY_NORMALS) || use_merge;
const bool use_offset_ob = ((amd->offset_type & MOD_ARR_OFF_OBJ) && amd->offset_ob);
/* allow pole vertices to be used by many faces */
const bool with_follow = use_offset_ob;
int start_cap_nverts = 0, start_cap_nedges = 0, start_cap_npolys = 0, start_cap_nloops = 0;
int end_cap_nverts = 0, end_cap_nedges = 0, end_cap_npolys = 0, end_cap_nloops = 0;
@ -633,13 +632,16 @@ static DerivedMesh *arrayModifier_doArray(
int target = full_doubles_map[prev_chunk_index];
if (target != -1) {
target += chunk_nverts; /* translate mapping */
if (full_doubles_map[target] != -1) {
if (with_follow) {
while (target != -1 && !ELEM(full_doubles_map[target], -1, target)) {
/* If target is already mapped, we only follow that mapping if final target remains
* close enough from current vert (otherwise no mapping at all). */
if (compare_len_v3v3(result_dm_verts[this_chunk_index].co,
result_dm_verts[full_doubles_map[target]].co,
amd->merge_dist))
{
target = full_doubles_map[target];
}
else {
/* The rule here is to not follow mapping to chunk N-2, which could be too far
* so if target vertex was itself mapped, then this vertex is not mapped */
target = -1;
}
}
@ -655,8 +657,7 @@ static DerivedMesh *arrayModifier_doArray(
chunk_nverts,
c * chunk_nverts,
chunk_nverts,
amd->merge_dist,
with_follow);
amd->merge_dist);
}
}
}
@ -675,8 +676,7 @@ static DerivedMesh *arrayModifier_doArray(
last_chunk_nverts,
first_chunk_start,
first_chunk_nverts,
amd->merge_dist,
with_follow);
amd->merge_dist);
}
/* start capping */
@ -700,8 +700,7 @@ static DerivedMesh *arrayModifier_doArray(
first_chunk_nverts,
start_cap_start,
start_cap_nverts,
amd->merge_dist,
false);
amd->merge_dist);
}
}
@ -725,8 +724,7 @@ static DerivedMesh *arrayModifier_doArray(
last_chunk_nverts,
end_cap_start,
end_cap_nverts,
amd->merge_dist,
false);
amd->merge_dist);
}
}
/* done capping */
@ -735,11 +733,18 @@ static DerivedMesh *arrayModifier_doArray(
tot_doubles = 0;
if (use_merge) {
for (i = 0; i < result_nverts; i++) {
if (full_doubles_map[i] != -1) {
if (i == full_doubles_map[i]) {
int new_i = full_doubles_map[i];
if (new_i != -1) {
/* We have to follow chains of doubles (merge start/end especially is likely to create some),
* those are not supported at all by CDDM_merge_verts! */
while (!ELEM(full_doubles_map[new_i], -1, new_i)) {
new_i = full_doubles_map[new_i];
}
if (i == new_i) {
full_doubles_map[i] = -1;
}
else {
full_doubles_map[i] = new_i;
tot_doubles++;
}
}