From 2fb31f34af84c39116742e20a12222099cd0ff9a Mon Sep 17 00:00:00 2001
From: Jacques Lucke <jacques@blender.org>
Date: Wed, 2 Mar 2022 17:12:56 +0100
Subject: Fix T95692: incorrect interpolated children particle hair

Differential Revision: https://developer.blender.org/D14227
---
 source/blender/blenkernel/BKE_particle.h           |  3 +-
 source/blender/blenkernel/intern/particle.c        | 33 ++++++++++++++++++----
 .../blenkernel/intern/particle_distribute.c        |  5 +++-
 3 files changed, 34 insertions(+), 7 deletions(-)

(limited to 'source/blender/blenkernel')

diff --git a/source/blender/blenkernel/BKE_particle.h b/source/blender/blenkernel/BKE_particle.h
index 804331a3412..d39796ddbd1 100644
--- a/source/blender/blenkernel/BKE_particle.h
+++ b/source/blender/blenkernel/BKE_particle.h
@@ -596,7 +596,8 @@ void psys_get_texture(struct ParticleSimulationData *sim,
 /**
  * Interpolate a location on a face based on face coordinates.
  */
-void psys_interpolate_face(struct MVert *mvert,
+void psys_interpolate_face(struct Mesh *mesh,
+                           struct MVert *mvert,
                            const float (*vert_normals)[3],
                            struct MFace *mface,
                            struct MTFace *tface,
diff --git a/source/blender/blenkernel/intern/particle.c b/source/blender/blenkernel/intern/particle.c
index 4dba13ce4c2..80f0ecd6baa 100644
--- a/source/blender/blenkernel/intern/particle.c
+++ b/source/blender/blenkernel/intern/particle.c
@@ -1673,7 +1673,8 @@ static void interpolate_pathcache(ParticleCacheKey *first, float t, ParticleCach
 /*          Particles on a dm                   */
 /************************************************/
 
-void psys_interpolate_face(MVert *mvert,
+void psys_interpolate_face(Mesh *mesh,
+                           MVert *mvert,
                            const float (*vert_normals)[3],
                            MFace *mface,
                            MTFace *tface,
@@ -1793,6 +1794,7 @@ void psys_interpolate_face(MVert *mvert,
       else {
         interp_v3_v3v3v3(orco, o1, o2, o3, w);
       }
+      BKE_mesh_orco_verts_transform(mesh, (float(*)[3])orco, 1, true);
     }
     else {
       copy_v3_v3(orco, vec);
@@ -2137,6 +2139,7 @@ void psys_particle_on_dm(Mesh *mesh_final,
     if (orco) {
       if (orcodata) {
         copy_v3_v3(orco, orcodata[mapindex]);
+        BKE_mesh_orco_verts_transform(mesh_final, (float(*)[3])orco, 1, true);
       }
       else {
         copy_v3_v3(orco, vec);
@@ -2162,8 +2165,18 @@ void psys_particle_on_dm(Mesh *mesh_final,
     }
 
     if (from == PART_FROM_VOLUME) {
-      psys_interpolate_face(
-          mvert, vert_normals, mface, mtface, orcodata, mapfw, vec, tmpnor, utan, vtan, orco);
+      psys_interpolate_face(mesh_final,
+                            mvert,
+                            vert_normals,
+                            mface,
+                            mtface,
+                            orcodata,
+                            mapfw,
+                            vec,
+                            tmpnor,
+                            utan,
+                            vtan,
+                            orco);
       if (nor) {
         copy_v3_v3(nor, tmpnor);
       }
@@ -2175,8 +2188,18 @@ void psys_particle_on_dm(Mesh *mesh_final,
       add_v3_v3(vec, tmpnor);
     }
     else {
-      psys_interpolate_face(
-          mvert, vert_normals, mface, mtface, orcodata, mapfw, vec, nor, utan, vtan, orco);
+      psys_interpolate_face(mesh_final,
+                            mvert,
+                            vert_normals,
+                            mface,
+                            mtface,
+                            orcodata,
+                            mapfw,
+                            vec,
+                            nor,
+                            utan,
+                            vtan,
+                            orco);
     }
   }
 }
diff --git a/source/blender/blenkernel/intern/particle_distribute.c b/source/blender/blenkernel/intern/particle_distribute.c
index ba3f99a2800..d8da3b5a497 100644
--- a/source/blender/blenkernel/intern/particle_distribute.c
+++ b/source/blender/blenkernel/intern/particle_distribute.c
@@ -627,7 +627,7 @@ static void distribute_from_volume_exec(ParticleTask *thread, ParticleData *pa,
   tot = mesh->totface;
 
   psys_interpolate_face(
-      mvert, BKE_mesh_vertex_normals_ensure(mesh), mface, 0, 0, pa->fuv, co, nor, 0, 0, 0);
+      mesh, mvert, BKE_mesh_vertex_normals_ensure(mesh), mface, 0, 0, pa->fuv, co, nor, 0, 0, 0);
 
   normalize_v3(nor);
   negate_v3(nor);
@@ -958,6 +958,9 @@ static int psys_thread_context_init_distribute(ParticleThreadContext *ctx,
     }
   }
 
+  /* After this #BKE_mesh_orco_verts_transform can be used safely from multiple threads. */
+  BKE_mesh_texspace_ensure(final_mesh);
+
   /* Create trees and original coordinates if needed */
   if (from == PART_FROM_CHILD) {
     distr = PART_DISTR_RAND;
-- 
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