4 files changed, 36 insertions, 15 deletions

diff --git a/source/blender/editors/mesh/meshtools.cc b/source/blender/editors/mesh/meshtools.cc
index e9a34cf95cb..330560be026 100644
--- a/source/blender/editors/mesh/meshtools.cc
+++ b/source/blender/editors/mesh/meshtools.cc
@@ -10,6 +10,8 @@
 
 #include "MEM_guardedalloc.h"
 
+#include "BLI_virtual_array.hh"
+
 #include "DNA_key_types.h"
 #include "DNA_material_types.h"
 #include "DNA_mesh_types.h"
@@ -21,6 +23,7 @@
 #include "DNA_view3d_types.h"
 #include "DNA_workspace_types.h"
 
+#include "BKE_attribute.hh"
 #include "BKE_context.h"
 #include "BKE_customdata.h"
 #include "BKE_deform.h"
@@ -247,9 +250,19 @@ static void join_mesh_single(Depsgraph *depsgraph,
     CustomData_merge(&me->pdata, pdata, CD_MASK_MESH.pmask, CD_SET_DEFAULT, totpoly);
     CustomData_copy_data_named(&me->pdata, pdata, 0, *polyofs, me->totpoly);
 
+    blender::bke::AttributeWriter<int> material_indices =
+        blender::bke::mesh_attributes_for_write(*me).lookup_for_write<int>("material_index");
+    if (material_indices) {
+      blender::MutableVArraySpan<int> material_indices_span(material_indices.varray);
+      for (const int i : material_indices_span.index_range()) {
+        material_indices_span[i] = matmap ? matmap[material_indices_span[i]] : 0;
+      }
+      material_indices_span.save();
+      material_indices.finish();
+    }
+
     for (a = 0; a < me->totpoly; a++, mpoly++) {
       mpoly->loopstart += *loopofs;
-      mpoly->mat_nr = matmap ? matmap[mpoly->mat_nr] : 0;
     }
 
     /* Face maps. */
diff --git a/source/blender/editors/object/object_bake.c b/source/blender/editors/object/object_bake.c
index effbde41c38..3170ce2c620 100644
--- a/source/blender/editors/object/object_bake.c
+++ b/source/blender/editors/object/object_bake.c
@@ -161,9 +161,10 @@ static bool multiresbake_check(bContext *C, wmOperator *op)
       ok = false;
     }
     else {
+      const int *material_indices = BKE_mesh_material_indices(me);
       a = me->totpoly;
       while (ok && a--) {
-        Image *ima = bake_object_image_get(ob, me->mpoly[a].mat_nr);
+        Image *ima = bake_object_image_get(ob, material_indices ? material_indices[a] : 0);
 
         if (!ima) {
           BKE_report(
diff --git a/source/blender/editors/sculpt_paint/paint_image_proj.c b/source/blender/editors/sculpt_paint/paint_image_proj.c
index 3e5ad9bdc2d..909ae1c783a 100644
--- a/source/blender/editors/sculpt_paint/paint_image_proj.c
+++ b/source/blender/editors/sculpt_paint/paint_image_proj.c
@@ -414,6 +414,7 @@ typedef struct ProjPaintState {
   const float (*vert_normals)[3];
   const MEdge *medge_eval;
   const MPoly *mpoly_eval;
+  const int *material_indices;
   const MLoop *mloop_eval;
   const MLoopTri *mlooptri_eval;
 
@@ -542,8 +543,8 @@ static int project_paint_face_paint_tile(Image *ima, const float *uv)
 
 static TexPaintSlot *project_paint_face_paint_slot(const ProjPaintState *ps, int tri_index)
 {
-  const MPoly *mp = ps_tri_index_to_mpoly(ps, tri_index);
-  Material *ma = ps->mat_array[mp->mat_nr];
+  const int poly_i = ps->mlooptri_eval[tri_index].poly;
+  Material *ma = ps->mat_array[ps->material_indices == NULL ? 0 : ps->material_indices[poly_i]];
   return ma ? ma->texpaintslot + ma->paint_active_slot : NULL;
 }
 
@@ -553,23 +554,23 @@ static Image *project_paint_face_paint_image(const ProjPaintState *ps, int tri_i
     return ps->stencil_ima;
   }
 
-  const MPoly *mp = ps_tri_index_to_mpoly(ps, tri_index);
-  Material *ma = ps->mat_array[mp->mat_nr];
+  const int poly_i = ps->mlooptri_eval[tri_index].poly;
+  Material *ma = ps->mat_array[ps->material_indices == NULL ? 0 : ps->material_indices[poly_i]];
   TexPaintSlot *slot = ma ? ma->texpaintslot + ma->paint_active_slot : NULL;
   return slot ? slot->ima : ps->canvas_ima;
 }
 
 static TexPaintSlot *project_paint_face_clone_slot(const ProjPaintState *ps, int tri_index)
 {
-  const MPoly *mp = ps_tri_index_to_mpoly(ps, tri_index);
-  Material *ma = ps->mat_array[mp->mat_nr];
+  const int poly_i = ps->mlooptri_eval[tri_index].poly;
+  Material *ma = ps->mat_array[ps->material_indices == NULL ? 0 : ps->material_indices[poly_i]];
   return ma ? ma->texpaintslot + ma->paint_clone_slot : NULL;
 }
 
 static Image *project_paint_face_clone_image(const ProjPaintState *ps, int tri_index)
 {
-  const MPoly *mp = ps_tri_index_to_mpoly(ps, tri_index);
-  Material *ma = ps->mat_array[mp->mat_nr];
+  const int poly_i = ps->mlooptri_eval[tri_index].poly;
+  Material *ma = ps->mat_array[ps->material_indices == NULL ? 0 : ps->material_indices[poly_i]];
   TexPaintSlot *slot = ma ? ma->texpaintslot + ma->paint_clone_slot : NULL;
   return slot ? slot->ima : ps->clone_ima;
 }
@@ -4060,6 +4061,8 @@ static bool proj_paint_state_mesh_eval_init(const bContext *C, ProjPaintState *p
   }
   ps->mloop_eval = ps->me_eval->mloop;
   ps->mpoly_eval = ps->me_eval->mpoly;
+  ps->material_indices = (const int *)CustomData_get_layer_named(
+      &ps->me_eval->pdata, CD_PROP_INT32, "material_index");
 
   ps->totvert_eval = ps->me_eval->totvert;
   ps->totedge_eval = ps->me_eval->totedge;
diff --git a/source/blender/editors/sculpt_paint/paint_utils.c b/source/blender/editors/sculpt_paint/paint_utils.c
index 1f272882100..1429744aca7 100644
--- a/source/blender/editors/sculpt_paint/paint_utils.c
+++ b/source/blender/editors/sculpt_paint/paint_utils.c
@@ -287,7 +287,6 @@ static void imapaint_pick_uv(
   const int tottri = me_eval->runtime.looptris.len;
 
   const MVert *mvert = me_eval->mvert;
-  const MPoly *mpoly = me_eval->mpoly;
   const MLoop *mloop = me_eval->mloop;
   const int *index_mp_to_orig = CustomData_get_layer(&me_eval->pdata, CD_ORIGINDEX);
 
@@ -302,6 +301,9 @@ static void imapaint_pick_uv(
   minabsw = 1e10;
   uv[0] = uv[1] = 0.0;
 
+  const int *material_indices = (const int *)CustomData_get_layer_named(
+      &me_eval->pdata, CD_PROP_INT32, "material_index");
+
   /* test all faces in the derivedmesh with the original index of the picked face */
   /* face means poly here, not triangle, indeed */
   for (i = 0; i < tottri; i++, lt++) {
@@ -309,7 +311,6 @@ static void imapaint_pick_uv(
 
     if (findex == faceindex) {
       const MLoopUV *mloopuv;
-      const MPoly *mp = &mpoly[lt->poly];
       const MLoopUV *tri_uv[3];
       float tri_co[3][3];
 
@@ -321,7 +322,8 @@ static void imapaint_pick_uv(
         const Material *ma;
         const TexPaintSlot *slot;
 
-        ma = BKE_object_material_get(ob_eval, mp->mat_nr + 1);
+        ma = BKE_object_material_get(
+            ob_eval, material_indices == NULL ? 1 : material_indices[lt->poly] + 1);
         slot = &ma->texpaintslot[ma->paint_active_slot];
 
         if (!(slot && slot->uvname &&
@@ -410,6 +412,8 @@ void paint_sample_color(
       cddata_masks.pmask |= CD_MASK_ORIGINDEX;
       Mesh *me = (Mesh *)ob->data;
       Mesh *me_eval = mesh_get_eval_final(depsgraph, scene, ob_eval, &cddata_masks);
+      const int *material_indices = (const int *)CustomData_get_layer_named(
+          &me_eval->pdata, CD_PROP_INT32, "material_index");
 
       ViewContext vc;
       const int mval[2] = {x, y};
@@ -427,8 +431,8 @@ void paint_sample_color(
 
           if (use_material) {
             /* Image and texture interpolation from material. */
-            MPoly *mp = me_eval->mpoly + faceindex;
-            Material *ma = BKE_object_material_get(ob_eval, mp->mat_nr + 1);
+            Material *ma = BKE_object_material_get(
+                ob_eval, material_indices ? material_indices[faceindex] + 1 : 1);
 
             /* Force refresh since paint slots are not updated when changing interpolation. */
             BKE_texpaint_slot_refresh_cache(scene, ma, ob);