Fix T75981: crash in sculpt mode with mesh that used to have multiple materials

The material indices in a mesh can exceed the number of available materials
slots in the object or mesh, sculpt drawing was not taking that into account.

4 files changed, 19 insertions, 7 deletions

diff --git a/source/blender/draw/engines/eevee/eevee_materials.c b/source/blender/draw/engines/eevee/eevee_materials.c
index 10ad8f3f1be..dca9f2901ab 100644
--- a/source/blender/draw/engines/eevee/eevee_materials.c
+++ b/source/blender/draw/engines/eevee/eevee_materials.c
@@ -2089,16 +2089,16 @@ void EEVEE_materials_cache_populate(EEVEE_Data *vedata,
         for (int i = 0; i < materials_len; i++) {
           sculpt_shgrps_array[i] = shgrps_array[i].shading_grp;
         }
-        DRW_shgroup_call_sculpt_with_materials(sculpt_shgrps_array, ob, use_vcol);
+        DRW_shgroup_call_sculpt_with_materials(sculpt_shgrps_array, materials_len, ob, use_vcol);
 
         for (int i = 0; i < materials_len; i++) {
           sculpt_shgrps_array[i] = shgrps_array[i].depth_grp;
         }
-        DRW_shgroup_call_sculpt_with_materials(sculpt_shgrps_array, ob, use_vcol);
+        DRW_shgroup_call_sculpt_with_materials(sculpt_shgrps_array, materials_len, ob, use_vcol);
         for (int i = 0; i < materials_len; i++) {
           sculpt_shgrps_array[i] = shgrps_array[i].depth_clip_grp;
         }
-        DRW_shgroup_call_sculpt_with_materials(sculpt_shgrps_array, ob, use_vcol);
+        DRW_shgroup_call_sculpt_with_materials(sculpt_shgrps_array, materials_len, ob, use_vcol);
 
         for (int renderpass_index = 0;
              renderpass_index < stl->g_data->render_passes_material_count;
@@ -2106,7 +2106,7 @@ void EEVEE_materials_cache_populate(EEVEE_Data *vedata,
           for (int i = 0; i < materials_len; i++) {
             sculpt_shgrps_array[i] = shgrps_array[i].material_accum_grp[renderpass_index];
           }
-          DRW_shgroup_call_sculpt_with_materials(sculpt_shgrps_array, ob, use_vcol);
+          DRW_shgroup_call_sculpt_with_materials(sculpt_shgrps_array, materials_len, ob, use_vcol);
         }
 
         /* TODO(fclem): Support shadows in sculpt mode. */
diff --git a/source/blender/draw/engines/workbench/workbench_engine.c b/source/blender/draw/engines/workbench/workbench_engine.c
index c6c594dc04d..f3554f32205 100644
--- a/source/blender/draw/engines/workbench/workbench_engine.c
+++ b/source/blender/draw/engines/workbench/workbench_engine.c
@@ -126,7 +126,7 @@ static void workbench_cache_sculpt_populate(WORKBENCH_PrivateData *wpd,
     for (int i = 0; i < materials_len; i++) {
       shgrps[i] = workbench_material_setup(wpd, ob, i + 1, color_type, NULL);
     }
-    DRW_shgroup_call_sculpt_with_materials(shgrps, ob, false);
+    DRW_shgroup_call_sculpt_with_materials(shgrps, materials_len, ob, false);
   }
 }
 
diff --git a/source/blender/draw/intern/DRW_render.h b/source/blender/draw/intern/DRW_render.h
index de4bf0303fe..663567fd51e 100644
--- a/source/blender/draw/intern/DRW_render.h
+++ b/source/blender/draw/intern/DRW_render.h
@@ -411,7 +411,10 @@ void DRW_shgroup_call_instances_with_attrs(DRWShadingGroup *shgroup,
                                            struct GPUBatch *inst_attributes);
 
 void DRW_shgroup_call_sculpt(DRWShadingGroup *sh, Object *ob, bool wire, bool mask, bool vcol);
-void DRW_shgroup_call_sculpt_with_materials(DRWShadingGroup **sh, Object *ob, bool vcol);
+void DRW_shgroup_call_sculpt_with_materials(DRWShadingGroup **sh,
+                                            int num_sh,
+                                            Object *ob,
+                                            bool vcol);
 
 DRWCallBuffer *DRW_shgroup_call_buffer(DRWShadingGroup *shading_group,
                                        struct GPUVertFormat *format,
diff --git a/source/blender/draw/intern/draw_manager_data.c b/source/blender/draw/intern/draw_manager_data.c
index 0544bb3c49b..1d0fe957631 100644
--- a/source/blender/draw/intern/draw_manager_data.c
+++ b/source/blender/draw/intern/draw_manager_data.c
@@ -858,6 +858,7 @@ void DRW_shgroup_call_instances_with_attrs(DRWShadingGroup *shgroup,
 typedef struct DRWSculptCallbackData {
   Object *ob;
   DRWShadingGroup **shading_groups;
+  int num_shading_groups;
   bool use_wire;
   bool use_mats;
   bool use_mask;
@@ -896,6 +897,9 @@ static void sculpt_draw_cb(DRWSculptCallbackData *scd, GPU_PBVH_Buffers *buffers
 
   if (scd->use_mats) {
     index = GPU_pbvh_buffers_material_index_get(buffers);
+    if (index >= scd->num_shading_groups) {
+      index = 0;
+    }
   }
 
   DRWShadingGroup *shgrp = scd->shading_groups[index];
@@ -1035,6 +1039,7 @@ void DRW_shgroup_call_sculpt(
   DRWSculptCallbackData scd = {
       .ob = ob,
       .shading_groups = &shgroup,
+      .num_shading_groups = 1,
       .use_wire = use_wire,
       .use_mats = false,
       .use_mask = use_mask,
@@ -1042,11 +1047,15 @@ void DRW_shgroup_call_sculpt(
   drw_sculpt_generate_calls(&scd, use_vcol);
 }
 
-void DRW_shgroup_call_sculpt_with_materials(DRWShadingGroup **shgroups, Object *ob, bool use_vcol)
+void DRW_shgroup_call_sculpt_with_materials(DRWShadingGroup **shgroups,
+                                            int num_shgroups,
+                                            Object *ob,
+                                            bool use_vcol)
 {
   DRWSculptCallbackData scd = {
       .ob = ob,
       .shading_groups = shgroups,
+      .num_shading_groups = num_shgroups,
       .use_wire = false,
       .use_mats = true,
       .use_mask = false,