source/blender/draw/engines/workbench/workbench_engine.cc

@@ -207,8 +207,6 @@ class Instance {
             if (batches[i] == nullptr) {
               continue;
             }
-            ResourceHandle _handle = handle;
-            _handle.sub_index = i;
 
             Material &mat = resources.material_buf.get_or_resize(material_count++);
 
@@ -228,7 +226,10 @@ class Instance {
               get_material_image(ob_ref.object, i + 1, image, iuser, sampler_state);
             }
 
-            draw_mesh(ob_ref, mat, batches[i], _handle, image, sampler_state, iuser);
+            if (i != 0) {
+              handle = manager.resource_sub_handle(handle);
+            }
+            draw_mesh(ob_ref, mat, batches[i], handle, image, sampler_state, iuser);
           }
         }
       }

source/blender/draw/intern/draw_manager.cc

@@ -55,6 +55,7 @@ void Manager::begin_sync()
 #endif
   resource_len_ = 0;
   attribute_len_ = 0;
+  sub_handle_indices_.clear();
   /* TODO(fclem): Resize buffers if too big, but with an hysteresis threshold. */
 
   object_active = DST.draw_ctx.obact;

source/blender/draw/intern/draw_manager.hh

@@ -109,6 +109,9 @@ class Manager {
   /** Number of object attribute recorded. */
   uint attribute_len_ = 0;
 
+  Vector<uint8_t> sub_handle_indices_;
+  int max_sub_handles_ = 64;
+
   Object *object_active = nullptr;
 
  public:
@@ -134,6 +137,12 @@ class Manager {
                                  const float3 &bounds_center,
                                  const float3 &bounds_half_extent);
 
+  /**
+   * Returns a copy of the resource handle with a unique sub-index.
+   * Or a new full copy handle when running out of sub-indices.
+   */
+  ResourceHandle resource_sub_handle(const ResourceHandle handle);
+
   /**
    * Populate additional per resource data on demand.
    */
@@ -196,6 +205,7 @@ inline ResourceHandle Manager::resource_handle(const ObjectRef ref)
   matrix_buf.current().get_or_resize(resource_len_).sync(*ref.object);
   bounds_buf.current().get_or_resize(resource_len_).sync(*ref.object);
   infos_buf.current().get_or_resize(resource_len_).sync(ref, is_active_object);
+  sub_handle_indices_.append(0);
   return ResourceHandle(resource_len_++, (ref.object->transflag & OB_NEG_SCALE) != 0);
 }
 
@@ -204,6 +214,7 @@ inline ResourceHandle Manager::resource_handle(const float4x4 &model_matrix)
   matrix_buf.current().get_or_resize(resource_len_).sync(model_matrix);
   bounds_buf.current().get_or_resize(resource_len_).sync();
   infos_buf.current().get_or_resize(resource_len_).sync();
+  sub_handle_indices_.append(0);
   return ResourceHandle(resource_len_++, false);
 }
 
@@ -214,9 +225,34 @@ inline ResourceHandle Manager::resource_handle(const float4x4 &model_matrix,
   matrix_buf.current().get_or_resize(resource_len_).sync(model_matrix);
   bounds_buf.current().get_or_resize(resource_len_).sync(bounds_center, bounds_half_extent);
   infos_buf.current().get_or_resize(resource_len_).sync();
+  sub_handle_indices_.append(0);
   return ResourceHandle(resource_len_++, false);
 }
 
+inline ResourceHandle Manager::resource_sub_handle(const ResourceHandle handle)
+{
+  const uint i = handle.resource_index();
+
+  /* Always call resource_sub_handle_with a new handle or its last created sub-handle.
+   * This avoids reaching a point where a handle has been already saturated and each call to this
+   * function creates a new copy.*/
+  BLI_assert(handle.sub_index == sub_handle_indices_[i]);
+
+  if (++sub_handle_indices_[i] < max_sub_handles_) {
+    ResourceHandle sub_handle = handle;
+    sub_handle.sub_index = sub_handle_indices_[i];
+    return sub_handle;
+  }
+  else {
+    /* Can't add more sub handles, make a full copy instead. */
+    matrix_buf.current().get_or_resize(resource_len_) = matrix_buf.current()[i];
+    bounds_buf.current().get_or_resize(resource_len_) = bounds_buf.current()[i];
+    infos_buf.current().get_or_resize(resource_len_) = infos_buf.current()[i];
+    sub_handle_indices_.append(0);
+    return ResourceHandle(resource_len_++, handle.has_inverted_handedness());
+  }
+}
+
 inline void Manager::extract_object_attributes(ResourceHandle handle,
                                                const ObjectRef &ref,
                                                Span<GPUMaterial *> materials)