source/blender/draw/engines/overlay/overlay_background.hh

@@ -19,12 +19,14 @@
 
 namespace blender::draw::overlay {
 
-class Background {
+template<typename SelectEngineT> class Background {
+  using ResourcesT = Resources<SelectEngineT>;
+
  private:
   PassSimple bg_ps_ = {"Background"};
 
  public:
-  void begin_sync(Resources &res, const State &state)
+  void begin_sync(ResourcesT &res, const State &state)
   {
     DRWState pass_state = DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND_BACKGROUND;
     float4 color_override(0.0f, 0.0f, 0.0f, 0.0f);
@@ -92,7 +94,7 @@ class Background {
     }
   }
 
-  void draw(Resources &res, Manager &manager)
+  void draw(ResourcesT &res, Manager &manager)
   {
     GPU_framebuffer_bind(res.overlay_color_only_fb);
     manager.submit(bg_ps_);

source/blender/draw/engines/overlay/overlay_empty.hh

@@ -15,14 +15,15 @@
 
 namespace blender::draw::overlay {
 
-class Empties {
+template<typename SelectEngineT> class Empties {
+  using SelectID = typename SelectEngineT::ID;
+  using ResourcesT = Resources<SelectEngineT>;
+  using EmptyInstanceBuf = ShapeInstanceBuf<SelectEngineT, ExtraInstanceData>;
 
  private:
   PassSimple empty_ps_ = {"Empties"};
   PassSimple empty_in_front_ps_ = {"Empties_In_front"};
 
-  using EmptyInstanceBuf = StorageVectorBuffer<ExtraInstanceData>;
-
   struct CallBuffers {
     EmptyInstanceBuf plain_axes_buf = {"plain_axes_buf"};
     EmptyInstanceBuf single_arrow_buf = {"single_arrow_buf"};
@@ -49,7 +50,7 @@ class Empties {
     }
   }
 
-  void object_sync(const ObjectRef &ob_ref, const Resources &res, const State &state)
+  void object_sync(const ObjectRef &ob_ref, ResourcesT &res, const State &state)
   {
     CallBuffers &call_bufs = call_buffers_[int((ob_ref.object->dtx & OB_DRAW_IN_FRONT) != 0)];
 
@@ -57,36 +58,39 @@ class Empties {
     ExtraInstanceData data(
         float4x4(ob_ref.object->object_to_world), color, ob_ref.object->empty_drawsize);
 
+    /* TODO(fclem): Get selection ID from the selection engine. */
+    const SelectID select_id = res.select_id(ob_ref);
+
     switch (ob_ref.object->empty_drawtype) {
       case OB_PLAINAXES:
-        call_bufs.plain_axes_buf.append(data);
+        call_bufs.plain_axes_buf.append(data, select_id);
         break;
       case OB_SINGLE_ARROW:
-        call_bufs.single_arrow_buf.append(data);
+        call_bufs.single_arrow_buf.append(data, select_id);
         break;
       case OB_CUBE:
-        call_bufs.cube_buf.append(data);
+        call_bufs.cube_buf.append(data, select_id);
         break;
       case OB_CIRCLE:
-        call_bufs.circle_buf.append(data);
+        call_bufs.circle_buf.append(data, select_id);
         break;
       case OB_EMPTY_SPHERE:
-        call_bufs.sphere_buf.append(data);
+        call_bufs.sphere_buf.append(data, select_id);
         break;
       case OB_EMPTY_CONE:
-        call_bufs.cone_buf.append(data);
+        call_bufs.cone_buf.append(data, select_id);
         break;
       case OB_ARROWS:
-        call_bufs.arrows_buf.append(data);
+        call_bufs.arrows_buf.append(data, select_id);
         break;
       case OB_EMPTY_IMAGE:
         /* This only show the frame. See OVERLAY_image_empty_cache_populate() for the image. */
-        call_bufs.image_buf.append(data);
+        call_bufs.image_buf.append(data, select_id);
         break;
     }
   }
 
-  void end_sync(Resources &res, ShapeCache &shapes, const State &state)
+  void end_sync(ResourcesT &res, ShapeCache &shapes, const State &state)
   {
     auto init_pass = [&](PassSimple &pass, CallBuffers &call_bufs) {
       pass.init();
@@ -95,49 +99,26 @@ class Empties {
       pass.shader_set(OVERLAY_shader_extra(false));
       pass.bind_ubo("globalsBlock", &res.globals_buf);
 
-      call_bufs.plain_axes_buf.push_update();
-      pass.bind_ssbo("data_buf", &call_bufs.plain_axes_buf);
-      pass.draw(shapes.plain_axes, call_bufs.plain_axes_buf.size());
-
-      call_bufs.single_arrow_buf.push_update();
-      pass.bind_ssbo("data_buf", &call_bufs.single_arrow_buf);
-      pass.draw(shapes.single_arrow, call_bufs.single_arrow_buf.size());
-
-      call_bufs.cube_buf.push_update();
-      pass.bind_ssbo("data_buf", &call_bufs.cube_buf);
-      pass.draw(shapes.cube, call_bufs.cube_buf.size());
-
-      call_bufs.circle_buf.push_update();
-      pass.bind_ssbo("data_buf", &call_bufs.circle_buf);
-      pass.draw(shapes.circle, call_bufs.circle_buf.size());
-
-      call_bufs.sphere_buf.push_update();
-      pass.bind_ssbo("data_buf", &call_bufs.sphere_buf);
-      pass.draw(shapes.empty_sphere, call_bufs.sphere_buf.size());
-
-      call_bufs.cone_buf.push_update();
-      pass.bind_ssbo("data_buf", &call_bufs.cone_buf);
-      pass.draw(shapes.empty_cone, call_bufs.cone_buf.size());
-
-      call_bufs.arrows_buf.push_update();
-      pass.bind_ssbo("data_buf", &call_bufs.arrows_buf);
-      pass.draw(shapes.arrows, call_bufs.arrows_buf.size());
-
-      call_bufs.image_buf.push_update();
-      pass.bind_ssbo("data_buf", &call_bufs.image_buf);
-      pass.draw(shapes.quad_wire, call_bufs.image_buf.size());
+      call_bufs.plain_axes_buf.end_sync(pass, shapes.plain_axes);
+      call_bufs.single_arrow_buf.end_sync(pass, shapes.single_arrow);
+      call_bufs.cube_buf.end_sync(pass, shapes.cube);
+      call_bufs.circle_buf.end_sync(pass, shapes.circle);
+      call_bufs.sphere_buf.end_sync(pass, shapes.empty_sphere);
+      call_bufs.cone_buf.end_sync(pass, shapes.empty_cone);
+      call_bufs.arrows_buf.end_sync(pass, shapes.arrows);
+      call_bufs.image_buf.end_sync(pass, shapes.quad_wire);
     };
     init_pass(empty_ps_, call_buffers_[0]);
     init_pass(empty_in_front_ps_, call_buffers_[1]);
   }
 
-  void draw(Resources &res, Manager &manager, View &view)
+  void draw(ResourcesT &res, Manager &manager, View &view)
   {
     GPU_framebuffer_bind(res.overlay_line_fb);
     manager.submit(empty_ps_, view);
   }
 
-  void draw_in_front(Resources &res, Manager &manager, View &view)
+  void draw_in_front(ResourcesT &res, Manager &manager, View &view)
   {
     GPU_framebuffer_bind(res.overlay_line_in_front_fb);
     manager.submit(empty_in_front_ps_, view);

source/blender/draw/engines/overlay/overlay_engine.cc

@@ -30,6 +30,10 @@
 #include "overlay_engine.h"
 #include "overlay_private.hh"
 
+using namespace blender::draw;
+
+using Instance = blender::draw::overlay::Instance<>;
+
 /* -------------------------------------------------------------------- */
 /** \name Engine Callbacks
  * \{ */
@@ -51,7 +55,7 @@ static void OVERLAY_engine_init(void *vedata)
 
   /* Allocate instance. */
   if (data->instance == nullptr) {
-    data->instance = new blender::draw::overlay::Instance();
+    data->instance = new Instance();
   }
 
   OVERLAY_PrivateData *pd = stl->pd;
@@ -737,7 +741,7 @@ static void OVERLAY_engine_free()
 
 static void OVERLAY_instance_free(void *instance_)
 {
-  blender::draw::overlay::Instance *instance = (blender::draw::overlay::Instance *)instance_;
+  auto *instance = (Instance *)instance_;
   if (instance != nullptr) {
     delete instance;
   }
@@ -748,8 +752,6 @@ static void OVERLAY_instance_free(void *instance_)
 /** \name Engine Instance
  * \{ */
 
-using namespace blender::draw;
-
 static void OVERLAY_next_engine_init(void *vedata)
 {
   if (!GPU_shader_storage_buffer_objects_support()) {
@@ -759,10 +761,10 @@ static void OVERLAY_next_engine_init(void *vedata)
   OVERLAY_Data *ved = reinterpret_cast<OVERLAY_Data *>(vedata);
 
   if (ved->instance == nullptr) {
-    ved->instance = new overlay::Instance();
+    ved->instance = new Instance();
   }
 
-  ved->instance->init();
+  reinterpret_cast<Instance *>(ved->instance)->init();
 }
 
 static void OVERLAY_next_cache_init(void *vedata)
@@ -770,7 +772,7 @@ static void OVERLAY_next_cache_init(void *vedata)
   if (!GPU_shader_storage_buffer_objects_support()) {
     return;
   }
-  reinterpret_cast<OVERLAY_Data *>(vedata)->instance->begin_sync();
+  reinterpret_cast<Instance *>(reinterpret_cast<OVERLAY_Data *>(vedata)->instance)->begin_sync();
 }
 
 static void OVERLAY_next_cache_populate(void *vedata, Object *object)
@@ -783,7 +785,8 @@ static void OVERLAY_next_cache_populate(void *vedata, Object *object)
   ref.dupli_object = DRW_object_get_dupli(object);
   ref.dupli_parent = DRW_object_get_dupli_parent(object);
 
-  reinterpret_cast<OVERLAY_Data *>(vedata)->instance->object_sync(ref);
+  reinterpret_cast<Instance *>(reinterpret_cast<OVERLAY_Data *>(vedata)->instance)
+      ->object_sync(ref);
 }
 
 static void OVERLAY_next_cache_finish(void *vedata)
@@ -791,7 +794,7 @@ static void OVERLAY_next_cache_finish(void *vedata)
   if (!GPU_shader_storage_buffer_objects_support()) {
     return;
   }
-  reinterpret_cast<OVERLAY_Data *>(vedata)->instance->end_sync();
+  reinterpret_cast<Instance *>(reinterpret_cast<OVERLAY_Data *>(vedata)->instance)->end_sync();
 }
 
 static void OVERLAY_next_draw_scene(void *vedata)
@@ -800,7 +803,8 @@ static void OVERLAY_next_draw_scene(void *vedata)
     return;
   }
 
-  reinterpret_cast<OVERLAY_Data *>(vedata)->instance->draw(*DRW_manager_get());
+  reinterpret_cast<Instance *>(reinterpret_cast<OVERLAY_Data *>(vedata)->instance)
+      ->draw(*DRW_manager_get());
 }
 
 /** \} */

source/blender/draw/engines/overlay/overlay_grid.cc

@@ -20,6 +20,10 @@
 #include "overlay_instance.hh"
 #include "overlay_private.hh"
 
+using namespace blender::draw;
+
+using Instance = blender::draw::overlay::Instance<>;
+
 BLI_STATIC_ASSERT(SI_GRID_STEPS_LEN == OVERLAY_GRID_STEPS_LEN, "")
 
 void OVERLAY_grid_init(OVERLAY_Data *vedata)
@@ -226,10 +230,11 @@ void OVERLAY_grid_cache_init(OVERLAY_Data *ved)
     return;
   }
 
-  if (ved->instance->grid_ubo == nullptr) {
-    ved->instance->grid_ubo = GPU_uniformbuf_create(sizeof(OVERLAY_GridData));
+  GPUUniformBuf *&grid_ubo = reinterpret_cast<Instance *>(ved->instance)->grid_ubo;
+  if (grid_ubo == nullptr) {
+    grid_ubo = GPU_uniformbuf_create(sizeof(OVERLAY_GridData));
   }
-  GPU_uniformbuf_update(ved->instance->grid_ubo, &pd->grid_data);
+  GPU_uniformbuf_update(grid_ubo, &pd->grid_data);
 
   DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND_ALPHA;
   DRW_PASS_CREATE(psl->grid_ps, state);
@@ -259,7 +264,7 @@ void OVERLAY_grid_cache_init(OVERLAY_Data *ved)
 
     /* Create 3 quads to render ordered transparency Z axis */
     grp = DRW_shgroup_create(sh, psl->grid_ps);
-    DRW_shgroup_uniform_block(grp, "grid_buf", ved->instance->grid_ubo);
+    DRW_shgroup_uniform_block(grp, "grid_buf", grid_ubo);
     DRW_shgroup_uniform_block(grp, "globalsBlock", G_draw.block_ubo);
     DRW_shgroup_uniform_texture_ref(grp, "depth_tx", &dtxl->depth);
 

source/blender/draw/engines/overlay/overlay_grid.hh

@@ -18,7 +18,9 @@
 
 namespace blender::draw::overlay {
 
-class Grid {
+template<typename SelectEngineT> class Grid {
+  using ResourcesT = Resources<SelectEngineT>;
+
  private:
   UniformBuffer<OVERLAY_GridData> data_;
 
@@ -164,7 +166,7 @@ class Grid {
     data_.push_update();
   }
 
-  void begin_sync(Resources &res, const State &state, const View &view)
+  void begin_sync(ResourcesT &res, const State &state, const View &view)
   {
     this->update_ubo(state, view);
 
@@ -195,7 +197,7 @@ class Grid {
     }
   }
 
-  void draw(Resources &res, Manager &manager, View &view)
+  void draw(ResourcesT &res, Manager &manager, View &view)
   {
     if (!enabled_) {
       return;

source/blender/draw/engines/overlay/overlay_instance.cc

@@ -10,7 +10,7 @@
 
 namespace blender::draw::overlay {
 
-void Instance::init()
+template<typename T> void Instance<T>::init()
 {
   resources.depth_tx.wrap(DRW_viewport_texture_list_get()->depth);
   resources.depth_in_front_tx.wrap(DRW_viewport_texture_list_get()->depth_in_front);
@@ -65,7 +65,7 @@ void Instance::init()
   resources.theme_settings = G_draw.block;
 }
 
-void Instance::begin_sync()
+template<typename T> void Instance<T>::begin_sync()
 {
   const DRWView *view_legacy = DRW_view_default_get();
   View view("OverlayView", view_legacy);
@@ -76,7 +76,7 @@ void Instance::begin_sync()
   grid.begin_sync(resources, state, view);
 }
 
-void Instance::object_sync(ObjectRef &ob_ref)
+template<typename T> void Instance<T>::object_sync(ObjectRef &ob_ref)
 {
   const bool in_edit_mode = object_is_edit_mode(ob_ref.object);
 
@@ -120,13 +120,13 @@ void Instance::object_sync(ObjectRef &ob_ref)
   }
 }
 
-void Instance::end_sync()
+template<typename T> void Instance<T>::end_sync()
 {
   metaballs.end_sync(resources, state);
   empties.end_sync(resources, shapes, state);
 }
 
-void Instance::draw(Manager &manager)
+template<typename T> void Instance<T>::draw(Manager &manager)
 {
   /* WORKAROUND: This is to prevent crashes when using depth picking or selection.
    * The selection engine should handle theses cases instead. */
@@ -182,4 +182,11 @@ void Instance::draw(Manager &manager)
   resources.depth_in_front_alloc_tx.release();
 }
 
+/* Instantiation. */
+template void Instance<>::init();
+template void Instance<>::begin_sync();
+template void Instance<>::object_sync(ObjectRef &ob_ref);
+template void Instance<>::end_sync();
+template void Instance<>::draw(Manager &manager);
+
 }  // namespace blender::draw::overlay

source/blender/draw/engines/overlay/overlay_instance.hh

@@ -14,6 +14,9 @@
 #include "overlay_metaball.hh"
 #include "overlay_shape.hh"
 
+#include "../select/select_empty.hh"
+#include "../select/select_object.hh"
+
 namespace blender::draw::overlay {
 
 class ShaderCache {
@@ -22,32 +25,12 @@ class ShaderCache {
   int clipping_enabled = 0;
 };
 
-class SceneResources {
-  ShaderCache shaders;
-
-  // UniformBuffer<ThemeColorData> theme_colors;
-  // Texture color_ramp = {"color_ramp"};
-
-  void weight_ramp_init()
-  {
-    /* Weight Painting color ramp texture */
-    // bool user_weight_ramp = (U.flag & USER_CUSTOM_RANGE) != 0;
-
-    // if (weight_ramp_custom != user_weight_ramp ||
-    //     (user_weight_ramp && memcmp(&weight_ramp_copy, &U.coba_weight, sizeof(ColorBand)) != 0))
-    //     {
-    //   DRW_TEXTURE_FREE_SAFE(G_draw.weight_ramp);
-    // }
-
-    // if (G_draw.weight_ramp == NULL) {
-    //   weight_ramp_custom = user_weight_ramp;
-    //   memcpy(&weight_ramp_copy, &U.coba_weight, sizeof(ColorBand));
-
-    //   G_draw.weight_ramp = DRW_create_weight_colorramp_texture();
-    // }
-  }
-};
-
+template<
+    /* Selection engine reuse most of the Overlay engine by creating selection IDs for each
+     * selectable component and using a special shaders for drawing.
+     * Making the select engine templated makes it easier to phase out any overhead of the
+     * selection for the regular non-selection case.*/
+    typename SelectEngineT = select::EngineEmpty>
 class Instance {
  public:
   ShaderCache shaders;
@@ -57,14 +40,14 @@ class Instance {
   GPUUniformBuf *grid_ubo = nullptr;
 
   /** Global types. */
-  Resources resources;
+  Resources<SelectEngineT> resources;
   State state;
 
   /** Overlay types. */
-  Background background;
-  Metaballs metaballs;
-  Empties empties;
-  Grid grid;
+  Background<SelectEngineT> background;
+  Metaballs<SelectEngineT> metaballs;
+  Empties<SelectEngineT> empties;
+  Grid<SelectEngineT> grid;
 
   ~Instance()
   {
@@ -109,4 +92,11 @@ class Instance {
   }
 };
 
+/* Instantiation. */
+extern template void Instance<>::init();
+extern template void Instance<>::begin_sync();
+extern template void Instance<>::object_sync(ObjectRef &ob_ref);
+extern template void Instance<>::end_sync();
+extern template void Instance<>::draw(Manager &manager);
+
 }  // namespace blender::draw::overlay

source/blender/draw/engines/overlay/overlay_metaball.hh

@@ -19,7 +19,8 @@
 
 namespace blender::draw::overlay {
 
-class Metaballs {
+template<typename SelectEngineT> class Metaballs {
+  using ResourcesT = Resources<SelectEngineT>;
 
  private:
   PassSimple metaball_ps_ = {"MetaBalls"};
@@ -50,7 +51,7 @@ class Metaballs {
     OVERLAY_bone_instance_data_set_color(data, color);
   }
 
-  void edit_object_sync(const ObjectRef &ob_ref, const Resources &res)
+  void edit_object_sync(const ObjectRef &ob_ref, const ResourcesT &res)
   {
     ArmatureSphereBuf &data_buf = (ob_ref.object->dtx & OB_DRAW_IN_FRONT) != 0 ?
                                       data_in_front_buf_ :
@@ -79,7 +80,7 @@ class Metaballs {
     }
   }
 
-  void object_sync(const ObjectRef &ob_ref, const Resources &res, const State &state)
+  void object_sync(const ObjectRef &ob_ref, const ResourcesT &res, const State &state)
   {
     ArmatureSphereBuf &data_buf = (ob_ref.object->dtx & OB_DRAW_IN_FRONT) != 0 ?
                                       data_in_front_buf_ :
@@ -96,7 +97,7 @@ class Metaballs {
     }
   }
 
-  void end_sync(Resources &res, const State &state)
+  void end_sync(ResourcesT &res, const State &state)
   {
     auto init_pass = [&](PassSimple &pass, ArmatureSphereBuf &data_buf) {
       data_buf.push_update();
@@ -113,13 +114,13 @@ class Metaballs {
     init_pass(metaball_in_front_ps_, data_in_front_buf_);
   }
 
-  void draw(Resources &res, Manager &manager, View &view)
+  void draw(ResourcesT &res, Manager &manager, View &view)
   {
     GPU_framebuffer_bind(res.overlay_line_fb);
     manager.submit(metaball_ps_, view);
   }
 
-  void draw_in_front(Resources &res, Manager &manager, View &view)
+  void draw_in_front(ResourcesT &res, Manager &manager, View &view)
   {
     GPU_framebuffer_bind(res.overlay_line_in_front_fb);
     manager.submit(metaball_in_front_ps_, view);

source/blender/draw/engines/overlay/overlay_private.hh

@@ -18,10 +18,6 @@
 
 #include "overlay_shader_shared.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifdef __APPLE__
 #  define USE_GEOM_SHADER_WORKAROUND 1
 #else
@@ -35,7 +31,7 @@ extern "C" {
 struct ImBuf;
 
 namespace blender::draw::overlay {
-class Instance;
+template<typename SelectEngineT> class Instance;
 
 struct State {
   Depsgraph *depsgraph;
@@ -68,7 +64,7 @@ using blender::draw::TextureFromPool;
 using blender::draw::TextureRef;
 using ArmatureSphereBuf = StorageVectorBuffer<float4x4>;
 
-struct Resources {
+template<typename SelectEngineT> struct Resources : public SelectEngineT::SelectMap {
   Framebuffer overlay_fb = {"overlay_fb"};
   Framebuffer overlay_in_front_fb = {"overlay_in_front_fb"};
   Framebuffer overlay_color_only_fb = {"overlay_color_only_fb"};
@@ -578,7 +574,7 @@ typedef struct OVERLAY_Data {
   OVERLAY_PassList *psl;
   OVERLAY_StorageList *stl;
 
-  blender::draw::overlay::Instance *instance;
+  void *instance;
 } OVERLAY_Data;
 
 typedef struct OVERLAY_DupliData {
@@ -927,7 +923,3 @@ GPUShader *OVERLAY_shader_xray_fade(void);
 OVERLAY_InstanceFormats *OVERLAY_shader_instance_formats_get(void);
 
 void OVERLAY_shader_free(void);
-
-#ifdef __cplusplus
-}
-#endif

source/blender/draw/engines/overlay/overlay_shader_shared.h

@@ -192,7 +192,6 @@ struct ThemeColorData {
 };
 BLI_STATIC_ASSERT_ALIGN(ThemeColorData, 16)
 
-/* TODO Move to overlay engine. */
 struct ExtraInstanceData {
   float4 color_;
   float4x4 object_to_world_;

source/blender/draw/engines/overlay/overlay_shape.hh

@@ -12,6 +12,41 @@
 
 namespace blender::draw::overlay {
 
+/**
+ * Buffer containing instances of a certain shape.
+ */
+template<typename SelectEngineT, typename InstanceDataT>
+struct ShapeInstanceBuf : private SelectEngineT::SelectBuf {
+  using SelectID = typename SelectEngineT::ID;
+
+  StorageVectorBuffer<InstanceDataT> data_buf;
+
+  ShapeInstanceBuf(const char *name = nullptr) : data_buf(name){};
+
+  void clear()
+  {
+    this->select_clear();
+    data_buf.clear();
+  }
+
+  void append(const InstanceDataT &data, SelectID select_id)
+  {
+    this->select_append(select_id);
+    data_buf.append(data);
+  }
+
+  void end_sync(PassSimple &pass, GPUBatch *shape)
+  {
+    if (data_buf.size() == 0) {
+      return;
+    }
+    this->select_bind(pass);
+    data_buf.push_update();
+    pass.bind_ssbo("data_buf", &data_buf);
+    pass.draw(shape, data_buf.size());
+  }
+};
+
 /**
  * Contains all overlay generic geometry batches.
  */

source/blender/draw/engines/select/select_empty.hh

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright 2023 Blender Foundation. */
+
+/** \file
+ * \ingroup draw_engine
+ *
+ * Dummy implementation of the select engine types to avoid any overhead.
+ */
+
+#pragma once
+
+#include "draw_manager.hh"
+
+namespace blender::draw::select {
+
+struct EngineEmpty {
+  /* Add type safety to selection ID. Only the select engine should provide them. */
+  struct ID {};
+
+  struct SelectBuf {
+    void select_clear(){};
+    void select_append(ID){};
+    void select_bind(PassSimple &){};
+  };
+
+  struct SelectMap {
+    [[nodiscard]] constexpr ID select_id(const ObjectRef &)
+    {
+      return {};
+    }
+  };
+};
+
+}  // namespace blender::draw::select

source/blender/draw/engines/select/select_object.hh

@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright 2023 Blender Foundation. */
+
+/** \file
+ * \ingroup draw_engine
+ *
+ * This is an implementation of the Select engine specialized for selecting object.
+ * Should plug seamlessly inside the overlay engine logic.
+ */
+
+#pragma once
+
+#include "DRW_gpu_wrapper.hh"
+#include "draw_manager.hh"
+
+namespace blender::draw::select {
+
+struct EngineObject {
+  /* Add type safety to selection ID. Only the select engine should provide them. */
+  struct ID {
+    uint32_t value;
+  };
+
+  /**
+   * Add a dedicated selection id buffer to a pass.
+   * Use this when not using a #PassMain which can pass the select ID via CustomID.
+   */
+  struct SelectBuf {
+    StorageVectorBuffer<uint32_t> select_buf = {"select_buf"};
+
+    void select_clear()
+    {
+      select_buf.clear();
+    }
+
+    void select_append(ID select_id)
+    {
+      select_buf.append(select_id.value);
+    }
+
+    void select_bind(PassSimple &pass)
+    {
+      select_buf.push_update();
+      pass.bind_ssbo("select_buf", &select_buf);
+    }
+  };
+
+  /**
+   * Generate selection IDs from objects and keep record of the mapping between them.
+   */
+  struct SelectMap {
+    uint next_id = 0;
+    Map<uint, ObjectRef> map;
+
+    [[nodiscard]] const ID select_id(const ObjectRef &)
+    {
+      /* TODO Insert Ref into the map. */
+      return {next_id++};
+    }
+  };
+};
+
+}  // namespace blender::draw::select