UI: Drag and Drop Modifiers, Layout Updates

This patch implements the list panel system D7490 for modifiers.
It also moves modifier drawing to a callback in ModifierTypeInfo
in line with the extensible architecture refactoring goal T75724.

This adds a PanelRegister callback and utilities for registering
panels and subpanels. It also adds the callbacks for expansion saving
and drag and drop reordering described in D7490.

These utilities, callbacks, and other common UI elements shared
between modifiers live in MOD_ui_common.c.

Because modifier buttons are now in panels, we can make use of
subpanels for organization. The UI layouts also use the single
column layout style consistently used elsewhere in Blender.
Additionally, the mode-setting buttons are aligned and ordered
consistently with the outliner.

However, the large number of UI changes in this patch may mean
that additional polishing is required in master.

Thanks to William Reynish (@billreynish) who did a fair amount of the
layout work and to Julian Eisel (@Severin) for consistent help.

Differential Revision: https://developer.blender.org/D7498

7 files changed, 157 insertions, 350 deletions

diff --git a/source/blender/editors/include/ED_object.h b/source/blender/editors/include/ED_object.h
index e027efce1d3..cd25ee54392 100644
--- a/source/blender/editors/include/ED_object.h
+++ b/source/blender/editors/include/ED_object.h
@@ -370,12 +370,17 @@ bool ED_object_modifier_remove(struct ReportList *reports,
                                struct Object *ob,
                                struct ModifierData *md);
 void ED_object_modifier_clear(struct Main *bmain, struct Object *ob);
-int ED_object_modifier_move_down(struct ReportList *reports,
-                                 struct Object *ob,
-                                 struct ModifierData *md);
-int ED_object_modifier_move_up(struct ReportList *reports,
-                               struct Object *ob,
-                               struct ModifierData *md);
+bool ED_object_modifier_move_down(struct ReportList *reports,
+                                  struct Object *ob,
+                                  struct ModifierData *md);
+bool ED_object_modifier_move_up(struct ReportList *reports,
+                                struct Object *ob,
+                                struct ModifierData *md);
+bool ED_object_modifier_move_to_index(struct ReportList *reports,
+                                      struct Object *ob,
+                                      struct ModifierData *md,
+                                      const int index);
+
 int ED_object_modifier_convert(struct ReportList *reports,
                                struct Main *bmain,
                                struct Depsgraph *depsgraph,
diff --git a/source/blender/editors/include/UI_interface.h b/source/blender/editors/include/UI_interface.h
index 01bc59f71e7..11dbb105072 100644
--- a/source/blender/editors/include/UI_interface.h
+++ b/source/blender/editors/include/UI_interface.h
@@ -2002,7 +2002,7 @@ void uiTemplatePathBuilder(uiLayout *layout,
                            const char *propname,
                            struct PointerRNA *root_ptr,
                            const char *text);
-uiLayout *uiTemplateModifier(uiLayout *layout, struct bContext *C, struct PointerRNA *ptr);
+void uiTemplateModifiers(uiLayout *layout, struct bContext *C);
 uiLayout *uiTemplateGpencilModifier(uiLayout *layout, struct bContext *C, struct PointerRNA *ptr);
 void uiTemplateGpencilColorPreview(uiLayout *layout,
                                    struct bContext *C,
diff --git a/source/blender/editors/interface/interface_templates.c b/source/blender/editors/interface/interface_templates.c
index 6001e1ea1b5..1d55e2b3e4b 100644
--- a/source/blender/editors/interface/interface_templates.c
+++ b/source/blender/editors/interface/interface_templates.c
@@ -1816,360 +1816,50 @@ void uiTemplatePathBuilder(uiLayout *layout,
 /** \} */
 
 /* -------------------------------------------------------------------- */
-/** \name Modifier Template
+/** \name Modifiers Template
+ *
+ *  Template for building the panel layout for the active object's modifiers.
  * \{ */
 
-#define ERROR_LIBDATA_MESSAGE TIP_("Can't edit external library data")
-
-static void modifiers_convertToReal(bContext *C, void *ob_v, void *md_v)
+static void modifier_panel_id(void *md_link, char *r_name)
 {
-  Object *ob = ob_v;
-  ModifierData *md = md_v;
-  ModifierData *nmd = BKE_modifier_new(md->type);
-
-  BKE_modifier_copydata(md, nmd);
-  nmd->mode &= ~eModifierMode_Virtual;
-
-  BLI_addhead(&ob->modifiers, nmd);
-
-  BKE_modifier_unique_name(&ob->modifiers, nmd);
-
-  ob->partype = PAROBJECT;
-
-  WM_event_add_notifier(C, NC_OBJECT | ND_MODIFIER, ob);
-  DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
-
-  ED_undo_push(C, "Modifier convert to real");
+  ModifierData *md = (ModifierData *)md_link;
+  BKE_modifier_type_panel_id(md->type, r_name);
 }
 
-static bool modifier_can_delete(ModifierData *md)
+void uiTemplateModifiers(uiLayout *UNUSED(layout), bContext *C)
 {
-  /* fluid particle modifier can't be deleted here */
-  if (md->type == eModifierType_ParticleSystem) {
-    short particle_type = ((ParticleSystemModifierData *)md)->psys->part->type;
-    if (ELEM(particle_type,
-             PART_FLUID,
-             PART_FLUID_FLIP,
-             PART_FLUID_FOAM,
-             PART_FLUID_SPRAY,
-             PART_FLUID_BUBBLE,
-             PART_FLUID_TRACER,
-             PART_FLUID_SPRAYFOAM,
-             PART_FLUID_SPRAYBUBBLE,
-             PART_FLUID_FOAMBUBBLE,
-             PART_FLUID_SPRAYFOAMBUBBLE)) {
-      return false;
-    }
-  }
-  return true;
-}
+  ScrArea *sa = CTX_wm_area(C);
+  ARegion *region = CTX_wm_region(C);
 
-/* Check whether Modifier is a simulation or not,
- * this is used for switching to the physics/particles context tab */
-static int modifier_is_simulation(ModifierData *md)
-{
-  /* Physic Tab */
-  if (ELEM(md->type,
-           eModifierType_Cloth,
-           eModifierType_Collision,
-           eModifierType_Fluidsim,
-           eModifierType_Fluid,
-           eModifierType_Softbody,
-           eModifierType_Surface,
-           eModifierType_DynamicPaint)) {
-    return 1;
-  }
-  /* Particle Tab */
-  else if (md->type == eModifierType_ParticleSystem) {
-    return 2;
-  }
-  else {
-    return 0;
-  }
-}
-
-static uiLayout *draw_modifier(uiLayout *layout,
-                               Scene *scene,
-                               Object *ob,
-                               ModifierData *md,
-                               int index,
-                               int cageIndex,
-                               int lastCageIndex)
-{
-  const ModifierTypeInfo *mti = BKE_modifier_get_info(md->type);
-  PointerRNA ptr;
-  uiBut *but;
-  uiBlock *block;
-  uiLayout *box, *column, *row, *sub;
-  uiLayout *result = NULL;
-  int isVirtual = (md->mode & eModifierMode_Virtual);
-  char str[128];
-
-  /* create RNA pointer */
-  RNA_pointer_create(&ob->id, &RNA_Modifier, md, &ptr);
-
-  column = uiLayoutColumn(layout, true);
-  uiLayoutSetContextPointer(column, "modifier", &ptr);
-
-  /* rounded header ------------------------------------------------------------------- */
-  box = uiLayoutBox(column);
-
-  if (isVirtual) {
-    row = uiLayoutRow(box, false);
-    uiLayoutSetAlignment(row, UI_LAYOUT_ALIGN_EXPAND);
-    block = uiLayoutGetBlock(row);
-    /* VIRTUAL MODIFIER */
-    /* XXX this is not used now, since these cannot be accessed via RNA */
-    BLI_snprintf(str, sizeof(str), IFACE_("%s parent deform"), md->name);
-    uiDefBut(block,
-             UI_BTYPE_LABEL,
-             0,
-             str,
-             0,
-             0,
-             185,
-             UI_UNIT_Y,
-             NULL,
-             0.0,
-             0.0,
-             0.0,
-             0.0,
-             TIP_("Modifier name"));
-
-    but = uiDefBut(block,
-                   UI_BTYPE_BUT,
-                   0,
-                   IFACE_("Make Real"),
-                   0,
-                   0,
-                   80,
-                   16,
-                   NULL,
-                   0.0,
-                   0.0,
-                   0.0,
-                   0.0,
-                   TIP_("Convert virtual modifier to a real modifier"));
-    UI_but_func_set(but, modifiers_convertToReal, ob, md);
+  Object *ob;
+  SpaceProperties *sbuts = CTX_wm_space_properties(C);
+  if (sbuts != NULL && (sbuts->pinid != NULL) && GS(sbuts->pinid->name) == ID_OB) {
+    ob = (Object *)sbuts->pinid;
   }
   else {
-    /* REAL MODIFIER */
-    row = uiLayoutRow(box, false);
-    block = uiLayoutGetBlock(row);
-
-    UI_block_emboss_set(block, UI_EMBOSS_NONE);
-    /* Open/Close .................................  */
-    uiItemR(row, &ptr, "show_expanded", 0, "", ICON_NONE);
-
-    /* modifier-type icon */
-    uiItemL(row, "", RNA_struct_ui_icon(ptr.type));
-    UI_block_emboss_set(block, UI_EMBOSS);
-
-    /* modifier name */
-    if (mti->isDisabled && mti->isDisabled(scene, md, 0)) {
-      uiLayoutSetRedAlert(row, true);
-    }
-    uiItemR(row, &ptr, "name", 0, "", ICON_NONE);
-    uiLayoutSetRedAlert(row, false);
-
-    /* mode enabling buttons */
-    UI_block_align_begin(block);
-    /* Collision and Surface are always enabled, hide buttons! */
-    if (((md->type != eModifierType_Collision) || !(ob->pd && ob->pd->deflect)) &&
-        (md->type != eModifierType_Surface)) {
-      uiItemR(row, &ptr, "show_render", 0, "", ICON_NONE);
-      uiItemR(row, &ptr, "show_viewport", 0, "", ICON_NONE);
-
-      if (mti->flags & eModifierTypeFlag_SupportsEditmode) {
-        sub = uiLayoutRow(row, true);
-        if (!(md->mode & eModifierMode_Realtime)) {
-          uiLayoutSetActive(sub, false);
-        }
-        uiItemR(sub, &ptr, "show_in_editmode", 0, "", ICON_NONE);
-      }
-    }
-
-    if (ob->type == OB_MESH) {
-      if (BKE_modifier_supports_cage(scene, md) && (index <= lastCageIndex)) {
-        sub = uiLayoutRow(row, true);
-        if (index < cageIndex || !BKE_modifier_couldbe_cage(scene, md)) {
-          uiLayoutSetActive(sub, false);
-        }
-        uiItemR(sub, &ptr, "show_on_cage", 0, "", ICON_NONE);
-      }
-    } /* tessellation point for curve-typed objects */
-    else if (ELEM(ob->type, OB_CURVE, OB_SURF, OB_FONT)) {
-      /* some modifiers could work with pre-tessellated curves only */
-      if (ELEM(md->type, eModifierType_Hook, eModifierType_Softbody, eModifierType_MeshDeform)) {
-        /* add disabled pre-tessellated button, so users could have
-         * message for this modifiers */
-        but = uiDefIconButBitI(block,
-                               UI_BTYPE_TOGGLE,
-                               eModifierMode_ApplyOnSpline,
-                               0,
-                               ICON_SURFACE_DATA,
-                               0,
-                               0,
-                               UI_UNIT_X - 2,
-                               UI_UNIT_Y,
-                               &md->mode,
-                               0.0,
-                               0.0,
-                               0.0,
-                               0.0,
-                               TIP_("This modifier can only be applied on splines' points"));
-        UI_but_flag_enable(but, UI_BUT_DISABLED);
-      }
-      else if (mti->type != eModifierTypeType_Constructive) {
-        /* constructive modifiers tessellates curve before applying */
-        uiItemR(row, &ptr, "use_apply_on_spline", 0, "", ICON_NONE);
-      }
-    }
-
-    UI_block_align_end(block);
-
-    /* Up/Down + Delete ........................... */
-    UI_block_align_begin(block);
-    uiItemO(row, "", ICON_TRIA_UP, "OBJECT_OT_modifier_move_up");
-    uiItemO(row, "", ICON_TRIA_DOWN, "OBJECT_OT_modifier_move_down");
-    UI_block_align_end(block);
-
-    UI_block_emboss_set(block, UI_EMBOSS_NONE);
-    /* When Modifier is a simulation,
-     * show button to switch to context rather than the delete button. */
-    if (modifier_can_delete(md) && !modifier_is_simulation(md)) {
-      uiItemO(row, "", ICON_X, "OBJECT_OT_modifier_remove");
-    }
-    else if (modifier_is_simulation(md) == 1) {
-      uiItemStringO(
-          row, "", ICON_PROPERTIES, "WM_OT_properties_context_change", "context", "PHYSICS");
-    }
-    else if (modifier_is_simulation(md) == 2) {
-      uiItemStringO(
-          row, "", ICON_PROPERTIES, "WM_OT_properties_context_change", "context", "PARTICLES");
-    }
-    UI_block_emboss_set(block, UI_EMBOSS);
+    ob = CTX_data_active_object(C);
   }
+  ListBase *modifiers = &ob->modifiers;
 
-  /* modifier settings (under the header) --------------------------------------------------- */
-  if (!isVirtual && (md->mode & eModifierMode_Expanded)) {
-    /* apply/convert/copy */
-    box = uiLayoutBox(column);
-    row = uiLayoutRow(box, false);
+  bool panels_match = UI_panel_list_matches_data(region, modifiers, modifier_panel_id);
 
-    if (!ELEM(md->type, eModifierType_Collision, eModifierType_Surface)) {
-      /* only here obdata, the rest of modifiers is ob level */
-      UI_block_lock_set(block, BKE_object_obdata_is_libdata(ob), ERROR_LIBDATA_MESSAGE);
+  if (!panels_match) {
+    UI_panels_free_instanced(C, region);
+    ModifierData *md = modifiers->first;
+    for (int i = 0; md; i++, md = md->next) {
+      const ModifierTypeInfo *mti = BKE_modifier_get_info(md->type);
+      if (mti->panelRegister) {
+        char panel_idname[MAX_NAME];
+        modifier_panel_id(md, panel_idname);
 
-      if (md->type == eModifierType_ParticleSystem) {
-        ParticleSystem *psys = ((ParticleSystemModifierData *)md)->psys;
-
-        if (!(ob->mode & OB_MODE_PARTICLE_EDIT)) {
-          if (ELEM(psys->part->ren_as, PART_DRAW_GR, PART_DRAW_OB)) {
-            uiItemO(row,
-                    CTX_IFACE_(BLT_I18NCONTEXT_OPERATOR_DEFAULT, "Convert"),
-                    ICON_NONE,
-                    "OBJECT_OT_duplicates_make_real");
-          }
-          else if (psys->part->ren_as == PART_DRAW_PATH) {
-            uiItemO(row,
-                    CTX_IFACE_(BLT_I18NCONTEXT_OPERATOR_DEFAULT, "Convert"),
-                    ICON_NONE,
-                    "OBJECT_OT_modifier_convert");
-          }
+        Panel *new_panel = UI_panel_add_instanced(sa, region, &region->panels, panel_idname, i);
+        if (new_panel != NULL) {
+          UI_panel_set_expand_from_list_data(C, new_panel);
         }
       }
-      else {
-        uiLayoutSetOperatorContext(row, WM_OP_INVOKE_DEFAULT);
-        uiItemEnumO(row,
-                    "OBJECT_OT_modifier_apply",
-                    CTX_IFACE_(BLT_I18NCONTEXT_OPERATOR_DEFAULT, "Apply"),
-                    0,
-                    "apply_as",
-                    MODIFIER_APPLY_DATA);
-
-        if (BKE_modifier_is_same_topology(md) && !BKE_modifier_is_non_geometrical(md)) {
-          uiItemEnumO(row,
-                      "OBJECT_OT_modifier_apply",
-                      CTX_IFACE_(BLT_I18NCONTEXT_OPERATOR_DEFAULT, "Apply as Shape Key"),
-                      0,
-                      "apply_as",
-                      MODIFIER_APPLY_SHAPE);
-        }
-      }
-
-      UI_block_lock_clear(block);
-      UI_block_lock_set(block, ob && ID_IS_LINKED(ob), ERROR_LIBDATA_MESSAGE);
-
-      if (!ELEM(md->type,
-                eModifierType_Fluidsim,
-                eModifierType_Softbody,
-                eModifierType_ParticleSystem,
-                eModifierType_Cloth,
-                eModifierType_Fluid)) {
-        uiItemO(row,
-                CTX_IFACE_(BLT_I18NCONTEXT_OPERATOR_DEFAULT, "Copy"),
-                ICON_NONE,
-                "OBJECT_OT_modifier_copy");
-      }
     }
-
-    /* result is the layout block inside the box,
-     * that we return so that modifier settings can be drawn */
-    result = uiLayoutColumn(box, false);
-    block = uiLayoutAbsoluteBlock(box);
   }
-
-  /* error messages */
-  if (md->error) {
-    box = uiLayoutBox(column);
-    row = uiLayoutRow(box, false);
-    uiItemL(row, md->error, ICON_ERROR);
-  }
-
-  return result;
-}
-
-uiLayout *uiTemplateModifier(uiLayout *layout, bContext *C, PointerRNA *ptr)
-{
-  Scene *scene = CTX_data_scene(C);
-  Object *ob;
-  ModifierData *md, *vmd;
-  VirtualModifierData virtualModifierData;
-  int i, lastCageIndex, cageIndex;
-
-  /* verify we have valid data */
-  if (!RNA_struct_is_a(ptr->type, &RNA_Modifier)) {
-    RNA_warning("Expected modifier on object");
-    return NULL;
-  }
-
-  ob = (Object *)ptr->owner_id;
-  md = ptr->data;
-
-  if (!ob || !(GS(ob->id.name) == ID_OB)) {
-    RNA_warning("Expected modifier on object");
-    return NULL;
-  }
-
-  UI_block_lock_set(uiLayoutGetBlock(layout), (ob && ID_IS_LINKED(ob)), ERROR_LIBDATA_MESSAGE);
-
-  /* find modifier and draw it */
-  cageIndex = BKE_modifiers_get_cage_index(scene, ob, &lastCageIndex, 0);
-
-  /* XXX virtual modifiers are not accessible for python */
-  vmd = BKE_modifiers_get_virtual_modifierlist(ob, &virtualModifierData);
-
-  for (i = 0; vmd; i++, vmd = vmd->next) {
-    if (md == vmd) {
-      return draw_modifier(layout, scene, ob, md, i, cageIndex, lastCageIndex);
-    }
-    else if (vmd->mode & eModifierMode_Virtual) {
-      i--;
-    }
-  }
-
-  return NULL;
 }
 
 /** \} */
@@ -2178,6 +1868,8 @@ uiLayout *uiTemplateModifier(uiLayout *layout, bContext *C, PointerRNA *ptr)
 /** \name Grease Pencil Modifier Template
  * \{ */
 
+#define ERROR_LIBDATA_MESSAGE TIP_("Can't edit external library data")
+
 static uiLayout *gpencil_draw_modifier(uiLayout *layout, Object *ob, GpencilModifierData *md)
 {
   const GpencilModifierTypeInfo *mti = BKE_gpencil_modifier_get_info(md->type);
diff --git a/source/blender/editors/object/object_intern.h b/source/blender/editors/object/object_intern.h
index d7a7b4ca110..c5a6e38fbcb 100644
--- a/source/blender/editors/object/object_intern.h
+++ b/source/blender/editors/object/object_intern.h
@@ -162,6 +162,7 @@ void OBJECT_OT_modifier_add(struct wmOperatorType *ot);
 void OBJECT_OT_modifier_remove(struct wmOperatorType *ot);
 void OBJECT_OT_modifier_move_up(struct wmOperatorType *ot);
 void OBJECT_OT_modifier_move_down(struct wmOperatorType *ot);
+void OBJECT_OT_modifier_move_to_index(struct wmOperatorType *ot);
 void OBJECT_OT_modifier_apply(struct wmOperatorType *ot);
 void OBJECT_OT_modifier_convert(struct wmOperatorType *ot);
 void OBJECT_OT_modifier_copy(struct wmOperatorType *ot);
diff --git a/source/blender/editors/object/object_modifier.c b/source/blender/editors/object/object_modifier.c
index 9398a5f2ce7..0bd49f74db9 100644
--- a/source/blender/editors/object/object_modifier.c
+++ b/source/blender/editors/object/object_modifier.c
@@ -430,7 +430,7 @@ void ED_object_modifier_clear(Main *bmain, Object *ob)
   DEG_relations_tag_update(bmain);
 }
 
-int ED_object_modifier_move_up(ReportList *reports, Object *ob, ModifierData *md)
+bool ED_object_modifier_move_up(ReportList *reports, Object *ob, ModifierData *md)
 {
   if (md->prev) {
     const ModifierTypeInfo *mti = BKE_modifier_get_info(md->type);
@@ -440,18 +440,22 @@ int ED_object_modifier_move_up(ReportList *reports, Object *ob, ModifierData *md
 
       if (nmti->flags & eModifierTypeFlag_RequiresOriginalData) {
         BKE_report(reports, RPT_WARNING, "Cannot move above a modifier requiring original data");
-        return 0;
+        return false;
       }
     }
 
     BLI_remlink(&ob->modifiers, md);
     BLI_insertlinkbefore(&ob->modifiers, md->prev, md);
   }
+  else {
+    BKE_report(reports, RPT_WARNING, "Cannot move modifier beyond the start of the list");
+    return false;
+  }
 
-  return 1;
+  return true;
 }
 
-int ED_object_modifier_move_down(ReportList *reports, Object *ob, ModifierData *md)
+bool ED_object_modifier_move_down(ReportList *reports, Object *ob, ModifierData *md)
 {
   if (md->next) {
     const ModifierTypeInfo *mti = BKE_modifier_get_info(md->type);
@@ -461,15 +465,53 @@ int ED_object_modifier_move_down(ReportList *reports, Object *ob, ModifierData *
 
       if (nmti->type != eModifierTypeType_OnlyDeform) {
         BKE_report(reports, RPT_WARNING, "Cannot move beyond a non-deforming modifier");
-        return 0;
+        return false;
       }
     }
 
     BLI_remlink(&ob->modifiers, md);
     BLI_insertlinkafter(&ob->modifiers, md->next, md);
   }
+  else {
+    BKE_report(reports, RPT_WARNING, "Cannot move modifier beyond the end of the list");
+    return false;
+  }
 
-  return 1;
+  return true;
+}
+
+bool ED_object_modifier_move_to_index(ReportList *reports,
+                                      Object *ob,
+                                      ModifierData *md,
+                                      const int index)
+{
+  BLI_assert(md != NULL);
+  BLI_assert(index >= 0);
+  if (index >= BLI_listbase_count(&ob->modifiers)) {
+    BKE_report(reports, RPT_WARNING, "Cannot move modifier beyond the end of the stack");
+    return false;
+  }
+
+  int md_index = BLI_findindex(&ob->modifiers, md);
+  BLI_assert(md_index != -1);
+  if (md_index < index) {
+    /* Move modifier down in list. */
+    for (; md_index < index; md_index++) {
+      if (!ED_object_modifier_move_down(reports, ob, md)) {
+        break;
+      }
+    }
+  }
+  else {
+    /* Move modifier up in list. */
+    for (; md_index > index; md_index--) {
+      if (!ED_object_modifier_move_up(reports, ob, md)) {
+        break;
+      }
+    }
+  }
+
+  return true;
 }
 
 int ED_object_modifier_convert(ReportList *UNUSED(reports),
@@ -1180,6 +1222,60 @@ void OBJECT_OT_modifier_move_down(wmOperatorType *ot)
 /** \} */
 
 /* ------------------------------------------------------------------- */
+/** \name Move to Index Modifier Operator
+ * \{ */
+
+static bool modifier_move_to_index_poll(bContext *C)
+{
+  return edit_modifier_poll(C);
+}
+
+static int modifier_move_to_index_exec(bContext *C, wmOperator *op)
+{
+  Object *ob = ED_object_active_context(C);
+  ModifierData *md = edit_modifier_property_get(op, ob, 0);
+  int index = RNA_int_get(op->ptr, "index");
+
+  if (!ED_object_modifier_move_to_index(op->reports, ob, md, index)) {
+    return OPERATOR_CANCELLED;
+  }
+
+  DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
+  WM_event_add_notifier(C, NC_OBJECT | ND_MODIFIER, ob);
+
+  return OPERATOR_FINISHED;
+}
+
+static int modifier_move_to_index_invoke(bContext *C, wmOperator *op, const wmEvent *UNUSED(event))
+{
+  if (edit_modifier_invoke_properties(C, op)) {
+    return modifier_move_to_index_exec(C, op);
+  }
+  else {
+    return OPERATOR_CANCELLED;
+  }
+}
+
+void OBJECT_OT_modifier_move_to_index(wmOperatorType *ot)
+{
+  ot->name = "Move Active Modifier to Index";
+  ot->description = "Move the active modifier to an index in the stack";
+  ot->idname = "OBJECT_OT_modifier_move_to_index";
+
+  ot->invoke = modifier_move_to_index_invoke;
+  ot->exec = modifier_move_to_index_exec;
+  ot->poll = modifier_move_to_index_poll;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+  edit_modifier_properties(ot);
+  RNA_def_int(
+      ot->srna, "index", 0, 0, INT_MAX, "Index", "The index to move the modifier to", 0, INT_MAX);
+}
+
+/** \} */
+
+/* ------------------------------------------------------------------- */
 /** \name Apply Modifier Operator
  * \{ */
 
diff --git a/source/blender/editors/object/object_ops.c b/source/blender/editors/object/object_ops.c
index 819b6c18a44..05f1ced8615 100644
--- a/source/blender/editors/object/object_ops.c
+++ b/source/blender/editors/object/object_ops.c
@@ -130,6 +130,7 @@ void ED_operatortypes_object(void)
   WM_operatortype_append(OBJECT_OT_modifier_remove);
   WM_operatortype_append(OBJECT_OT_modifier_move_up);
   WM_operatortype_append(OBJECT_OT_modifier_move_down);
+  WM_operatortype_append(OBJECT_OT_modifier_move_to_index);
   WM_operatortype_append(OBJECT_OT_modifier_apply);
   WM_operatortype_append(OBJECT_OT_modifier_convert);
   WM_operatortype_append(OBJECT_OT_modifier_copy);
diff --git a/source/blender/editors/space_buttons/space_buttons.c b/source/blender/editors/space_buttons/space_buttons.c
index c06c107d4a3..187334a5c34 100644
--- a/source/blender/editors/space_buttons/space_buttons.c
+++ b/source/blender/editors/space_buttons/space_buttons.c
@@ -30,8 +30,11 @@
 #include "BLI_utildefines.h"
 
 #include "BKE_context.h"
+#include "BKE_modifier.h"
 #include "BKE_screen.h"
 
+#include "DNA_modifier_types.h"
+
 #include "ED_screen.h"
 #include "ED_space_api.h"
 #include "ED_view3d.h" /* To draw toolbar UI. */
@@ -632,6 +635,15 @@ void ED_spacetype_buttons(void)
 #endif
   BLI_addhead(&st->regiontypes, art);
 
+  /* Register the panel types from modifiers. The actual panels are built per modifier rather than
+   * per modifier type. */
+  for (ModifierType i = 0; i < NUM_MODIFIER_TYPES; i++) {
+    const ModifierTypeInfo *mti = BKE_modifier_get_info(i);
+    if (mti != NULL && mti->panelRegister != NULL) {
+      mti->panelRegister(art);
+    }
+  }
+
   /* regions: header */
   art = MEM_callocN(sizeof(ARegionType), "spacetype buttons region");
   art->regionid = RGN_TYPE_HEADER;