UI: Grease Pencil Modifier Drag and Drop, Layout Changes

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

This also adds the "set_error" function for grease pencil modifiers,
which hadn't been copied from mesh modifiers yet.

The implementation is basically exactly the same as for the modifier
patch (9b099c86123fc82).

Thanks to Matias Mendiola (mendio) for providing mockups for many
of the layout changes.

Differential Revision: https://developer.blender.org/D7978

3 files changed, 90 insertions, 0 deletions

diff --git a/source/blender/editors/object/object_gpencil_modifier.c b/source/blender/editors/object/object_gpencil_modifier.c
index 6d0f53cfa1e..99215686280 100644
--- a/source/blender/editors/object/object_gpencil_modifier.c
+++ b/source/blender/editors/object/object_gpencil_modifier.c
@@ -211,6 +211,40 @@ int ED_object_gpencil_modifier_move_down(ReportList *UNUSED(reports),
   return 1;
 }
 
+bool ED_object_gpencil_modifier_move_to_index(ReportList *reports,
+                                              Object *ob,
+                                              GpencilModifierData *md,
+                                              const int index)
+{
+  BLI_assert(md != NULL);
+  BLI_assert(index >= 0);
+  if (index >= BLI_listbase_count(&ob->greasepencil_modifiers)) {
+    BKE_report(reports, RPT_WARNING, "Cannot move modifier beyond the end of the stack");
+    return false;
+  }
+
+  int md_index = BLI_findindex(&ob->greasepencil_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_gpencil_modifier_move_down(reports, ob, md)) {
+        break;
+      }
+    }
+  }
+  else {
+    /* Move modifier up in list. */
+    for (; md_index > index; md_index--) {
+      if (!ED_object_gpencil_modifier_move_up(reports, ob, md)) {
+        break;
+      }
+    }
+  }
+
+  return true;
+}
+
 static int gpencil_modifier_apply_obdata(
     ReportList *reports, Main *bmain, Depsgraph *depsgraph, Object *ob, GpencilModifierData *md)
 {
@@ -596,6 +630,60 @@ void OBJECT_OT_gpencil_modifier_move_down(wmOperatorType *ot)
   gpencil_edit_modifier_properties(ot);
 }
 
+/* ************************* Move to Index Gpencil Modifier Operator ************************* */
+
+static bool gpencil_modifier_move_to_index_poll(bContext *C)
+{
+  return gpencil_edit_modifier_poll(C);
+}
+
+static int gpencil_modifier_move_to_index_exec(bContext *C, wmOperator *op)
+{
+  Object *ob = ED_object_active_context(C);
+  GpencilModifierData *md = gpencil_edit_modifier_property_get(op, ob, 0);
+  int index = RNA_int_get(op->ptr, "index");
+
+  if (!ED_object_gpencil_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 gpencil_modifier_move_to_index_invoke(bContext *C,
+                                                 wmOperator *op,
+                                                 const wmEvent *UNUSED(event))
+{
+  if (gpencil_edit_modifier_invoke_properties(C, op)) {
+    return gpencil_modifier_move_to_index_exec(C, op);
+  }
+  else {
+    return OPERATOR_CANCELLED;
+  }
+}
+
+void OBJECT_OT_gpencil_modifier_move_to_index(wmOperatorType *ot)
+{
+  ot->name = "Move Active Modifier to Index";
+  ot->idname = "OBJECT_OT_gpencil_modifier_move_to_index";
+  ot->description =
+      "Change the modifier's position in the list so it evaluates after the set number of "
+      "others";
+
+  ot->invoke = gpencil_modifier_move_to_index_invoke;
+  ot->exec = gpencil_modifier_move_to_index_exec;
+  ot->poll = gpencil_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);
+}
+
 /************************ apply modifier operator *********************/
 
 static int gpencil_modifier_apply_exec(bContext *C, wmOperator *op)
diff --git a/source/blender/editors/object/object_intern.h b/source/blender/editors/object/object_intern.h
index 1cd91f7c1f3..8feeb3b6067 100644
--- a/source/blender/editors/object/object_intern.h
+++ b/source/blender/editors/object/object_intern.h
@@ -190,6 +190,7 @@ void OBJECT_OT_gpencil_modifier_add(struct wmOperatorType *ot);
 void OBJECT_OT_gpencil_modifier_remove(struct wmOperatorType *ot);
 void OBJECT_OT_gpencil_modifier_move_up(struct wmOperatorType *ot);
 void OBJECT_OT_gpencil_modifier_move_down(struct wmOperatorType *ot);
+void OBJECT_OT_gpencil_modifier_move_to_index(struct wmOperatorType *ot);
 void OBJECT_OT_gpencil_modifier_apply(struct wmOperatorType *ot);
 void OBJECT_OT_gpencil_modifier_copy(struct wmOperatorType *ot);
 
diff --git a/source/blender/editors/object/object_ops.c b/source/blender/editors/object/object_ops.c
index 84bc10f8064..1060a808cfe 100644
--- a/source/blender/editors/object/object_ops.c
+++ b/source/blender/editors/object/object_ops.c
@@ -152,6 +152,7 @@ void ED_operatortypes_object(void)
   WM_operatortype_append(OBJECT_OT_gpencil_modifier_remove);
   WM_operatortype_append(OBJECT_OT_gpencil_modifier_move_up);
   WM_operatortype_append(OBJECT_OT_gpencil_modifier_move_down);
+  WM_operatortype_append(OBJECT_OT_gpencil_modifier_move_to_index);
   WM_operatortype_append(OBJECT_OT_gpencil_modifier_apply);
   WM_operatortype_append(OBJECT_OT_gpencil_modifier_copy);