Added a few helper methods to mesh add utils.

game/addons/mesh_data_resource_editor/utilities/mesh_add_utils.gd

@@ -1,6 +1,85 @@
 tool
 extends Object
 
+static func get_face_normal_arr_ti(verts : PoolVector3Array, indices : PoolIntArray, triangle_index : int, flipped : bool = false) -> Vector3:
+	return get_face_normal_arr(verts, indices, triangle_index * 3, flipped)
+
+static func get_face_normal_arr(verts : PoolVector3Array, indices : PoolIntArray, index : int, flipped : bool = false) -> Vector3:
+	var v0 : Vector3 = verts[indices[index]]
+	var v1 : Vector3 = verts[indices[index + 1]]
+	var v2 : Vector3 = verts[indices[index + 2]]
+	
+	return get_face_normal(v0, v1, v2, flipped)
+
+static func get_face_normal(v0 : Vector3, v1 : Vector3, v2 : Vector3, flipped : bool = false) -> Vector3:
+	if !flipped:
+		return Plane(v0, v1, v2).normal
+	else:
+		return Plane(v2, v1, v0).normal
+
+static func should_triangle_flip(v0 : Vector3, v1 : Vector3, v2 : Vector3, similar_dir_normal : Vector3) -> bool:
+	var normal : Vector3  = get_face_normal(v0, v1, v2)
+	
+	var ndns : float = normal.dot(similar_dir_normal)
+	
+	return ndns < 0
+
+static func is_normal_similar(v0 : Vector3, v1 : Vector3, v2 : Vector3, similar_dir_normal : Vector3) -> bool:
+	var normal : Vector3  = get_face_normal(v0, v1, v2)
+	
+	var ndns : float = normal.dot(similar_dir_normal)
+	
+	return ndns >= 0
+
+static func flip_triangle_ti(mdr : MeshDataResource, triangle_index : int) -> void:
+	flip_triangle(mdr, triangle_index * 3)
+
+static func flip_triangle(mdr : MeshDataResource, index : int) -> void:
+	var arrays : Array = mdr.get_array()
+	
+	if arrays.size() != ArrayMesh.ARRAY_MAX:
+		arrays.resize(ArrayMesh.ARRAY_MAX)
+		
+	if arrays[ArrayMesh.ARRAY_INDEX] == null:
+		return
+	
+	var indices : PoolIntArray = arrays[ArrayMesh.ARRAY_INDEX]
+
+	var i0 : int = indices[index]
+	var i2 : int = indices[index + 2]
+	
+	indices[index] = i2
+	indices[index + 2] = i0
+
+	arrays[ArrayMesh.ARRAY_INDEX] = indices
+	
+	mdr.set_array(arrays)
+
+static func add_triangle_at(mdr : MeshDataResource, v0 : Vector3, v1 : Vector3, v2 : Vector3, flip : bool = false) -> void:
+	var st : SurfaceTool = SurfaceTool.new()
+	
+	st.begin(Mesh.PRIMITIVE_TRIANGLES)
+
+	st.add_uv(Vector2(0, 1))
+	st.add_vertex(v0)
+	st.add_uv(Vector2(0.5, 0))
+	st.add_vertex(v1)
+	st.add_uv(Vector2(1, 1))
+	st.add_vertex(v2)
+	
+	if !flip:
+		st.add_index(0)
+		st.add_index(1)
+		st.add_index(2)
+	else:
+		st.add_index(2)
+		st.add_index(1)
+		st.add_index(0)
+
+	st.generate_normals()
+	
+	merge_in_surface_tool(mdr, st)
+
 static func add_triangle(mdr : MeshDataResource) -> void:
 	var st : SurfaceTool = SurfaceTool.new()