operators.py

@@ -71,7 +71,7 @@ def draw_lattice_reset(self, context):
 	self.layout.operator(LATTICE_OT_Reset.bl_idname, text="Reset Point Positions", icon='FILE_REFRESH')
 
 classes = [
-    LATTICE_OT_Reset
+	LATTICE_OT_Reset
 ]
 
 def register():

tweak_lattice.py

@@ -35,7 +35,7 @@ def ensure_tweak_lattice_collection(scene: bpy.types.Scene) -> bpy.types.Collect
 
 def ensure_falloff_vgroup(
 		lattice_ob: bpy.types.Object, 
-		vg_name="Group", multiplier=1) -> bpy.types.VertexGroup:
+		vg_name="Group", multiplier=1, expression="x") -> bpy.types.VertexGroup:
 	lattice = lattice_ob.data
 	res_x, res_y, res_z = lattice.points_u, lattice.points_v, lattice.points_w
 
@@ -53,7 +53,11 @@ def ensure_falloff_vgroup(
 
 				coord = Vector((x+2, y+2, z+2))
 				distance_from_center = (coord-center).length
-				influence = 1 - distance_from_center / max_res * 2
+				distance_factor = 1 - (distance_from_center / max_res * 2)
+				try:
+					influence = eval(expression.replace("x", "distance_factor"))
+				except:
+					return None
 
 				vg.add([index], influence * multiplier, 'REPLACE')
 	return vg
@@ -171,6 +175,7 @@ class TWEAKLAT_OT_Create(bpy.types.Operator):
 		# Create some custom properties
 		hook['Lattice'] = lattice_ob
 		hook['Multiplier'] = 1.0
+		hook['Expression'] = 'x'
 
 		rna_idprop_ui_create(
 			hook, "Tweak Lattice", default = 1.0,
@@ -242,15 +247,36 @@ class TWEAKLAT_OT_Falloff(bpy.types.Operator):
 	bl_label = "Adjust Falloff"
 	bl_options = {'REGISTER', 'UNDO', 'INTERNAL'}
 
-	def update(self, context):
+	def update_falloff(self, context):
 		if self.doing_invoke: return
 		hook = context.object
 		lattice_ob = hook['Lattice']
-		ensure_falloff_vgroup(lattice_ob, 'Hook', multiplier=self.multiplier)
+		ret = ensure_falloff_vgroup(lattice_ob, 'Hook', multiplier=self.multiplier, expression=self.expression)
+		self.is_expression_valid = ret != None
+		if ret:
+			hook['Expression'] = self.expression
 		hook['Multiplier'] = self.multiplier
 
+	is_expression_valid: BoolProperty(
+		name = "Error",
+		description = "Used to notify user if their expression is invalid",
+		default = True
+	)
 	# Actual parameters
-	multiplier: FloatProperty(name="Multiplier", default=1, update=update, min=0, soft_max=2)
+	multiplier: FloatProperty(
+		name="Multiplier",
+		description = "Multiplier on the weight values",
+		default=1,
+		update=update_falloff,
+		min=0,
+		soft_max=2
+	)
+	expression: StringProperty(
+		name="Expression",
+		default="x",
+		description = "Expression to calculate the weight values where 'x' is a 0-1 value representing a point's closeness to the lattice center",
+		update=update_falloff,
+	)
 
 	# Storage to share info between Invoke and Update
 	lattice_start_scale: FloatVectorProperty()
@@ -268,6 +294,10 @@ class TWEAKLAT_OT_Falloff(bpy.types.Operator):
 		self.hook_start_scale = hook.scale.copy()
 		lattice_ob = hook['Lattice']
 		self.lattice_start_scale = lattice_ob.scale.copy()
+		if 'Expression' not in hook:
+			# Back-comp for Tweak Lattices created with older versions of the add-on.
+			hook['Expression'] = 'x'
+		self.expression = hook['Expression']
 
 		self.doing_invoke = False
 		wm = context.window_manager
@@ -277,6 +307,12 @@ class TWEAKLAT_OT_Falloff(bpy.types.Operator):
 		layout = self.layout
 		layout.use_property_split = True
 		layout.use_property_decorate = False
+		layout.prop(self, 'expression', text="Expression", slider=True)
+		if not self.is_expression_valid:
+			row = layout.row()
+			row.alert = True
+			row.label(text="Invalid expression.", icon='ERROR')
+
 		layout.prop(self, 'multiplier', text="Strength", slider=True)
 
 	def execute(self, context):