Set lattice on open

src/painter.py

@@ -51,12 +51,29 @@ class Painter(Widget):
         self.keyboard = Window.request_keyboard(None,self,"text")
         self.keyboard.bind(on_key_down=self.on_key_down,on_key_up=self.on_key_up,on_textinput=self.on_textinput)
 
+        # redraw on resize
+        self.bind(size=lambda obj,value: self.draw())
+
     
     def reset(self):
         self.particles=[]
         self.undermouse=None
         self.draw()
 
+    # set lattice
+    def set_lattice(self,lattice):
+        self.lattice=lattice
+
+        # draw
+        self.draw()
+
+        # snap all existing particles to grid
+        for particle in self.particles:
+            delta=self.lattice.nearest_delta(particle.squares[0].pos)
+            if not self.check_interaction_any(particle,delta):
+                particle.move(delta)
+
+
     # convert logical coordinates (normalized and centered) to the ones that are plotted
     def pos_tocoord_x(self,x):
         return self.width/2+x*Square_element.size