erase particles

painter.py

@@ -86,6 +86,12 @@ class Painter(Widget):
                 if not 's' in self.modifiers:
                     self.modifiers.append('s')
                     self.modifiers.sort()
+            # remove particles
+            elif keycode[1]=="backspace":
+                for particle in self.selected:
+                    self.particles=remove_fromlist(self.particles,particle)
+                self.selected=[]
+                self.draw()
 
     def on_key_up(self, keyboard, keycode):
         if keycode[1]=="shift":