Center logical coordinates (so that zooming in and out keeps center invariant)

src/painter.py

@@ -53,6 +53,17 @@ class Painter(Widget):
         self.undermouse=None
         self.draw()
 
+    # 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
+    def pos_tocoord_y(self,y):
+        return self.height/2+y*Square_element.size
+    def coord_topos_x(self,x):
+        return (x-self.width/2)/Square_element.size
+    def coord_topos_y(self,y):
+        return (y-self.height/2)/Square_element.size
+        
+
 
     # draw all particles
     def draw(self):
@@ -61,7 +72,7 @@ class Painter(Widget):
             # draw order: particles, then grids, then transparent particles
 
             for particle in self.particles:
-                particle.draw()
+                particle.draw(self)
 
             # draw grids
             for particle in self.particles:
@@ -69,8 +80,9 @@ class Painter(Widget):
                     self.draw_grid(particle.squares[0].pos,particle.grid)
 
             for particle in self.particles:
-                particle.draw(alpha=0.5)
+                particle.draw(self,alpha=0.5)
 
+    # draw a grid around a particle
     def draw_grid(self,pos,mesh):
         # height offset due to status bar and command prompt
         height_offset=self.app.status_bar.height+self.app.command_prompt.height
@@ -156,10 +168,13 @@ class Painter(Widget):
     def on_touch_down(self,touch):
         # only respond to touch in drawing area
         if self.collide_point(*touch.pos):
+            # convert to logical
+            touchx=self.coord_topos_x(touch.x)
+            touchy=self.coord_topos_y(touch.y)
 
             # create new cross
             if touch.button=="right":
-                new=Cross(touch.x/Square_element.size,touch.y/Square_element.size)
+                new=Cross(touchx,touchy)
                 if not self.check_interaction_any(new,Point(0,0)):
                     # add to list
                     self.particles.append(new)
@@ -175,11 +190,11 @@ class Painter(Widget):
             # select particle
             if touch.button=="left":
                 # find particle under touch
-                self.undermouse=self.find_particle(Point(touch.x/Square_element.size,touch.y/Square_element.size))
+                self.undermouse=self.find_particle(Point(touchx,touchy))
 
                 # record relative position of click with respect to reference
                 if self.undermouse!=None:
-                    self.offset=Point(touch.x/Square_element.size,touch.y/Square_element.size)-self.undermouse.squares[0].pos
+                    self.offset=Point(touchx,touchy)-self.undermouse.squares[0].pos
 
                 # no modifiers
                 if self.modifiers==[]:
@@ -222,12 +237,16 @@ class Painter(Widget):
 
     # respond to drag
     def on_touch_move(self,touch):
+        # convert to logical
+        touchx=self.coord_topos_x(touch.x)
+        touchy=self.coord_topos_y(touch.y)
+
         # only respond to touch in drawing area
         if self.collide_point(*touch.pos):
             # only move on left click
             if touch.button=="left" and self.modifiers==[] and self.undermouse!=None:
                 # attempted move determined by the relative position to the relative position of click within self.undermouse
-                delta=self.adjust_move(Point(touch.x/Square_element.size,touch.y/Square_element.size)-(self.offset+self.undermouse.squares[0].pos),0)
+                delta=self.adjust_move(Point(touchx,touchy)-(self.offset+self.undermouse.squares[0].pos),0)
                 for particle in self.selected:
                     particle.move(delta)