From 159ac83e8625646b594e0d155df0bb9cdcce281a Mon Sep 17 00:00:00 2001
From: Ian Jauslin <ian@jauslin.org>
Date: Wed, 29 Sep 2021 03:24:23 -0400
Subject: [PATCH] check move

---
 cross.py | 58 +++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 38 insertions(+), 20 deletions(-)

diff --git a/cross.py b/cross.py
index 2d7e397..2b158cf 100644
--- a/cross.py
+++ b/cross.py
@@ -14,7 +14,6 @@ class Cross():
         self.pos=Point(x,y)
         self.color=kwargs.get("color",(0,0,1))
         self.selected=False
-        self.stuckto=None
 
     # set position
     def setpos(self,x,y):
@@ -46,7 +45,19 @@ class Cross():
 
     # check whether a cross at pos interacts with cross
     def check_interaction(self,pos):
-        return (pos-self.pos).int()**2>=5
+        # allow for error
+        return int(pos.x-self.pos.x+sgn(pos.x-self.pos.x)*1e-11)**2+int(pos.y-self.pos.y+sgn(pos.y-self.pos.y)*1e-11)**2>=5
+
+    # check whether a cross at position pos is touching self
+    def check_touch(self,pos):
+        rel=pos-self.pos
+        for i in [-3,-2,-1,1,2,3]:
+            # allow for error
+            if abs(rel.x-i)<1e-11 and abs(rel.y)<=4-abs(i)+1e-11 and abs(rel.y)>=3-abs(i)-1e-11:
+                    return True
+            if abs(rel.y-i)<1e-11 and abs(rel.x)<=4-abs(i)+1e-11 and abs(rel.x)>=3-abs(i)-1e-11:
+                    return True
+        return False
 
     # find position along a line that comes in contact with the line going through pos in direction v
     def move_on_line_to_stick(self,pos,v):
@@ -92,7 +103,7 @@ class Cross():
             closest=self.move_on_line_to_stick_relative(Point(-x.x,x.y),Point(-v.x,v.y))
             return Point(-closest.x,closest.y)
 
-    # move along edge of cross while remaining stuck
+    # move along edge of cross
     def move_along(self,newpos,pos):
         rel=pos-self.pos
         # check if the particle is stuck in the x direction
@@ -220,7 +231,7 @@ class Cross_painter(Widget):
     def on_touch_down(self,touch):
         # create new cross
         if touch.button=="right":
-            if self.check_add(Point(touch.x/Cross.size,touch.y/Cross.size)):
+            if self.check_interaction_any(Point(touch.x/Cross.size,touch.y/Cross.size),None):
                 new=Cross(touch.x/Cross.size,touch.y/Cross.size)
                 with self.canvas:
                     new.draw()
@@ -258,30 +269,37 @@ class Cross_painter(Widget):
         # none found
         return None
 
+    # check whether a position intersects with any of the crosses
+    def check_interaction_any(self,pos,exception):
+        for other in self.crosses:
+            if other!=exception:
+                if other.check_interaction(pos)==False:
+                    return False
+        return True
+
     # check that a cross can move to new position
     def check_move(self,newpos,cross):
+        # whether newpos is acceptable
+        accept_newpos=True
         for other in self.crosses:
             # do not compare a cross to itself
             if other!=cross:
                 # move would make cross overlap with other
                 if other.check_interaction(newpos)==False:
-                    # check if cross is stuck to other
-                    if cross.stuckto==other:
+                    accept_newpos=False
+                    # check if cross touches other
+                    if other.check_touch(cross.pos):
                         # move along other while remaining stuck
-                        return other.move_along(newpos,cross.pos)
+                        candidate=other.move_along(newpos,cross.pos)
                     else:
-                        # stick to the cross
-                        cross.stuckto=other
-                        return other.move_on_line_to_stick(cross.pos,newpos-cross.pos)
-        # reset stuckto if move is allowed
-        cross.stuckto=None
-        return newpos
-
-    # check that a cross can be added at position
-    def check_add(self,pos):
-        for cross in self.crosses:
-            if cross.check_interaction(pos)==False:
-                return False
-        return True
+                        candidate=other.move_on_line_to_stick(cross.pos,newpos-cross.pos)
+                    if self.check_interaction_any(candidate,cross):
+                        return candidate
+        if accept_newpos:
+            return newpos
+        else:
+            # cannot move cross at all, try again
+            return self.check_move(candidate,cross)
+