From af26517c825e69ffa6eec7b9925228ce6644ed6b Mon Sep 17 00:00:00 2001
From: Ian Jauslin <ian@jauslin.org>
Date: Tue, 28 Sep 2021 11:32:24 -0400
Subject: [PATCH] move_on_line_to_stick

---
 main.py | 73 +++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 63 insertions(+), 10 deletions(-)

diff --git a/main.py b/main.py
index b780f44..d34b69f 100644
--- a/main.py
+++ b/main.py
@@ -55,7 +55,7 @@ class Cross_painter(Widget):
                 self.selected.selected=False
 
             # find cross under touch
-            self.selected=self.find_cross((touch.x,touch.y))
+            self.selected=self.find_cross(Point(touch.x,touch.y))
             # select
             if self.selected!=None:
                 self.selected.selected=True
@@ -65,8 +65,7 @@ class Cross_painter(Widget):
     def on_touch_move(self,touch):
         # only move on left click
         if touch.button=="left" and self.selected!=None:
-            #self.selected.pos=self.check_move((touch.x,touch.y),self.selected)
-            self.selected.setpos(touch.x,touch.y)
+            self.selected.pos=self.check_move(Point(touch.x,touch.y),self.selected)
             # redraw
             self.canvas.clear()
             self.draw()
@@ -85,7 +84,9 @@ class Cross_painter(Widget):
         for other in self.crosses:
             # do not compare a cross to itself
             if other!=cross:
-                return newpos
+                if other.check_interaction(newpos)==False:
+                    # stick to the cross
+                    return other.move_on_line_to_stick(cross.pos,newpos-cross.pos)
         return newpos
 
     # check that a cross can be added at position
@@ -105,6 +106,11 @@ class Cross():
         self.color=kwargs.get("color",(0,0,1))
         self.selected=False
 
+    # set position
+    def setpos(self,x,y):
+        self.pos.x=x
+        self.pos.y=y
+
     def draw(self):
         # fill
         #if not self.selected:
@@ -137,8 +143,50 @@ class Cross():
     def check_interaction(self,pos):
         return ((pos-self.pos)/self.size).int()**2>=5
 
-    # find position along a line that comes in contact with the line
-    #def move_on_line_to_stick(self,x,v):
+    # 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):
+        # relative to cross
+        return self.move_on_line_to_stick_relative((pos-self.pos)/self.size,v/self.size)*self.size+self.pos
+    def move_on_line_to_stick_relative(self,x,v):
+
+        # if x is in the right quadrant
+        if abs(x.y)<=x.x:
+            # find all stuck positions on lines
+            stuck=[]
+
+            # check intersections with vertical lines
+            if v.x!=0:
+                for i in range(1,4):
+                    # candidate
+                    y=Point(i,x.y+(i-x.x)*v.y/v.x)
+                    # check that it is in the right range
+                    if abs(y.y)<=4-i and abs(y.y)>=3-i:
+                        stuck.append(y)
+            # check intersections with horizontal lines
+            if v.y!=0:
+                for i in [-3,-2,-1,1,2,3]:
+                    # candidate
+                    y=Point(x.x+(i-x.y)*v.x/v.y,i)
+                    # check that it is in the right range
+                    if y.x<=4-abs(i) and y.x>=3-abs(i):
+                        stuck.append(y)
+
+            return x.closest(stuck)
+
+        # reflect other quadrants to the right one
+        # top quadrant
+        elif abs(x.x)<=x.y:
+            closest=self.move_on_line_to_stick_relative(Point(x.y,x.x),Point(v.y,v.x))
+            return Point(closest.y,closest.x)
+        # bottom quadrant
+        elif abs(x.x)<=-x.y:
+            closest=self.move_on_line_to_stick_relative(Point(-x.y,x.x),Point(-v.y,v.x))
+            return Point(closest.y,-closest.x)
+        # left quadrant
+        else:
+            closest=self.move_on_line_to_stick_relative(Point(-x.x,x.y),Point(-v.x,v.y))
+            return Point(-closest.x,closest.y)
+
 
 class Point:
     def __init__(self,x,y):
@@ -172,10 +220,15 @@ class Point:
     def int(self):
         return Point(int(self.x),int(self.y))
 
-    # set position
-    def setpos(self,x,y):
-        self.x=x
-        self.y=y
+    # find the closest among a list of points
+    def closest(self,points):
+        dist=math.inf
+        closest=None
+        for point in points:
+            if (self-point)**2<dist:
+                closest=point
+                dist=(self-point)**2
+        return closest
 
 # L_infinity distance rescalled by 3 in the x direction
 def cross_distx(x,y):