First version I couldn't immediately break

chameleonic.p8

@@ -1056,6 +1056,38 @@ function rope:draw(artificial_dx,artificial_dy)
    rectfill(x,y-1,x-1,y-3,color)
   end
  end
+ local n1=self.src
+ local sy=0
+ while true do
+  if (n1==nil) break
+  local x=n1.ax*8
+  local y=n1.ay*8
+  rectfill(x-1,y-1,x+1,y+1,12)
+  --print("ax="..n1.ax..",ay="..n1.ay,0,sy)
+  sy+=7
+
+  local n0=n1.prev
+  local n2=n1.next
+  if n0!=nil and n2!=nil then
+   if n1.associated_with then
+    local _,_,_,adx,ady=would_stick(n0.ax,n0.ay,n1.associated_with,n2.ax,n2.ay)
+    assert(adx==-1 or adx==0 or adx==1)
+    assert(ady==-1 or ady==0 or ady==1)
+    --assert(not (adx==0 and ady==0))
+
+    rectfill(x+2,y+2,x+4,y+4,3)
+    pset(x+adx*2,y,9)
+    pset(x,y+ady*2,9)
+   else
+   rectfill(x+2,y+2,x+4,y+4,2)
+   end
+  else
+   rectfill(x+2,y+2,x+4,y+4,4)
+  end
+
+  n1=n1.next
+ end
+
  for _,p in pairs(level._anch) do
 	 pset(p.ax*8,p.ay*8,11)
 	 pset(p.ax*8+p.adx,p.ay*8,11)
@@ -1063,13 +1095,6 @@ function rope:draw(artificial_dx,artificial_dy)
 	end
 
  --[[
- for i=0,#self.ancs+1 do
-  p=self:_anc(i)
-  local c=12
-  if (p.dirty) c=13
-  rectfill(p.x-1,p.y-1,p.x+1,p.y+1,c)
-  print(tostr(p.id)..":"..p.x..","..p.y..","..#p.todo,0,i*8,12)
- end
  print("dirty:"..tostr(self.dirty),32,0,9)
  print("busy:"..tostr(self:busy()),32,7,9)
  print("state:"..tostr(self.state.name),32,14,9)
@@ -1111,31 +1136,9 @@ function rope:_relax()
    local x1,y1=n1.ax,n1.ay
    local x2,y2=n2.ax,n2.ay
 
-   if (x0>x2) x0,y0,x2,y2=x2,y2,x0,y0
+   local would,x1_new,y1_new=would_stick(x0,y0,n1.associated_with,x2,y2)
-
+   if not would then
-   local dx=x2-x0
+    self:_drag(n1,x1_new,y1_new)
-   local dy=y2-y0
-
-   local adx,ady
-   local x1_new,y1_new
-   if abs(dx)>abs(dy) then
-    local dprop=(x1-x0)/dx
-    x1_new,y1_new=x1,y0+dprop*(y2-y0)
-    ady=sgn0(y1_new-y1)
-    adx=0
-    if (y0>y2) adx=ady
-    if (y0<y2) adx=-ady
-   else
-    local dprop=(y1-y0)/dy
-    x1_new,y1_new=x0+dprop*(x2-x0),y1
-    adx=sgn0(x1_new-x1)
-    ady=0
-    if (y0>y2) ady=adx
-    if (y0<y2) ady=-adx
-   end
-
-   if false and (n1.associated_with.adx==-adx or n1.associated_with.ady==-ady) then
-    --self:_drag(n1,x1_new,y1_new)
     n0=n1.prev
     n2=n1.next
     n0.next=n2
@@ -1147,11 +1150,42 @@ function rope:_relax()
  end
 end
 
+function would_stick(x0,y0,anchor,x2,y2)
+ local x1,y1=anchor.ax,anchor.ay
+ if (x0>x2) x0,y0,x2,y2=x2,y2,x0,y0
+
+ local dx=x2-x0
+ local dy=y2-y0
+
+ local adx,ady
+ local x1_new,y1_new
+ if abs(dx)>abs(dy) then
+  local dprop=(x1-x0)/dx
+  x1_new,y1_new=x1,y0+dprop*(y2-y0)
+  ady=sgn0(y1_new-y1)
+  adx=0
+  if (y0>y2) adx=ady
+  if (y0<y2) adx=-ady
+ else
+  local dprop=(y1-y0)/dy
+  x1_new,y1_new=x0+dprop*(x2-x0),y1
+  adx=sgn0(x1_new-x1)
+  ady=0
+  if (y0>y2) ady=adx
+  if (y0<y2) ady=-adx
+ end
+
+ return anchor.adx!=-adx and anchor.ady!=-ady,x1_new,y1_new,adx,ady
+end
+
 -- TODO: Upon adding a point, start from there to see if we need another
 -- rather than adding at most one
 function rope:_drag(n1,ax1_new,ay1_new)
  local function _sweep_radar(ax_pivot,ay_pivot,ax_far0,ay_far0,ax_far1,ay_far1)
   if (ax_far0==ax_far1 and ay_far0==ay_far1) return nil
+  local function crossed(x,y)
+   return x!=y
+  end
 
   if ax_far0==ax_far1 then
    local ax_far=ax_far0
@@ -1161,9 +1195,14 @@ function rope:_drag(n1,ax1_new,ay1_new)
    for ay_far_new in _stepfrom(ay_far0,ay_far1) do
     for _,anchor in level:anchor_points() do
      if 
+      not (anchor.ax==ax_pivot and anchor.ay==ay_pivot) and
+      not (anchor.ax==ax_new and anchor.ay==ay_new) and
       (ax0<=anchor.ax and anchor.ax<=ax1) and 
-      _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far,ay_far_old)!=
+      would_stick(ax_pivot,ay_pivot,anchor,ax_far,ay_far_new) and
-      _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far,ay_far_new)
+      crossed(
+        _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far,ay_far_old),
+        _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far,ay_far_new)
+      )
      then
       return anchor
      end
@@ -1178,11 +1217,14 @@ function rope:_drag(n1,ax1_new,ay1_new)
    for ax_far_new in _stepfrom(ax_far0,ax_far1) do
     for _,anchor in level:anchor_points() do
      if 
-      -- anchor.ax!=ax_pivot and anchor.ay!=ay_pivot and
+      not (anchor.ax==ax_pivot and anchor.ay==ay_pivot) and
-      -- anchor.ax!=ax_new and anchor.ay!=ay_new and
+      not (anchor.ax==ax_new and anchor.ay==ay_new) and
+      would_stick(ax_pivot,ay_pivot,anchor,ax_far_new,ay_far) and
       (ay0<=anchor.ay and anchor.ay<=ay1) and 
-      _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far_old,ay_far)!=
+      crossed(
-      _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far_new,ay_far)
+        _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far_old,ay_far),
+        _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far_new,ay_far)
+      )
      then
       return anchor
      end