Well, this is closer to right!!

chameleonic.p8

@@ -7,6 +7,10 @@ real_modules={}
 
 frame=0
 function _init()
+ -- cls(0)
+ -- for i in _stepfrom(0.5,-2.5) do print(i) end
+ -- assert(false)
+
  _doall("init") end
 function _update()
  frame+=1
@@ -1096,59 +1100,99 @@ end
 -- TODO: Upon adding a point, start from there to see if we need another
 -- rather than adding at most one
 function rope:_drag1(n1,ax1_new,ay1_new)
- local ax1_old,ay1_old=n1.ax,n1.ay
+ local function _sweep_radar(ax_pivot,ay_pivot,ax_far0,ay_far0,ax_far1,ay_far1)
- local n0=n1.prev
+  if ax_far0==ax_far1 then
+   local ax_far=ax_far0
+   local ax0,ax1=_mnmx(ax_pivot,ax_far)
 
- if n0!=nil then
+   ay_far_old=ay_far0
-  local ax0,ay0=n0.ax,n0.ay
+   for ay_far_new in _stepfrom(ay_far0,ay_far1) do
     for _,anchor in level:anchor_points() do
      if 
-    -- NOTE: Do we need to look at the new path too? Something
+      (ax0<=anchor.ax and anchor.ax<=ax1) and 
-    -- just feels wrong about this check.
+      _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far,ay_far_old)!=
-    -- Really our goal is to figure out if moving the end of the
+      _which_side(anchor.ax,anchor.ay,ax_pivot,ay_pivot,ax_far,ay_far_new)
-    -- path crosses over the anchor, which feels like a point/triangle
-    -- collision
-    -- We also want to pick the anchor that the ray sweeps over first, not
-    -- the closest one. 
-    -- Maybe we should 
-    -- (1) sort by angle difference from the original line
-    -- (2) ignore cases where the angle is not between the two lines
-    -- (3) ignore cases where the created point is further from the original point
-    --     than the _intended_ one would be
-    -- Note that if x or y is held constant, this can be implemented
-    -- with a sort on x or y. For our game this is true.
-    -- 
-    _in_box(anchor.ax,anchor.ay,ax0,ay0,ax1_old,ay1_old) and
-    _which_side(anchor.ax,anchor.ay,ax0,ay0,ax1_old,ay1_old) !=
-    _which_side(anchor.ax,anchor.ay,ax0,ay0,ax1_new,ay1_new)
      then
-    local n05={ax=anchor.ax,ay=anchor.ay,prev=n0,next=n1}
+      return anchor
+     end
+    end
+    ay_far_old=ay_far_new
+   end
+  elseif ay_far0==ay_far1 then
+   local ay_far=ay_far0
+   local ay0,ay1=_mnmx(ay_pivot,ay_far)
+
+   ax_far_old=ax_far0
+   for ax_far_new in _stepfrom(ax_far0,ax_far1) do
+    for _,anchor in level:anchor_points() do
+     if 
+      (ay0<=anchor.ay and anchor.ay<=ay1) and 
+      _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
+    end
+    ax_far_old=ax_far_new
+   end
+  else
+   assert(false, "wtf?")
+  end
+ end
+
+ local ax1_old,ay1_old=n1.ax,n1.ay
+
+ local n0=n1.prev
+ while true do
+  if (n0==nil) break
+  local anch=_sweep_radar(n0.ax,n0.ay,ax1_old,ay1_old,ax1_new,ay1_new)
+  if (anch==nil) break
+  local n05={ax=anch.ax,ay=anch.ay,prev=n0,next=n1}
   n0.next=n05
   n1.prev=n05
-   end
+  n0=n05
-  end
  end
 
  local n2=n1.next
- if n2!=nil then
+ while true do
-  local ax2,ay2=n2.ax,n2.ay
+  if (n2==nil) break
-  for _,anchor in level:anchor_points() do
+  local anch=_sweep_radar(n2.ax,n2.ay,ax1_old,ay1_old,ax1_new,ay1_new)
-   if 
+  if (anch==nil) break
-    _in_box(anchor.ax,anchor.ay,ax1_old,ay1_old,ax2,ay2) and
+  local n15={ax=anch.ax,ay=anch.ay,prev=n1,next=n2}
-    _which_side(anchor.ax,anchor.ay,ax1_old,ay1_old,ax2,ay2) !=
-    _which_side(anchor.ax,anchor.ay,ax1_new,ay1_new,ax2,ay2)
-   then
-    local n15={ax=anchor.ax,ay=anchor.ay,prev=n1,next=n2}
   n1.next=n15
   n2.prev=n15
-   end
+  n2=n15
-  end
  end
 
  n1.ax=ax1_new
  n1.ay=ay1_new
 end
 
+function _stepfrom(x0,x1)
+ local done=false
+ if x0==x1 then
+  return function() 
+   if (done) return nil
+   done=true return x0
+  end
+ end
+
+ local mul=1
+ if (x0>x1) x0,x1,mul=-x0,-x1,-mul
+ local i=flr(x0)
+ local top=flr(x1)
+ return function()
+  if (done) return nil
+  i+=1
+  if i>top then 
+   done = true
+   if (x1!=flr(x1)) return mul*x1
+   return nil
+  end
+  return mul*i
+ end
+end
+
 function _in_box(x,y,x0,y0,x1,y1)
  x0,x1=_mnmx(x0,x1)
  y0,y1=_mnmx(y0,y1)