diff --git a/chameleonic.p8 b/chameleonic.p8
index 9be5963..fb75cbe 100644
--- a/chameleonic.p8
+++ b/chameleonic.p8
@@ -112,6 +112,73 @@ function _mnmx(x,y)
  return x,y
 end
 
+function _rastn(
+ x0,y0,x1,y1,dx,dy
+)
+ -- todo: more optimized implementation?
+ local iter=_rast(x0,y0,x1,y1)
+ local prevx,prevy=nil,nil
+
+ local done=false
+ return function() 
+  while not done do
+   local x,y=iter()
+
+   if (x==nil) done=true return x1, y1
+
+   local x8 = x\dx
+   local y8 = y\dy
+   if not (x8==prevx and y8==prevy) then 
+    prevx,prevy=x8,y8
+    return x,y
+   end
+  end
+ end
+end
+
+function _rast(
+ x0,y0,x1,y1
+)
+ local dx=abs(x1-x0)
+ local dy=abs(y1-y0)
+ local x=x0
+ local y=y0
+
+ local sx=-1
+ local sy=-1
+ if (x0<x1) sx=1
+ if (y0<y1) sy=1
+	
+ local done=false,err
+ if dx>dy then
+  err=dx/2.0
+  return function()
+   if (done) return 
+   if (x==x1) done=true return x1,y1
+   local oldx,oldy=x,y
+   err-=dy
+   if (err<0) y+=sy err+=dx+dy return oldx,y
+   x+=sx
+   return oldx,oldy
+  end
+ else
+  err=dy/2.0
+  return function()
+   if (done) return
+   if (y==y1) done=true return x1,y1
+   local oldx,oldy=x,y
+   err-=dx
+   if (err<0) x+=sx err+=dy+dx return x,oldy
+   y+=sy
+   return oldx,oldy
+  end
+ end
+end
+
+function _point_eq(p1,p2)
+ return p1.x==p2.x and p1.y==p2.y
+end
+
 -->8
 -- input
 kbd={}
@@ -222,6 +289,7 @@ function level:reinit(n)
  self.todo={}
  self.bigx=(n%8)
  self.bigy=(n\8)
+ self.cache_can_stretch=dcache:new()
 
  self:load_dynobjs()
  self:recollide()
@@ -335,6 +403,7 @@ function level:recollide()
     self._crates[mxy]!=nil
   end
  end
+ self.cache_can_stretch:clear()
 end
 
 function add_adjacent_anchors(tbl,mx,my)
@@ -588,6 +657,75 @@ function level:tug_crate(mx0,my0,dmx,dmy)
  self:recollide()
  self:reanchor(false)
 end
+-->8
+-- collision checks
+function level:can_stretch(
+ p1,p2
+)
+ local key=p1.x..","..p1.y..","..p2.x..","..p2.y
+ return self.cache_can_stretch:wrap(key,function()
+  return self:_can_stretch(p1,p2)
+ end)
+end
+
+function level:_can_stretch(
+ p1,p2
+)
+ -- faster implementation for straight lines
+ if p1.y\8==p2.y\8 then
+  local my=p2.y\8
+  for mx=p1.x\8,p2.x\8 do
+   if (level:mcoll(mx,my)) return false
+  end
+ end
+
+ if p1.x\8==p2.x\8 then
+  local mx=p2.x\8
+  for my=p1.y\8,p2.y\8 do
+   if (level:mcoll(mx,my)) return false
+  end
+ end
+
+ if (level:pcoll(p1.x,p1.y)) return false
+ if (level:pcoll(p2.x,p2.y)) return false
+
+ local res=true
+ for x,y in _rastn(p1.x,p1.y,p2.x,p2.y,8,8) do
+  if level:pcoll(x,y) then
+   res=false
+   break
+  end
+ end
+ 
+ return res
+end
+
+-->8
+--cache impl for collision checks
+dcache={}
+dcache.__index=dcache
+
+function dcache:new()
+ local d={}
+ setmetatable(d,dcache)
+ d:clear()
+ return d
+end
+function dcache:clear()
+ self.old,self.new,self.new_n={},{},0
+end
+
+function dcache:wrap(key,f)
+ local el=self.new[key]
+ if (el!=nil) return el
+ local el=self.old[key]
+ if (el==nil) el=f()
+ self.new[key]=el 
+ self.new_n+=1 
+ if (self.new_n>1000) self.old,self.new,self.new_n=self.new,{},0
+ return el
+end
+
 -->8
 --player handling
 player={}
@@ -905,7 +1043,7 @@ function rope:continue_cast()
  local x1=x0+dx
  local y1=y0+dy
  
- for x,y in self:_rast(
+ for x,y in _rast(
   x0,y0,x1,y1
  ) do
   local latch=
@@ -986,14 +1124,14 @@ function rope:draw(artificial_dx,artificial_dy)
   end
  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*8,9)
+  print(tostr(p.id)..":"..p.x..","..p.y..","..#p.todo,0,i*8,12)
  end
+ --[[
  for _,p in pairs(level._anch) do
 	 pset(p.x,p.y,11)
 	end
@@ -1029,7 +1167,7 @@ function rope:drag(
  local anc=self:_anc(i())
  local busy=self:busy()
 
- for x,y in self:_rast(
+ for x,y in _rast(
   anc.x,anc.y,x,y
  ) do
   local a=self:_anc(i())
@@ -1038,8 +1176,6 @@ function rope:drag(
    a.y=y
    a.dirty=true
    self.dirty=true
-   --self:_find_needed_anchors(i())
-   --self:_find_needed_anchors(i()+1)
    if (not busy) self:_tidy_up_gen()
   end
  end
@@ -1050,7 +1186,7 @@ function rope:make_dirty(only_if_invalid)
  for a=0,#self.ancs do
   local a0=self:_anc(a)
   local a1=self:_anc(a+1)
-  if not self:_can_stretch(a0,a1) then
+  if not level:can_stretch(a0,a1) then
    a0.dirty=true
    a1.dirty=true
    invalid=true
@@ -1075,6 +1211,7 @@ function rope:_tidy_up_gen()
     anc.seen=true
     if self[f](self,a,busy) then
      settled=false anc.changed=true 
+     a=0
     end
    end
    a+=1
@@ -1127,7 +1264,7 @@ function rope:_tidy_up_gen()
  for i=0,#self.ancs do
   local a0=self:_anc(i)
   local a1=self:_anc(i+1)
-  if not self:_can_stretch(a0,a1) then
+  if not level:can_stretch(a0,a1) then
    self:destroy()
   end
  end
@@ -1144,7 +1281,7 @@ function rope:_find_needed_anchors(i,busy)
 
  if (level:pcoll(a2.x,a2.y)) return false
  if (level:pcoll(a0.x,a0.y)) return false 
- if (self:_can_stretch(a0,a2)) return false
+ if (level:can_stretch(a0,a2)) return false
 
  local anchors_bydist={}
  local x0,x2=_mnmx(a0.x,a2.x)
@@ -1156,8 +1293,8 @@ function rope:_find_needed_anchors(i,busy)
 
  for a1 in all(anchors_bydist) do
   a1=a1.el
-  if self:_can_stretch(a0,a1) and
-   self:_can_stretch(a1,a2)
+  if level:can_stretch(a0,a1) and
+   level:can_stretch(a1,a2)
   then
    local id=self.id
    add(self.ancs,{id=id,x=a1.x,y=a1.y,dirty=true,todo={}},i)
@@ -1179,12 +1316,11 @@ function rope:_find_touched_anchors(i)
  if (level:pcoll(a0.x,a0.y)) return false
  if (level:pcoll(a2.x,a2.y)) return false
 
- for bx,by in self:_rast(a0.x,a0.y,a2.x,a2.y) do
+ for bx,by in _rast(a0.x,a0.y,a2.x,a2.y) do
   local a1=level:point_anchor(bx,by)
   if 
    a1!=nil and not _point_eq(a0,a1) and not _point_eq(a1,a2)
    and _linedist(a0,a1,a2)<ELIDE_POINT
-   -- and self:_can_stretch(p,a2)
   then
    local id=self.id
    add(self.ancs,{id=id,x=a1.x,y=a1.y,dirty=true,todo={}},i)
@@ -1212,7 +1348,7 @@ function rope:_elide_point(i,busy)
    return false
   end
 
-  if not self:_can_stretch(a0,a2) then
+  if not level:can_stretch(a0,a2) then
    return false
   end
   
@@ -1233,26 +1369,21 @@ function rope:_elide_point(i,busy)
 end
 
 function rope:_can_move_midpoint(a0,a1_0,a1_1,a2)
- if (level:pcoll(a0.x,a0.y)) return false
- if (level:pcoll(a2.x,a2.y)) return false
- if (level:pcoll(a1_0.x,a1_0.y)) return false
- if (level:pcoll(a1_1.x,a1_1.y)) return false
-
- if not self:_can_stretch(a1_0, a1_1) then
+ if not level:can_stretch(a1_0, a1_1) then
   return false
  end
- if not self:_can_stretch(a0,a1_1) then
+ if not level:can_stretch(a0,a1_1) then
   return false
  end
- if not self:_can_stretch(a1_1,a2) then
+ if not level:can_stretch(a1_1,a2) then
   return false
  end
- for x,y in self:_rastn(a1_0.x,a1_0.y,a1_1.x,a1_1.y,8,8) do
+ for x,y in _rastn(a1_0.x,a1_0.y,a1_1.x,a1_1.y,8,8) do
   local tm={x=x,y=y}
-  if not self:_can_stretch(a0,tm) then
+  if not level:can_stretch(a0,tm) then
    return false
   end
-  if not self:_can_stretch(tm,a2) then
+  if not level:can_stretch(tm,a2) then
    return false
   end
  end
@@ -1304,105 +1435,6 @@ function _line_line(x1,y1,x2,y2,x3,y3,x4,y4)
  return true
 end
 
-function rope:_can_stretch(
- p1,p2
-)
- -- faster implementation for straight lines
- if p1.y\8==p2.y\8 then
-  local my=p2.y\8
-  for mx=p1.x\8,p2.x\8 do
-   if (level:mcoll(mx,my)) return false
-  end
- end
-
- if p1.x\8==p2.x\8 then
-  local mx=p2.x\8
-  for my=p1.y\8,p2.y\8 do
-   if (level:mcoll(mx,my)) return false
-  end
- end
-
- if (level:pcoll(p1.x,p1.y)) return false
- if (level:pcoll(p2.x,p2.y)) return false
-
- local res=true
- for x,y in self:_rastn(p1.x,p1.y,p2.x,p2.y,8,8) do
-  if level:pcoll(x,y) then
-   res=false
-   break
-  end
- end
- 
- return res
-end
-
-function rope:_rastn(
- x0,y0,x1,y1,dx,dy
-)
- -- todo: more optimized implementation?
- local iter=self:_rast(x0,y0,x1,y1)
- local prevx,prevy=nil,nil
-
- local done=false
- return function() 
-  while not done do
-   local x,y=iter()
-
-   if (x==nil) done=true return x1, y1
-
-   local x8 = x\dx
-   local y8 = y\dy
-   if not (x8==prevx and y8==prevy) then 
-    prevx,prevy=x8,y8
-    return x,y
-   end
-  end
- end
-end
-
-function rope:_rast(
- x0,y0,x1,y1
-)
- local dx=abs(x1-x0)
- local dy=abs(y1-y0)
- local x=x0
- local y=y0
-
- local sx=-1
- local sy=-1
- if (x0<x1) sx=1
- if (y0<y1) sy=1
-	
- local done=false,err
- if dx>dy then
-  err=dx/2.0
-  return function()
-   if (done) return 
-   if (x==x1) done=true return x1,y1
-   local oldx,oldy=x,y
-   err-=dy
-   if (err<0) y+=sy err+=dx+dy return oldx,y
-   x+=sx
-   return oldx,oldy
-  end
- else
-  err=dy/2.0
-  return function()
-   if (done) return
-   if (y==y1) done=true return x1,y1
-   local oldx,oldy=x,y
-   err-=dx
-   if (err<0) x+=sx err+=dy+dx return x,oldy
-   y+=sy
-   return oldx,oldy
-  end
- end
-end
-
-function _point_eq(p1,p2)
- return p1.x==p2.x and p1.y==p2.y
-end
-
 function neighbors(p)
  local r={}
  for dx=-1,1,1 do