From 4a53992c3a3d9c00de9bf2ee56043dfa64d040e0 Mon Sep 17 00:00:00 2001
From: Kistaro Windrider <kistaro@gmail.com>
Date: Sat, 17 Dec 2022 17:43:45 -0800
Subject: [PATCH] Implement levels:anchor_in as a generator.

This gets rid of the (substantial!) overhead of preparing a list and then iterating over it, in exchange for a bit of bookkeeping to simulate the prior behavior of the for loop, which is much cheaper.
---
 chameleonic.p8 | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/chameleonic.p8 b/chameleonic.p8
index 87dfc40..993918b 100644
--- a/chameleonic.p8
+++ b/chameleonic.p8
@@ -270,14 +270,17 @@ function level:anchor_points()
 end
 
 function level:anchors_in(px0,py0,px1,py1)
- ancs={}
- for ax=px0\4,(px1+3)\4 do
-  for ay=py0\4,(py1+3)\4 do
-   local anc=self._anch[_amix(ax,ay)]
-   if (anc!=nil) add(ancs, anc)
+ local anch,ax,xlim,sy,ylim=self._anch,px0\4,(px1+3)\4,py0\4,(py1+3)\4
+ local ay=sy-1
+ return function()
+  while true do
+   ay+=1
+   if(ay>ylim)ay,ax=sy,ax+1
+   if(ax>xlim)return nil
+   local anc=anch[_amix(ax,ay)]
+   if (anc) return anc
   end
  end
- return ancs
 end
 
 function level:get_open_pit(mx,my)
@@ -955,7 +958,7 @@ function rope:_find_needed_anchors(i)
  local anchors_bydist={}
  local x0,x2=_mnmx(a0.x,a2.x)
  local y0,y2=_mnmx(a0.y,a2.y)
- for a1 in all(level:anchors_in(x0-1,y0-1,x2+1,y2+1)) do
+ for a1 in level:anchors_in(x0-1,y0-1,x2+1,y2+1) do
   add(anchors_bydist,{el=a1,key=_linedist(a0,a1,a2)})
  end
  shellsort(anchors_bydist)