try this linefill func and start optimizing it

collisiontest.p8

@@ -114,8 +114,9 @@ end
 function _draw()
  cls(0)
 	rect(bx0,by0,bx1,by1,6)
-	quickzot(lx1,ly1,2,lx1-lx0,ly1-ly0,10,9,8)
+	--quickzot(lx1,ly1,2,lx1-lx0,ly1-ly0,10,9,8)
-	--line(lx0,ly0,lx1,ly1,2)
+ linefill(lx0, ly0, lx1, ly1, 2, 9)
+	line(lx0,ly0,lx1,ly1,2)
 	local cmin, cmax = collides()
 	if cmin then
 	 local dx,dy=lx1-lx0,ly1-ly0
@@ -174,6 +175,51 @@ function quickzot(x,y,r,dx,dy,hot,warm,cold)
  end
  rectfill(x-r2,y-r2,x+r2,y+r2,hot)
 end
+
+-- linefill x0 y0 x1 y1 r [col]
+-- draw a thicc line
+-- https://www.lexaloffle.com/bbs/?tid=39016
+function linefill(ax,ay,bx,by,r,c)
+ if(c) color(c)
+ local dx,dy=bx-ax,by-ay
+ -- avoid overflow
+ -- credits: https://www.lexaloffle.com/bbs/?tid=28999
+ local d,n = abs(dx),abs(dy)
+ if (d<n) d,n=n,d
+ n/=d
+ d*=(n*n+1)^0.5
+ if(d<0.001) return
+ local ca,sa=dx/d,-dy/d
+
+ -- polygon points
+ local s={
+  {0,-r},{d,-r},{d,r},{0,r}
+ }
+ local u,v,spans=s[4][1],s[4][2],{}
+ local x0,y0=ax+u*ca+v*sa,ay-u*sa+v*ca
+ for i=1,4 do
+  local u,v=s[i][1],s[i][2]
+  local x1,y1=ax+u*ca+v*sa,ay-u*sa+v*ca
+  local _x1,_y1=x1,y1
+  if(y0>y1) x0,y0,x1,y1=x1,y1,x0,y0
+  local dx=(x1-x0)/(y1-y0)
+  if(y0<0) x0-=y0*dx y0=-1
+  local cy0=y0\1+1
+  -- sub-pix shift
+  x0+=(cy0-y0)*dx
+  for y=y0\1+1,min(y1\1,127) do
+   -- open span?
+   local span=spans[y]
+   if span then
+       rectfill(x0,y,span,y)
+   else
+       spans[y]=x0
+   end
+   x0+=dx
+  end
+  x0,y0=_x1,_y1
+ end
+end
 __gfx__
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