Show approximation of contact zone

collisiontest.p8

@@ -23,7 +23,7 @@ function collides()
 	-- x
 	if ldx==0 then
 		local lx=lx0 -- which ==lx1
-		if (lx<bx0 or lx>=bx1) return false
+		if (lx<bx0 or lx>=bx1) return nil
 	else
  	local tx0=(bx0-lx0)/ldx
  	local tx1=(bx1-lx0)/ldx
@@ -34,7 +34,7 @@ function collides()
  
 	if ldy==0 then
 		local ly=ly0 -- which ==ly1
-		if (ly<by0 or ly>=by1) return false
+		if (ly<by0 or ly>=by1) return nil
 	else
  	local ty0=(by0-ly0)/ldy
  	local ty1=(by1-ly0)/ldy
@@ -43,7 +43,8 @@ function collides()
  	tmax=min(tmax,max(ty0,ty1))
  end 
  
- return tmax>=tmin
+ if (tmax < tmin) return nil
+ return tmin,tmax
 end
 
 
@@ -73,7 +74,7 @@ function _to_halfopen(x0,x1)
 end
 
 function _update60()
- local t=time()/4
+ local t=time()/16
  
 	local bx0_=_bounce_screen(t*1)
 	local by0_=_bounce_screen(t*2)
@@ -117,11 +118,19 @@ end
 function _draw()
  cls(0)
 	rect(bx0,by0,bx1,by1,6)
-	local lc=2
-	if collides() then
-		lc=8
+	line(lx0,ly0,lx1,ly1,2)
+	local cmin, cmax = collides()
+	if cmin then
+	 local dx,dy=lx1-lx0,ly1-ly0
+	 line(lx0 + dx*cmin,
+	      ly0 + dy*cmin,
+	      lx0 + dx*cmax,
+	      ly0 + dy*cmax,
+	      8)
+	 pset(lx0 + dx*cmin,
+	      ly0 + dy*cmin,
+	      10)
 	end
-	line(lx0,ly0,lx1,ly1,lc)
 	
 	pset(last_mx,last_my,7)
 end