POINTONSLOPE pico-8

function pointonslope(x,y)
 --returns true if x,y overlaps
 --some slope

 spriteid=mget(flr8(x),flr8(y))

 if not fget(spriteid,1) then
  --tile isn't a slope
  return false
 end

 --define slope of tile
 x1=flr8(x)*8
 x2=x1+8
 y1=flr8(y)*8+8
 y2=y1-8

 if fget(spriteid,2) then
  --halfstep up
  y2=y1-4
 end
 if fget(spriteid,3) then
  --halfstep up 2
  y1-=4
  y2-=1
 end
 if fget(spriteid,4) then
  --fullstep up
  --this is default so eh
  y2-=1
 end
 if fget(spriteid,5) then
  --fullstep down
  y1=y2
  y2+=8
  y1-=1
 end
 if fget(spriteid,6) then
  --halfstep down 2
  y1=y2
  y2+=4
  y1-=1
 end
 if fget(spriteid,7) then
  --halfstep down
  y2=y1
  y1-=4
 end

 --now check if x,y is below
 --the line between p1 and p2
 t=(x2-x)/8


 height=lerp(y2,y1,t)
 if (height<=y) return true


 return false

end

function flr8(v)
 --converts a position from
 --game space to map space
 return flr(v/8)
end

function lerp(a,b,t)
 return (1-t)*a+t*b
end