function _init()
    cam={
        x=12,
        y=12,
        a=0,
        w2d=2
    }
    scrx=0
end

function _update()
    controls()
end

function _draw()
    cls()
    map(0,0,0,0,16,16)
    circ(cam.x,cam.y,2,12)
    --for scrx=0,480 do
    --  raycast(cam,scrx)
    --end
    raycast(cam,240)
end

function controls()
    if btn(0) then
        cam.a+=0.01
    end
    if btn(1) then
        cam.a-=0.01
    end
    if btn(2) then
        cam.x+=cos(cam.a)*0.5
        cam.y+=sin(cam.a)*0.5
    end
    if btn(3) then
        cam.x+=cos(cam.a)*-0.25
        cam.y*=sin(cam.a)*-0.25
    end
end

function raycast(cam,scrx)
    local rayvx,rayvy=
        cam.vx-cam.vy*cam.w2d*(scrx-64)/128,
        cam.vy+cam.vx*cam.w2d*(scrx-64)/128

    -- distance traveled
    local dist=0
    -- current coordinates
    local x,y=cam.x,cam.y
    -- map cel coordinate and value
    local celx,cely=x8,y8
    local cel=mget(celx,cely)
    -- direction of ray
    local dirx,diry=
        sgn(rayvx),sgn(rayvy)

    -- distances across map cel
    local dist4x,dist4y=
        abs(8/rayvx),
        abs(8/rayvy)

    -- distances to next map cel
    local dx,dy=
        abs(4+4*dirx-x%8),
        abs(4+4*diry-y%8)
    local dist2x,dist2y=
        abs(dx/rayvx),
        abs(dy/rayvy)

    -- which direction / angle
    -- the wall was hit from
    local hita=0

    -- perform dda
    repeat

        if dist2x=64
end

-- perform dda
repeat
   if dist2x < dist2y then
      celx+=dirx
      dist+=dist2x
      dist2y-=dist2x
      dist2x=dist4x
      hita=0.25-dirx*0.25
   else
      cely+=diry
      dist+=dist2y
      dist2x-=dist2y
      dist2y=dist4y
      hita=0.5+diry*0.25
   end

   local cel=mget(celx,cely)
   if fget(cel,0) then
      -- ray hit a wall
      rect(celx*8,cely*8,celx*8+7,cely*8+7,12)
   else
      rect(celx*8+2,cely*8+2,celx*8+5,cely*8+5,11)
   end

until dist >= 64