-- Main rendering functions

require "Vector"
local V = Vector

require "Primitives"
local P = Primitives

require "Operations"
local O = Operations

require "Textures"
local T = Textures

local eps = 0.001
local max_dist2 = 30^2
local bg_col = {0.1,0.1,0.1}

local function calculate_normal(sdf, l)
   local delta = eps/10
   return V.new{sdf(l+V.x*delta).dist-sdf(l-V.x*delta).dist,
                sdf(l+V.y*delta).dist-sdf(l-V.y*delta).dist,
                sdf(l+V.z*delta).dist-sdf(l-V.z*delta).dist}/(2*delta)
end

local function march(start, location, ray_dir, sdf, count)
   if V.norm2(location-start) > max_dist2 then
      return bg_col
   end
   
   local p = sdf(location)
   if p.dist < eps then
      return p.texture(location, ray_dir,
                       calculate_normal(sdf, location-(ray_dir*eps)),
                       count, sdf)
   else
      return march(start, location + ray_dir*p.dist,
                   ray_dir, sdf, count+1)
   end
end

local function render(scene, width, height, filename) 
   print("Rendering to file " .. filename .. "...")
   
   local f = io.open(filename, "w")
   f:write("P6 ", width, " ", height, " 255\n")

   local c = scene.camera
   local cam_dir = V.normalize(c.point_at - c.location)
   local right = V.normalize(c.right)
   local up = V.cross(right,cam_dir)
   local aspect = height/width;

   local normalize = V.normalize -- optimization
   
   for y=1,height do
      if y % math.floor(height/10) == 0 then
         print(y/math.floor(height/10) * 10 .. "%")
      end

      local rayy = cam_dir + up*((0.5 - y/height)*c.fov*aspect)

      for x=1,width do
         local ray_dir = normalize(rayy + right*((x/width - 0.5)*c.fov))
         local col = march(c.location, c.location, ray_dir, scene.sdf, 0)
         col = {math.floor(math.min(col[1]*255, 255)),
                math.floor(math.min(col[2]*255, 255)),
                math.floor(math.min(col[3]*255, 255))}

         f:write(string.char(col[1]), string.char(col[2]), string.char(col[3]))
      end
   end

   f:close()

   print("done")
end

Render = {
   eps = eps,
   max_dist2 = max_dist2,
   bg_col = bg_col,
   render = render
}

return Render