-- Textures for raymarcher

require "Vector"
local V = Vector

local function make_phong_texture(lights, mapped_pigment, amb, diff, spec, shiny)
   local normalize = V.normalize

   local eps = 0.0001
   local function light_visibility(location, light_dir, pos, dest, res, sdf)
      local p = sdf(location)
      if pos + p.dist > dest then
         return res
      elseif p.dist < eps then
         return 0.0
      else
         return light_visibility(location + light_dir*p.dist, light_dir, pos+p.dist,
                                 dest, math.min(res, 30*p.dist/(pos+p.dist)), sdf)
      end
   end
   
   return function (location, ray_dir, normal, count, sdf)
      local colour = mapped_pigment(location)
      local thiscol = {colour[1]*amb, colour[2]*amb, colour[3]*amb}

      local reflected_ray = ray_dir - normal*(ray_dir*normal*2)
      for _,light in ipairs(lights) do
         local light_dist = V.norm(light-location)
         local light_dir = (light-location)/light_dist

         local vis = light_visibility(location + light_dir*eps, light_dir, eps, light_dist, 1, sdf)

         local Idiff = math.max(normal*light_dir, 0)
         local Ispec = math.pow(math.max(light_dir*reflected_ray,0),shiny)
            
         thiscol[1] = thiscol[1] + vis*(colour[1]*Idiff*diff + Ispec*spec)
         thiscol[2] = thiscol[2] + vis*(colour[2]*Idiff*diff + Ispec*spec)
         thiscol[3] = thiscol[3] + vis*(colour[3]*Idiff*diff + Ispec*spec)
      end

      return thiscol
   end
end

local function make_count_texture(scale)
   return function (location, ray_dir, normal, count, sdf)
      return {count*scale, count*scale, count*scale}
   end
end

local function make_flat_texture(mapped_pigment)
   return function (location, ray_dir, normal, count, sdf)
      return mapped_pigment(location)
   end
end


-- Pigments

local function make_solid_pigment(colour)
   return function(x,y)
      return colour
   end
end

local function make_checkered_pigment(colour1, colour2)
   return function(x,y)
      if (x%1 < 0.5 and y%1 < 0.5) or (x%1 > 0.5 and y%1 > 0.5) then
         return colour1
      else
         return colour2
      end
   end
end

local function make_mandelbrot_pigment(set_pigment, nonset_pigment, max_iter)

   local function get_col(x,y,cx,cy,iter)
      if iter == 0 then
         return set_pigment(cx, cy)
      elseif x^2 + y^2 > 4 then
         return nonset_pigment(cx, cy)
      else
         return get_col(x^2 - y^2 + cx,
                        2*x*y + cy,
                        cx, cy, iter-1)
      end
   end

   return function (x,y)
      return get_col(0,0,x,y,max_iter)
   end
end

-- Mapping functions

-- These functions define mappings from 3D world coordinates to 2D
-- texture/pigment coordinates

local function map_rectangular(pigment, xvec, yvec)
   return function(location)
      return pigment(location*xvec, location*yvec)
   end
end

local function map_spherical(pigment, centre, scale_theta, scale_phi)
   return function(location)
      local r = location-centre
      local rnorm = V.norm(r)
      
      local phi = math.acos((V.z*r)/rnorm)
      local theta = math.acos((V.x*r)/V.norm(V.cross(V.z,r)))

      return pigment(theta*scale_theta/math.pi, phi*scale_phi/math.pi)
   end
end
   
Textures = {
   make_phong_texture = make_phong_texture,
   make_flat_texture = make_flat_texture,
   make_count_texture = make_count_texture,
   make_solid_pigment = make_solid_pigment,
   make_checkered_pigment = make_checkered_pigment,
   make_mandelbrot_pigment = make_mandelbrot_pigment,
   map_rectangular = map_rectangular,
   map_spherical = map_spherical
}

return Textures