-- Textures for raymarcher

require "Vector"
local V = Vector

require "Colours"
local C = Colours

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 vis = 1.0

         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(pigment1, pigment2)
   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 pigment1(x,y)
      else
         return pigment2(x,y)
      end
   end
end

local function make_image_pigment(filename,scale)

   print("Loading image pigmant from '" .. filename .. "'...")

   local f = assert(io.open(filename, "rb"))
   local data = f:read("*all")
   f:close()

   local start,_,wstr,hstr,dstr,raster =
      string.find(data, "^P6[%s%c]+(%d+)[%s%c]+(%d+)[%s%c]+(%d+)[%s%c](.*)$")

   if start ~= 1 then
      error("Error reading image. Is it in PPM(P6) format?")
   end

   if dstr ~= "255" then
      error("Only images with a depth of 255 are supported.")
   end

   local width = tonumber(wstr)
   local height = tonumber(hstr)
   local depth = tonumber(dstr)

   local pixels = {}
   local i = 1
   for triple in string.gmatch(raster, "...") do
      local _,_,r,g,b = string.find(triple, "(.)(.)(.)")
      pixels[i] = {string.byte(r)/depth, string.byte(g)/depth, string.byte(b)/depth}
      i = i + 1
   end
   
   print("done.")
   print("(Read " .. tostring(#pixels) .. " pixels.)")

   local pixels_per_unit = math.max(width,height)

   return function(x,y)
      local xi = math.floor(((x+0.5)*pixels_per_unit/scale)%width) + 1
      local yi = math.floor(((y+0.5)*pixels_per_unit/scale)%height) + 1
      local i = width*(yi-1) + xi
      if pixels[i] == nil then
         error("Pixel not found at xi=" .. tostring(xi) .. " yi=" .. tostring(yi))
      end
      return pixels[i]
   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

local function make_rainbow_pigment(scale)
   return function (x,y)

      local Ired = math.sin(x/math.pi/scale)^2 * math.sin(y/math.pi/scale)^2
      local Igreen = math.cos(x/math.pi/scale)^2 * math.sin(y/math.pi/scale)^2
      local Iblue = math.sin(x/math.pi/scale)^2 * math.cos(y/math.pi/scale)^2

      return C.red*Ired + C.green*Igreen + C.blue*Iblue
   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_image_pigment = make_image_pigment,
   make_rainbow_pigment = make_rainbow_pigment,
   make_mandelbrot_pigment = make_mandelbrot_pigment,
   map_rectangular = map_rectangular,
   map_spherical = map_spherical
}

return Textures