[Lua] STL to OBJ

--[[
    Convert ASCII STL file to OBJ (wavefront file) with optional coloring
    V 1.0
--]]

local version = "1.0"

print("Usage:")
print("stl_to_obj.lua <stl_file> [<color>]")
print("-----------")
print("<color>: can be a color: red,green,blue,cyan,magenta,yellow")
print("<color>: can be and RGB value R,G,B: 255,70,80")

--/////////////////////////////////////////////////////////////////
-- input stl filename
local stl_filename = arg[1]
local filename = string.sub(stl_filename,1,-5)

print()
print("Input file: "..stl_filename)

local color_rgb = {
    ["red"] = {1.0,0,0},
    ["green"] = {0,1.0,0},
    ["blue"] = {0,0,1.0},
    ["cyan"] = {0,1.0,1.0},
    ["magenta"] = {1.0,0,1.0},
    ["yellow"] = {1.0,1.0,0},
}

local color = {}
if arg and arg[2] then
    if color_rgb[arg[2]] then
        color = color_rgb[arg[2]]
    else
        local r,g,b = string.match(arg[2],"(%d+),(%d+),(%d+)")
        color = {tonumber(r)/255,tonumber(g)/255,tonumber(b)/255}
    end
    print("Input color: "..arg[2])
end




-- obj filename
local obj_filename = filename..".obj"
print("Output file: "..obj_filename)

local t_vertices = {}
local t_normals = {}
local t_faces = {}

--/////////////////////////////////////////////////////////////////
-- parse stl file
local file_stl = io.open(stl_filename, "r")

local cur_face = {}
local count = 0
for line in file_stl:lines() do
    if string.find(line, "^%s*facet normal") then
        local x,y,z = string.match(line, "(%S+)%s(%S+)%s(%S+)$")
        table.insert(cur_face, {tonumber(x),tonumber(y),tonumber(z)})
    end
    if string.find(line, "^%s*vertex") then
        local x,y,z = string.match(line, "(%S+)%s(%S+)%s(%S+)$")
        table.insert(cur_face, {tonumber(x),tonumber(y),tonumber(z)})
        count = count + 1
        if count == 3 then
            table.insert(t_faces,cur_face)
            cur_face = {}
            count = 0
        end
    end
end
file_stl:close()

--/////////////////////////////////////////////////////////////////
-- write mtl
local mtl_filename = filename..".mtl"
if #color ~= 0 then
    print("Output mtl: "..mtl_filename)
    local file = io.open(mtl_filename, "w")
    file:write(
        "# Color: "..arg[2].."\n"..
        "newmtl color_"..arg[2].."\n"..
        "Ka "..string.format("%f",color[1]).." "..string.format("%f",color[2]).." "..string.format("%f",color[3]).."\n"..
        "Kd "..string.format("%f",color[1]).." "..string.format("%f",color[2]).." "..string.format("%f",color[3]).."\n"..
        "Ks 0.000 0.000 0.000\n")
    file:close()
end

print()

--/////////////////////////////////////////////////////////////////
-- write obj
local file = io.open(obj_filename, "w")

file:write("#########################################\n")
file:write("# Wavefront .obj file\n")
file:write("# Created by: stl_to_obj.lua (v "..version..") / Author: Michael Lutz\n")
file:write("# Date: "..os.date().."\n")
file:write("#########################################\n\n")

if #color ~= 0 then
    file:write("#########################################\n")
    file:write("# MTL lib:\n\n")
    file:write("mtllib "..mtl_filename.."\n\n")
end

--/////////////////////////////////////////////////////////////////
-- # List of Vertices
file:write("#########################################\n")
file:write("# List of vertices:\n\n")

for i,v in ipairs(t_faces) do
    for i2=2,4 do
        file:write("v "..string.format("%f",v[i2][1]).." "..string.format("%f",v[i2][2]).." "..string.format("%f",v[i2][3]).."\n")
    end
end
file:write("\n")

--/////////////////////////////////////////////////////////////////
--# Normals in (x,y,z) form; normals might not be unit.
-- Normals are not needed since stl saves the triangles in counter clock anyways
--file:write("\n# List of Normals\n\n")
--for i,v in ipairs(t_faces) do
--  file:write("vn "..string.format("%f",v[1][1]).." "..string.format("%f",v[1][2]).." "..string.format("%f",v[1][3]).."\n")
--end

--/////////////////////////////////////////////////////////////////
-- # Face Definitions (see below)
file:write("#########################################\n")
file:write("# Face definitions:\n\n")


if #color ~= 0 then
    file:write("usemtl color_"..arg[2].."\n\n")
end

for i,v in ipairs(t_faces) do
    local i2 = (i-1)*3
    --file:write("f "..(i2+1).."//"..i.." "..(i2+2).."//"..i.." "..(i2+3).."//"..i.."\n")
    file:write("f "..(i2+1).." "..(i2+2).." "..(i2+3).."\n")
end

file:close()