require "gd"

--[[ This is a demonstration of graphics in Lua,
using the gd library. In this example, we have
hard coded constant data and scale factors to make
the code easier to follow as a "first example"
]]

-- Lua-gd reference manual is at
-- http://lua-gd.luaforge.net/manual.html

-- For demo purposes - data to draw

todraw = [[
Devizes 11000 11009 10975 10902 10793 10653
Warminster 17000 19184 21338 23445 25499 27496
Chippenham 34000 38017 42023 45976 49852 53635
Westbury 11000 12982 14841 16601 18279 19883
Trowbridge 28000 33032 37753 42225 46487 50563
Calne 12000 12263 12411 12466 12446 12366
Dilton_Marsh 2000 2169 2346 2527 2708 2888
Bradford-o-A 9000 9355 9570 9683 9718 9693
Malmesbury 4000 3955 3905 3849 3786 3717
Melksham 22000 24154 26357 28572 30772 32942
Corsham 12000 12897 13849 14831 15826 16822
]]

-- Set up a 450 x 400 pixel image

local image = gd.create(450,400)

-- Allocate the basic colours, and a table of colours
-- for the vectors we will be adding

white = image:colorAllocate(255,255,255)
yellow = image:colorAllocate(255,255,192)
blue = image:colorAllocate(0,0,64)
black = image:colorAllocate(0,0,0)

linecolours = {{96,96,32},{32,128,32},{32,32,128},
        {128,32,32},{0,64,128},{128,64,0},
        {64,0,128},{0,128,64},{128,0,64},
        {64,128,0},{0,192,0},{0,0,192}}

-- Draw the framework

image:fill(0,0,blue)
image:filledRectangle(5,5,444,394,white)
image:filledRectangle(50,50,350,350,yellow)

-- Draw each line of data

town = 0
for line in string.gmatch(todraw,"(.-)\n") do
        town = town + 1
        ccol = linecolours[town]
        colour = image:colorAllocate(ccol[1],
                ccol[2],ccol[3])
        posn = 0
        for val in string.gmatch(line,"%S+") do
                if posn == 0 then
                        place = val
                elseif posn == 1 then
                        starter = tonumber(val)
                        prevval = starter
                else
                        nextval = tonumber(val)
                        x1 = 50 + 300 * (posn - 2) / 5
                        x2 = 50 + 300 * (posn - 1) / 5
                        y1 = 600 - 300 * prevval/starter
                        y2 = 600 - 300 * nextval/starter
                        image:line(x1,y1,x2,y2,colour)
                        prevval = nextval
                end
                posn = posn+1
        end

        -- Offset for Westbury is a kludge to avoid
        -- it overlapping the text for Trowbridge!

        if place == "Westbury" then
        image:string(gd.FONT_SMALL,360,y2-15,place,colour)
        else
        image:string(gd.FONT_SMALL,360,y2-5,place,colour)
        end
end

-- Top and tail the graph

image:string(gd.FONT_LARGE,30,18,
        "Relative Population Growth - North / West Wilts"
        ,black)
image:string(gd.FONT_LARGE,30,370,
        "From 2007 - 2027 - Graph for demonstration only"
        ,black)

-- And save to file

image:jpeg("MyImage.jpg",40)

-- Use jpegStr instead to return a string, then you
-- could use this sort of code to generate graphics
-- from Lua 'on the fly' on a web server.