CC Pixel API

-- Pixel API
-- by SukaiPoppuGo
--
-- Draw graphics with square pixels, without color restriction
--
-- # Graphic resolution:
-- Graphic size -> 9 pixels wide, 9 pixels high
-- Result on screen -> 9 char wide, 6 lines high
--
-- # Graphic table format
-- Set of lines.
-- Each line is a string, whose chars correspond to a pixel.
-- A pixel is a char set in [0-9a-f], as color reference (see term.blit and colors API)
-- Transparent pixels could be written by space " ", and stand for terminal background color
--
--
-- # Usage
--
-- ## Compute graphics from NFP file
--
-- local oCG = pixel.load("gfx/icon.nfp")
--
-- ## Compute graphics from table
--
local brand = {
    "0123  00000   0               0 ",
    "4567  0    0                  0 ",
    "89ab  00000   0  0   0  000   0 ",
    "cdef  0       0   0 0  0   0  0 ",
    "      0       0    0   00000  0 ",
    "      0       0   0 0  0      0 ",
    "      0       0  0   0  0000   0"
}
-- local oCG = pixel.compute(brand)
--
-- ## Draw graphics
--
-- term.setCursorPos(2, 2)
-- pixel.draw( oCG )
--
-- ## Draw graphics on a monitor
--
-- local monitor = peripheral.find("monitor")
-- local oCG = pixel.load("gfx/icon.nfp", monitor)
-- monitor.setCursorPos(2, 2)
-- pixel.draw( oCG, monitor )
--

-- Colors references
local _colors = {
    [    1] = "0", -- white
    [    2] = "1", -- orange
    [    4] = "2", -- magenta
    [    8] = "3", -- lightBlue
    [   16] = "4", -- yellow
    [   32] = "5", -- lime
    [   64] = "6", -- pink
    [  128] = "7", -- gray
    [  256] = "8", -- lightGray
    [  512] = "9", -- cyan
    [ 1024] = "a", -- purple
    [ 2048] = "b", -- blue
    [ 4096] = "c", -- brown
    [ 8192] = "d", -- green
    [16384] = "e", -- red
    [32768] = "f", -- black
}

local _grayScale = {
    ["0"] = "0", -- white
    ["1"] = "8", -- orange
    ["2"] = "8", -- magenta
    ["3"] = "8", -- lightBlue
    ["4"] = "8", -- yellow
    ["5"] = "8", -- lime
    ["6"] = "8", -- pink
    ["7"] = "7", -- gray
    ["8"] = "8", -- lightGray
    ["9"] = "7", -- cyan
    ["a"] = "7", -- purple
    ["b"] = "7", -- blue
    ["c"] = "7", -- brown
    ["d"] = "7", -- green
    ["e"] = "7", -- red
    ["f"] = "f", -- black
}

local function conv(ref, oTarget)
    local C = oTarget.isColor() and ref or _grayScale[ ref ]
    return C or " "
end

-- Combine odd and even chars
local function getChar(C, line_a, line_b, x, bg, outputLine, oTarget)
    local pix_a = line_a and conv(line_a:sub(x,x), oTarget) or bg
    local pix_b = line_b and conv(line_b:sub(x,x), oTarget) or bg
    pix_a = (pix_a == " " or pix_a == "") and bg or pix_a
    pix_b = (pix_b == " " or pix_b == "") and bg or pix_b
    C = (pix_a == pix_b) and " " or C
    return {
        outputLine[1]..C,
        outputLine[2]..pix_a,
        outputLine[3]..pix_b
    }
end

-- pixel.compute( tGraphics [, oTarget ] )
-- Compute graphic from a table
-- param    table   tGraphics   Table of pixel lines
-- param    object  oTarget Terminal object
-- retrun   object  oCG     Computed graphics
function compute(tGraphics, oTarget)
    local mon = oTarget or term

    local output = {}
    local bg = _colors[mon.getBackgroundColor()]

    for cy=1,#tGraphics,3 do
        local oddLine, evenLine = {"","",""}, {"","",""}
        local length = math.max(
            tGraphics[cy]   and string.len(tGraphics[cy]) or 0,
            tGraphics[cy+1] and string.len(tGraphics[cy+1]) or 0,
            tGraphics[cy+3] and string.len(tGraphics[cy+2]) or 0
        )
        for cx=1,length do
            oddLine = getChar("\143", tGraphics[cy], tGraphics[cy+1], cx, bg, oddLine, mon)
            if tGraphics[cy+1] then
                evenLine = getChar("\131", tGraphics[cy+1], tGraphics[cy+2], cx, bg, evenLine, mon)
            else
                evenLine = false
            end
        end
        table.insert(output, {oddLine[1], oddLine[2], oddLine[3]})
        if evenLine then
            table.insert(output, {evenLine[1], evenLine[2], evenLine[3]})
        end
    end

    return output
end

-- pixel.loadFile( tGraphics [, oTarget ] )
-- Compute NFP file (Graphics files from paint program)
-- param    string  sPath   Path to NFP file
-- param    object  oTarget Terminal object
-- retrun   object  oCG     Computed graphics
function loadFile(sPath, oTarget)
    local mon = oTarget or term

    local contents, line = {}
    local handler = fs.open(sPath, "r")
    while true do
        line = handler.readLine()
        if line then
            table.insert(contents, line)
        else
            handler.close()
            return compute(contents, mon)
        end
    end
end

-- pixel.draw( oCG [, oTarget ] )
-- param    table   oCG     Computed graphics object (get from pixel.compute() or pixel.loadFile())
-- param    object  oTarget Terminal object
function draw(oCG, oTarget)
    local mon = oTarget or term

    local x, y = mon.getCursorPos()

    for _, line in pairs(oCG) do
        mon.setCursorPos(x,y)
        mon.blit( unpack(line) )
        y = y+1
    end
end

local demo = ...
if demo == "demo" then
    local oCG = compute(brand)
    term.setCursorPos(2,1)
    term.clear()
    print("Pixel API demo")
    term.setCursorPos(2,2)
    draw( oCG )
    print("")
end