NFT API (ComputerCraft)

-- A simple ComputerCraft API to load and draw NFT files generated by NPaintPro.
-- http://www.computercraft.info/forums2/index.php?/topic/5029-145-npaintpro/

-- Two exposed functions:

-- NFT.load(<String> file)
-- Returns: <table> image

-- NFT.draw(<table> image, <number> xPos, <number> yPos, [<table> terminal object])
-- Draws specified image at specified location.
-- Uses the current terminal if you don't provide a different one.

local blit

if term.blit then
    blit = term.blit
else
    local colNums = {}
    for i = 1, 16 do colNums[("0123456789abcdef"):sub(i, i)] = 2 ^ (i - 1) end

    blit = function(text, fg, bg)
        local first, curText, curFG, curBG = true, {}

        for i = 1, #text do
            local thisChar, thisFG, thisBG = text:sub(i, i), fg:sub(i, i), bg:sub(i, i)

            if thisFG ~= curFG or thisBG ~= curBG then
                if first then first = false else term.write(table.concat(curText)) end

                curText = {}

                if thisFG ~= curFG then
                    curFG = thisFG
                    term.setTextColour(colNums[curFG])
                end

                if thisBG ~= curBG then
                    curBG = thisBG
                    term.setBackgroundColour(colNums[curBG])
                end
            end

            curText[#curText + 1] = thisChar
        end

        term.write(table.concat(curText))
    end
end

function load(file)
    local results = {}

    for line in io.lines(file) do
        local curSkip, curLine, curText, curFG, curBG, readPos, writePos, linePos, fg, bg = 0, {}, {}, {}, {}, 1, 1, 0, "0", " "

        while readPos <= #line do
            local char = line:sub(readPos, readPos)

            if char == "\031" then
                readPos = readPos + 1
                fg = line:sub(readPos, readPos)
                if fg == " " then fg = "f" end
            elseif char == "\030" then
                readPos = readPos + 1
                bg = line:sub(readPos, readPos)
            else
                if bg == " " then
                    curSkip = curSkip + 1

                    if #curText > 0 then
                        curLine[#curLine + 1] = {table.concat(curText), table.concat(curFG), table.concat(curBG)}
                        curText, curFG, curBG, writePos = {}, {}, {}, 1
                    end
                else
                    curText[writePos], curFG[writePos], curBG[writePos] = char, fg, bg
                    writePos = writePos + 1

                    if curSkip > 0 then
                        curLine[#curLine + 1] = linePos
                        curSkip = 0
                    end
                end

                linePos = linePos + 1
            end

            readPos = readPos + 1
        end

        if #curText > 0 then curLine[#curLine + 1] = {table.concat(curText), table.concat(curFG), table.concat(curBG)} end

        results[#results + 1] = curLine
    end

    return results
end

function draw(image, x, y, terminal)
    local oldTerm = terminal and term.redirect(terminal)
    y = y - 1

    for yy = 1, #image do
        local thisLine = image[yy]
        term.setCursorPos(x, y + yy)

        for xx = 1, #thisLine do
            local thisVal = thisLine[xx]

            if type(thisVal) == "number" then
                term.setCursorPos(x + thisVal, y + yy)
            else
                blit(thisVal[1], thisVal[2], thisVal[3])
            end
        end
    end

    if oldTerm then term.redirect(oldTerm) end
end