ComputerCraft TextImage

-- ComputerCraft Screen Resolution: 51 x 19
-- Out of this, we should be only using 51 x 18, leaving one row at the top or bottom
-- This leaves us with 918 pixels in total to store.

-- Since a computercraft screen is 624x354 large...
-- We can assume that each ComputerCraft "pixel" is actually 12.235294117647 x 18.631578947368 large.
-- Or not... Each screen character/pixel is actually 6x9.
-- What this means that we have 51*6 x 19*9 screens... in other words, 306 x 171.

-- Therefore, when we want to display pictures, we have to first fit it to the same aspect ratio as 306 x 171, then squeeze it down to 51 x 19.

os.loadAPI("corefunc")

function GetCoords(number,max_y) -- the maximum of Y (number of rows) is irrelevant to us. We only need to know how many columns are there.
    local x = math.ceil(number/max_y)
    local y = number % max_y
    if y == 0 then
        y = max_y
    end
    return x,y
end

function TransCord(x,y,max_y) -- the maximum of X (number of rows) is once again, irrelevant to us. We only need to know how many columns are there.
    return ((x*max_y)+y)
end

-- These two functions are going to be important to us later on.

function PrintBwImage(bits,max_y) -- Black and white, 1-bit image
    term.clear()
    for key,value in ipairs(bits) do
        local pos_y,pos_x = GetCoords(key,max_y)
        term.setCursorPos(pos_x,pos_y)
        if value == true then
            term.setBackgroundColor(colors.white)
        else
            term.setBackgroundColor(colors.black)
        end
        term.write(" ")
    end
    term.setBackgroundColor(colors.black)
    term.setTextColor(colors.white)
end

function PrintCdImage(hexes,max_y) -- Coloured image. Unfortunately, ComputerCraft uses 16-bit integers for the 16 colours. Very wasteful, but fortunately I found a way to get around it.
    term.clear()
    for key,value in ipairs(hexes) do
        local pos_y,pos_x = GetCoords(key,max_y)
        term.setCursorPos(pos_x,pos_y)
        term.setBackgroundColor(math.pow(2,value))
        term.write(" ")
    end
    term.setBackgroundColor(colors.black)
    term.setTextColor(colors.white)
end

-- Here come "interlaced" images, which have backgrounds and foregrounds!

local grey = '\127'

function PrintGrImage(bits,max_y) -- Greyscale dithered image, with black, white, light grey and dakr grey.
    term.clear()
    local length = math.ceil(#bits/2)
    for i=1,length do
        local pos_y,pos_x = GetCoords(i,max_y)
        term.setCursorPos(pos_x,pos_y)
        if bits[(i*2)-1] == true then
            term.setBackgroundColor(colors.white)
            term.setTextColor(colors.black)
        else
            term.setBackgroundColor(colors.black)
            term.setTextColor(colors.white)
        end
        if bits[i*2] == true then
            term.write(grey)
        else
            term.write(" ")
        end
    end
    term.setBackgroundColor(colors.black)
    term.setTextColor(colors.white)
end


function PrintCsImage(hexes,max_y) -- Colour-dithered image, for lack of better term. Allows us to get more complex "colour combinations" by having... nevermind.
    term.clear()
    local length = math.ceil(#hexes/2)
    for i=1,length do
        local pos_y,pos_x = GetCoords(i,max_y)
        term.setCursorPos(pos_x,pos_y)
        term.setBackgroundColor(math.pow(2,hexes[(i*2)-1]))
        term.setTextColor(math.pow(2,hexes[i*2]))
        term.write(grey)
    end
    term.setBackgroundColor(colors.black)
    term.setTextColor(colors.white)
end

function OpenImage(path) -- This will not display it yet, just load its bytes into the memory and buffer it. Keep that in mind.
    local h = fs.open(path, "rb")
    if h == nil then
        h.close()
        return nil
    end
    local buf = { }
    buf.bytes = { }
    local c = h.read() -- We find out what mode the thing is.
    if c == nil or c < 128 then
        return nil
    else buf.mode = (c - 128)
    end
    buf.width = h.read()
    buf.height = h.read()
    local i = 1
    while true do
        c = h.read()
        if c == nil then
            h.close()
            break
        else
            buf.bytes[i] = c
        end
    end
    return buf
end

function DisplayImage(buf)
    if buf == nil then
        return nil
    end
    local pixel_buffer = { }
    local coloured = (buf.mode % 2 == 1)
    local dithered = (buf.mode >= 2)
    local pixels = { }
    if coloured == true then
        for key,value in ipairs(buf.bytes) do
            pixels[(key*2)-1],pixels[key*2] = splitHex(value)
        end
    else
        byte2bit(buf.bytes,pixels)
    end
    if dithered == true then
        if coloured == true then
            PrintCsImage(pixels,buf.width)
            return true
        else
            PrintGrImage(pixels,buf.width)
            return true
        end
    else
        if coloured == true then
            PrintCdImage(pixels,buf.width)
            return true
        else
            PrintBwImage(pixels,buf.width)
            return true
        end
    end
end