Using the data storage type defined on this page for raster images, write the image to a PPM file (binary P6 prefered).

(Read the definition of PPM file on Wikipedia.)




 
 
-- helper function, simulates PHP's array_fill function
local array_fill = function(vbegin, vend, value)
    local t = {}
    for i=vbegin, vend do
        t[i] = value
    end
    return t
end
 
Bitmap = {}
Bitmap.__index = Bitmap
 
function Bitmap.new(width, height)
    local self = {}
    setmetatable(self, Bitmap)
    local white = array_fill(0, width, {255, 255, 255})
    self.data = array_fill(0, height, white)
    self.width = width
    self.height = height
    return self
end
 
function Bitmap:writeRawPixel(file, c)
    local dt
    dt = string.format("%c", c)
    file:write(dt)
end
 
function Bitmap:writeComment(fh, ...)
    local strings = {...}
    local str = ""
    local result
    for _, s in pairs(strings) do
        str = str .. tostring(s)
    end
    result = string.format("# %s\n", str)
    fh:write(result)
end
 
function Bitmap:writeP6(filename)
    local fh = io.open(filename, 'w')
    if not fh then
        error(string.format("failed to open %q for writing", filename))
    else
        fh:write(string.format("P6 %d %d 255\n", self.width, self.height))
        self:writeComment(fh, "automatically generated at ", os.date())
        for _, row in pairs(self.data) do
            for _, pixel in pairs(row) do
                self:writeRawPixel(fh, pixel[1])
                self:writeRawPixel(fh, pixel[2])
                self:writeRawPixel(fh, pixel[3])
            end
        end
    end
end
 
function Bitmap:fill(x, y, width, height, color)
    width = (width == nil) and self.width or width
    height = (height == nil) and self.height or height
    width = width + x
    height = height + y
    for i=y, height do
        for j=x, width do
            self:setPixel(j, i, color)
        end
    end
end
 
function Bitmap:setPixel(x, y, color)
    if x >= self.width then
        --error("x is bigger than self.width!")
        return false
    elseif x < 0 then
        --error("x is smaller than 0!")
        return false
    elseif y >= self.height then
        --error("y is bigger than self.height!")
        return false
    elseif y < 0 then
        --error("y is smaller than 0!")
        return false
    end
    self.data[y][x] = color
    return true
end
 
function example_colorful_stripes()
    local w = 260*2
    local h = 260*2
    local b = Bitmap.new(w, h)
    --b:fill(2, 2, 18, 18, {240,240,240})
    b:setPixel(0, 15, {255,68,0})
    for i=1, w do
        for j=1, h do
            b:setPixel(i, j, {
                    (i + j * 8) % 256,
                    (j + (255 * i)) % 256,
                    (i * j) % 256
                }
            );
        end
    end
    return b
end
 
example_colorful_stripes():writeP6('p6.ppm')
 