local canvas = require "canvas"

local function line(c, x0, y0, x1, y1, col)
    local dx = math.abs(x1 - x0)
    local dy = math.abs(y1 - y0)
    local sx = (x0 < x1) ? 1 : -1
    local sy = (y0 < y1) ? 1 : -1
    local err = (dx > dy ? dx : - dy) // 2
    while true do
        c:set(x0, y0, col)
        if x0 == x1 and y0 == y1 then break end
        local e2 = err
        if e2 > -dx then
            err -= dy
            x0 += sx
        end
        if e2 < dy then
            err += dx
            y0 += sy
        end
    end
end

local c = canvas.new(400, 400)
c:fill(0xffffff)                    -- white background
line(c, 0, 0, 399, 399, 0x0000ff)   -- draw a red diagonal
io.contents("mybmp.bmp", c:tobmp()) -- save to a bitmap file