-- Export canvas on love2d
-- Reference
-- https://love2d.org/forums/viewtopic.php?t=78901&start=10

function love.load()
  love.graphics.setDefaultFilter("nearest", "nearest")
  canvas = love.graphics.newCanvas(320, 240)
  font = love.graphics.newFont(16)

  req_export = false
  now_time_str = ""
end

function love.update(dt)
  now_time_str = os.date("%Y-%m-%d_%H-%M-%S")
end

function love.draw()
  -- set canvas
  love.graphics.setCanvas(canvas)

  -- clear canvas
  love.graphics.clear(0, 0, 0, 0)

  -- draw text
  love.graphics.setFont(font)

  love.graphics.setColor(0, 1, 0, 1)
  love.graphics.print("FPS: " .. tostring(love.timer.getFPS()), 2, 2)

  love.graphics.setColor(0, 1, 1, 1)
  love.graphics.print("SPACE key : Export canvas as png", 2, 20)

  love.graphics.setColor(1, 1, 0, 1)
  love.graphics.print(now_time_str, 2, 40)

  -- unset canvas
  love.graphics.setCanvas()

  -- draw canvas to screen
  love.graphics.setColor(1, 1, 1, 1)
  love.graphics.draw(canvas)

  if req_export then
    req_export = false

    -- export canvas as png
    local imagedata = canvas:newImageData()
    local filedata = imagedata:encode("png")
    local filename = now_time_str .. ".png"

    -- write file
    local filepng = io.open(filename, "wb")
    if filepng ~= nil then
      filepng:write(filedata:getString())
      filepng:close()
    end

    local ty = love.graphics.getHeight() - 40
    love.graphics.print("Export !", 2, ty)
  end
end

function love.keypressed(key, isrepeat)
  if key == "escape" then
    -- ESC key to exit
    love.event.quit()
  elseif key == "space" then
    -- SPACE key to export canvas
    req_export = true
  end
end