Pixels

• ((draw-pixel viewport) p color)
  draw-pixel takes a viewport descriptor. It returns a function that draws a pixel in viewport at the specified position. The optional color argument defaults to black.
• ((clear-pixel viewport) p)
  clear-pixel takes a viewport descriptor. It returns a function that clears a pixel in viewport at the specified position.
• ((flip-pixel viewport) p)
  flip-pixel takes a viewport descriptor. It returns a function that flips a pixel in viewport at the specified position.