|--| Are we at the end of a line?
| end of line?,x|x,~ end of line| end of line?| end of line

|--| Are we at the end of the screen?
| end of screen?,y|y,~ end of screen| end of screen?| end of screen

|--| Co pixel_y the pixel coordinates from `x/y` to `@pixel-x/@pixel-y`.
| pixel_x=x,x|*x,@pixel-x, pixel_x=x
| pixel_x=x|
| pixel_y=y,y|*y,@pixel-y, pixel_y=y
| pixel_y=y|

|--| Compute some pixel colors based on the `x/y` coordinates.
|--| r = x, g = y, b = x + y
| pixel_red=x,x|*x,@pixel-r, pixel_red=x| pixel_red=x|
| pixel_green=y,y|*y,@pixel-g, pixel_green=y| pixel_green=y|
| pixel_blue=x+y,x|*x,@pixel-b, pixel_blue=x+y
| pixel_blue=x+y,y|*y,@pixel-b, pixel_blue=x+y
| pixel_blue=x+y|

|--| Copy temporaries back to their respective variables.
|*x|x|*y|y

|plot_pixel| pixel_x, pixel_y, pixel_red, pixel_green, pixel_blue,ps
| pixel_x| pixel_x=x:399
| pixel_y| pixel_y=y:399
| pixel_red| pixel_red=x:399
| pixel_green| pixel_green=y:399
| pixel_blue| pixel_blue=x+y:399
|ps|@set-pixel

|--| Move the `x/y` coordinates.
|x-,x||x-||y-,y||y-|

|--| Main loop.
||x:399,y:399
|draw, end of line,x|draw, end of line,draw
|draw, end of line|draw, end of screen?, @display
|draw,~ end of line|plot_pixel,x-,draw
|draw, end of screen|plot_pixel,x:399,y:399
|draw,~ end of screen,x|draw,~ end of screen
|draw,~ end of screen|y-,x:399,draw
|draw| end of line?,draw

|--| clean up remaining facts
|x||y|

||draw