https://github.com/akkartik/mu/blob/main/503manhattan-line.mu

     1 fn draw-box-on-real-screen x1: int, y1: int, x2: int, y2: int, color: int {
     2   draw-horizontal-line-on-real-screen x1, x2, y1, color
     3   draw-vertical-line-on-real-screen x1, y1, y2, color
     4   draw-horizontal-line-on-real-screen x1, x2, y2, color
     5   draw-vertical-line-on-real-screen x2, y1, y2, color
     6 }
     7
     8 fn draw-horizontal-line-on-real-screen x1: int, x2: int, y: int, color: int {
     9   var x/eax: int <- copy x1
    10   {
    11     compare x, x2
    12     break-if->=
    13     pixel-on-real-screen x, y, color
    14     x <- increment
    15     loop
    16   }
    17 }
    18
    19 fn draw-vertical-line-on-real-screen x: int, y1: int, y2: int, color: int {
    20   var y/eax: int <- copy y1
    21   {
    22     compare y, y2
    23     break-if->=
    24     pixel-on-real-screen x, y, color
    25     y <- increment
    26     loop
    27   }
    28 }