Bitmap/Bresenham's line algorithm

Using the data storage type defined on this page for raster graphics images, draw a line given 2 points with the Bresenham's algorithm (definition on Wikipedia).

OCaml

<ocaml>let draw_line ~img ~color ~p0:(x0,y0) ~p1:(x1,y1) =

 let steep = abs(y1 - y0) > abs(x1 - x0) in

 let plot =
   if steep
   then (fun x y -> put_pixel img color y x)
   else (fun x y -> put_pixel img color x y)
 in

 let x0, y0, x1, y1 =
   if steep
   then y0, x0, y1, x1
   else x0, y0, x1, y1
 in
 let x0, x1, y0, y1 =
   if x0 > x1
   then x1, x0, y1, y0
   else x0, x1, y0, y1
 in

 let delta_x = x1 - x0
 and delta_y = abs(y1 - y0) in
 let error = -delta_x / 2
 and y_step =
   if y0 < y1 then 1 else -1
 in
 let rec loop x y error =
   plot x y;
   if x <= x1 then
     let error = error + delta_y in
     let y, error =
       if error > 0
       then (y + y_step), (error - delta_x)
       else y, error
     in
     loop (succ x) y error
 in
 loop x0 y0 error

</ocaml>