let cmd_dvips tmpprefix = "dvips -q -R -E " ^ tmpprefix ^ ".dvi -f >" ^ tmpprefix ^ ".ps"
let cmd_latex tmpprefix = "latex " ^ tmpprefix ^ ".tex >/dev/null"
(* Putting -transparent white in converts arguments will sort-of give you transperancy *)
let cmd_convert tmpprefix finalpath = "convert -quality 100 -density 120 " ^ tmpprefix ^ ".ps " ^ finalpath ^ " >/dev/null 2>/dev/null"
(* Putting -bg Transparent in dvipng's arguments will give full-alpha transparency *)
(* Note that IE have problems with such PNGs and need an additional javascript snippet *)
(* Putting -bg transparent in dvipng's arguments will give binary transparency *)
let cmd_dvipng tmpprefix finalpath backcolor = "dvipng -bg \'" ^ backcolor ^ "\' -gamma 1.5 -D 120 -T tight --strict " ^ tmpprefix ^ ".dvi -o " ^ finalpath ^ " >/dev/null 2>/dev/null"

exception ExternalCommandFailure of string

let render tmppath finalpath outtex md5 backcolor =
    let tmpprefix0 = (string_of_int (Unix.getpid ()))^"_"^md5 in
    let tmpprefix = (tmppath^"/"^tmpprefix0) in
    let unlink_all () =
      begin
        (* Commenting this block out will aid in debugging *)
	Sys.remove (tmpprefix ^ ".dvi");
	Sys.remove (tmpprefix ^ ".aux");
	Sys.remove (tmpprefix ^ ".log");
        Sys.remove (tmpprefix ^ ".tex");
	if Sys.file_exists (tmpprefix ^ ".ps")
	then Sys.remove (tmpprefix ^ ".ps");
      end in
    let f = (Util.open_out_unless_exists (tmpprefix ^ ".tex")) in
      begin
	output_string f (Texutil.get_preface ());
	output_string f outtex;
	output_string f (Texutil.get_footer ());
	close_out f;
	if Util.run_in_other_directory tmppath (cmd_latex tmpprefix0) != 0
	then (unlink_all (); raise (ExternalCommandFailure "latex"))
	else if (Sys.command (cmd_dvipng tmpprefix (finalpath^"/"^md5^".png") backcolor) != 0)
	then (if (Sys.command (cmd_dvips tmpprefix) != 0)
	then (unlink_all (); raise (ExternalCommandFailure "dvips"))
	else if (Sys.command (cmd_convert tmpprefix (finalpath^"/"^md5^".png")) != 0)
	then (unlink_all (); raise (ExternalCommandFailure "convert"))
	else unlink_all ())
	else unlink_all ()
      end
