Heretic-like screen wipe?

For the past few hours, I have been trying to figure out a way to make my mod not have a screen wipe. And I've really had no luck, but I found out that Heretic doesn't have a screen wipe. So does anyone know how to code a screen wipe like Heretic's?

You could start by reading the wiki. The screen wipe style is left at the user's preference, except for custom intermissions.

If your mod is a standalone TC, you can change the default wipe style by using the DEFCVARS lump to change the default value of wipetype.