The arrows are done automatically, as long as the graphic exists for the kind of arrow it needs (they are in a .tga file somewhere in the Textures folder). There's an arrow that points one cell to the right, so if you have a tech at [0,0] and then create a new tech with that prereq and put it at [0,1], it will automatically draw the arrow.

Since the selection of arrows is somewhat limited (don't think there's 2 up/2 down, just 1 up/1 down for example) it won't be able to draw them for all conceivable dependancies, though.

AFAIK the fleet research screen doesn't use any code to create the arrows. IIRC it just uses its background screen for the look so it won't be possible to change that.

Well, you could cheat a bit.. if every race will end up using the same layout of the fleet tree, you *could* just modify the background image and draw in the arrows yourself

I don't think custom backgrounds is the answer. Especially given that almost everything else in the game is available to us in a file somewhere.

Some investigation has revealed the following:

The Graphics for the Arrows is contained in the file BackdropInGame.tga

The Individual Arrows are defined in the file Screen-InGame.brushes

The Individual Arrows are given a name, for want of a better description, in the file ResearchScreen.window

However I have not yet managed find where the Arrows are used to allow them to showup in the Research screen.

Thanks Annatar11, however I'm not interested in the Fleet screen, only the Civ/Mil screens.

You are correct in what you say about the arrows being placed automatically. I've found that if I move my Research items around so they are positioned within the bounds of an Arrow, then an Arrow will be displayed. However its not ideal for all my tree setup, so I'm going to see if I can add an additional arrow to the .tga file and associated files, that does fit my desired placement and see if its displayed...