I'm in the same boat...

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.

I understand the arrows are done automatically for the main two research trees, but for some reason they do not work if you change the Fleet tree to make way for additional techs.  Here is a picture to show what I mean.  What I did in this demostration was copy the techs over from the combat tree of the TEC into my custom fleet tree without messing with any of the other attributes.

As you can see there are no arrows.  If I copy the fleet techs into the other two trees, the arrows show up, so I am just wondering how to get the fleet tree to reconize arrows.  So you see if I understood exactally how the other trees reconized the arrows in the first place I should be able to write the code for the Fleet Tree to reconize them as well. In theory that is

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.

Ugh, I was afraid of that but had my fingers crossed.  Anyway, I guess I'll change how I approch the Fleet screen. Maybe fill it with one shot researches or use the idea of "you must research the previous tech to access the next" approch.  Should not be too hard with the second approch, as most weapon and shield upgrades follow that already.  Anyway, thanks for the heads up Vandenburg. 

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

Yea, and it might have to come to that.  Just so much nicer having the arrows there and changing as you work on the mod so it is easier to know what goes where right off hand instead of having to have a finished product before making the arrows.  Guess I will have to pin and paper it for reference until then.

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.

This is why the only way to do it is to draw it in the background, unfortunately. Yes, there are various files that set up the arrows, but it's the engine code that places them between dependancies, that's why it's done automatically for the civilian/combat trees. There's no code in the engine to put them on the fleet 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...