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Upgrading to AGS 2.7

The script language in AGS 2.7 has changed quite significantly from previous versions. Many of the script commands have become object-based, which has several advantages over the previous approach. This page will attempt to introduce you to the new method and explain its benefits.

Firstly, so that you can get an idea of the changes, here's an example of some old-style script commands and their new equivalents:

AnimateObjectEx(0,2,0,0,0,1);
ListBoxAdd(3, 5, "New item");
becomes:
oWaterfall.Animate(2, 0, eOnce, eForwards, eBlock);
lstTest.AddItem("New item");
Just from looking at that example the advantages should be obvious; the script is more intuitive for people to learn, much easier to read (no guessing what all the numbers mean in the AnimateObjectEx call), and therefore you're less likely to make mistakes when using it. GUI controls having names brings it much more into line with Visual Basic-style GUI development, so you don't have to remember what control number all your buttons are.

The script editor's autocomplete functionality has been significantly enhanced to aid in all this as well. You'll see as you start to experiment that autocomplete pops up more often and lists only the relevant commands thanks to object-based scripting.

So does this mean I have to throw out all my scripts?

No, certainly not! The new version is fully backwards compatible, so all your existing scripts will continue to work just fine. However, for any new scripts that you write, it's strongly recommended that you use the new object-based commands.

Ok, so uh... what's changed exactly?

The script language syntax hasn't changed at all (that's the way you use semicolons, brackets, and so on). It's still just like it was before, but with some new additions. Most significantly, most commands are now called on something. For example, the old command:

StopMoving(EGO);

Just from looking at that, it's not at all obvious what StopMoving does. Does it stop a character moving, an object moving, or does it stop the screen moving? It's not intuitive. So now, rather than supplying the character as a parameter to the function, you actually call the function on the character. So:

character[EGO].StopMoving();

Now it's perfectly clear that it's the character EGO that we want to stop moving.

Suppose you're wondering what commands you can call on a character. Previously it was hard to tell, but now if you type character[EGO]. in the script editor, auto-complete will pop up and list all the valid functions and properties that you can access on the character.

So I have to keep typing character[EGO] all the time? What a pain!

Not so fast! Most of the new object-based commands can be called in two ways -- either through the main array as we just saw, but also through what's called the character's Script O-Name. This is a shorthand that allows you to directly access things, and for characters it is the script name in sentence case, with a "c" added to the beginning. So, in this example it would be:

cEgo.StopMoving();

This line has an identical effect to the one with character[EGO] that we used above.

Furthermore, the player variable is now kept up to date with the current player character, so it is actually useful. In a multi-character game, what you previously had to write like this:

StopMoving(GetPlayerCharacter());

can now be done like this:

player.StopMoving();

Hmm, I see... so what exactly has been object-ised?

Currently, the following object-based things are available:

Global array O-Name example
character[] cEgo
object[] oDoor
hotspot[] hTree
gui[] gInventory
inventory[] iPinkPoster
region[] (none)

GUI controls are handled slightly differently. They all have a script name, and are directly accessed via that. For example, if you set the script name of a list box to "lstSaves", then you would use "lstSaves." to access it. There is no global array of GUI controls.

How do I find out the new equivalents of old functions?

The help file's index has been set up to automatically redirect you to the new commands. Just open the help file, go to the index and type in the name of an old command, and it will bring you to the new object-based equivalent (if there is one).

Which commands haven't been changed?

Commands which don't operate on anything in particular (and therefore wouldn't really benefit from being object-based) have been left alone. For example, SaveGameSlot, QuitGame and so on have all remained identical to how they were in previous versions.

What's the deal with these "eBlock" type things?

AGS now supports enumerated types. Basically, in situations where you have to choose one from a list of possible options, an enumerated type (or enum) now steps in. In the past, you had commands with descriptions like this:

"Pass 1 if you want the function to block, or 0 if you don't".

This lead to lots of 1's and 0's in function calls, which are hard to read. Now, instead of this each number is represented by an easy-to-remember word (such as eBlock and eNoBlock). Even better, when you call a function that uses an enum parameter, auto-complete automatically pops up the list of options for you to choose from.

See the enum keyword description for information on how to create your own.

So do I have to pass all these things like eBlock every time I call the function?

Nope! Many functions now support optional parameters, where the most common options are selected automatically. If you look at the help for a function such as the Animate character command, you'll see some of the parameters are defined as "optional". This means that you don't have to supply them; if you don't, the default option that will be chosen is described in the help for that command.

So what else is new?

Well, 2.7 introduces the float data type, so AGS now finally supports floating-point arithmetic in your scripts. Also, for more advanced scripters, you can create your own member functions (including protected and static ones) to write cleaner script than just having a bunch of global functions.

Also, the script editor is now much better at checking your script for errors. You may well find that a script which compiled fine before no longer works on 2.7. Hopefully the error message should direct you towards fixing any problems.

Is there anything else I should watch out for?

Because of the new additions, the script language has more reserved words than before. For example, words like "gui", "object" and "hotspot" are now reserved (since they are used to access the global arrays). If your script uses any variables with these names, it will no longer work. You'll need to change the variable name in order to compile.

Also, the script language now supports pointers. Because they are a fairly complex topic, there's a separate page devoted to explaining what they are.

Blimey, that's a lot to take in. Where do I start?

I'd recommend attempting to write your next section of script in the new way. Each time you're about to use an old-style command, simply look it up in the manual to find out what it's replacement is.

Once you get used to the new system, I'm sure you'll agree that it is a significant improvement over the old scripting system and you'll start to enjoy the benefits of faster and more intuitive coding.

As always, if there's something you really can't get your head round, post on the AGS Forums and we'll help you out as best we can!

Have fun,
CJ

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