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First steps with Scripting

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I am far from being an expert in the realm of scripting, but simple scripts are not too difficult to understand.
I will try to keep it very simple.

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Let's say you want to open a door in a particular fashion. The normal way would be to apply an action special 11: Open Door to:

1. a linedef with the player crosses trigger
   
   
   

   Example pwad

   
   
   
2. a switch with the use trigger
   
   
   

   Example pwad

   
   
   
3. a player enters/leaves a sector thing
   
   
   

   Example pwad

   
   
   
4. kill a monster
   
   
   

   Example pwad

   
   
   

In all of those cases the player causes a single event, namely to open a door.

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But how does one apply a script to do the same thing?
The structure of a script is thus:

#include "zcommon.acs"
script 1 (void)
{
// do some stuff
}

So, what does that mean? Let's take a look at each line.

#include "zcommon.acs" is very important. Without it the compiler will not know what to do.
Actually, zcommon.acs is a short version of including 3 separate definitions:

1. zwvars.acs - world-variable declarations (this is usually empty)
2. zdefs.acs - a list of all common zdoom definitions
3. zspecial.acs - a list of all action specials

From time to time, check out https://github.com/rheit/acc/ for the latest versions.

If one wanted to, one could write this also as:

#include "zwvars.acs"
#include "zdefs.acs"
#include "zspecial.acs"
script 1 (void)
{
// do some stuff
}

script 1 (void) tells the compiler the script is of type (void). There are other types. GZDoom now allows to specify a script by name instead of by a number. For example:

script"Open a Door" instead of script 1"

(void) is used when some event is triggered in the map.

Each body of the script must be within curly brackets:
{ at the start of the script
} at the end of the script

// can be used to type some comment to remind you what that line is about in case you come back to it later

Therefore, to use a script to open a door, as in the above examples, the script would look like this:

#include "zcommon.acs"
script 1 (void)
{
// 11: Door_Open (tag, speed, lighttag);
// Open a Door after the Demon is killed

	 Door_Open (100, 10, 0);

// 100 is tag of the door sector
// 10 is speed of the door opening up
// keep lighttag at 0
}

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Once you finish the script text, it must be compiled. Press the compile button. If an error creeps in, then the compiler will show a message at the bottom of the window.

Here it is in action when killing a monster:

Example pwad

Now, rather then attaching the action special 11: Open_Door as in the top examples, the action special
80: Script_Execute is attached. Do not forget to specify the script number.

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With ACS being a derivative of the C language, many possibilties open up.

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