Tutorial - Basic Scripting

As scripting seems to be something difficult for most people to even start utilizing i thought it might be a good idea to write a short tutorial about the issue. Basic understanding of Lua or practically any other scripting or coding language is helpful but is not actually required as there is an abundance of well written guides to scripting in the internet. Some of these have been gathered to the links section in the Scripting.tbl page. Especially the Tutorial Directory in Lua-Users wiki is very usefull in learning to use Lua scripting with FreeSpace Open.

Simple mission with single fighter placed alone to the game. Intended for testing the use of scripts in FreeSpace Open, Scriptingtest.rar

Please post any comments or questions concerning the basic scripting tutorial to the talk page

Very Basics

First take a good look at the Scripting.tbl page. From there you can see the hooks you can use for scripting. In addition to these there are few additional in Weapons.tbl, namely $Collide Ship: and $Collide Weapon: but these arent supported by the 3.6.9 code branch.

All the hooks require square brackets after them into where the actual script is inserted.

Scripting.tbl

$Simulation:

[
...
]

First Example

Lets start with creating a small script that writes text to the screen. That is the very old Hello, World example. To achieve that effect we first need to create a scripting.tbl file and then also to create the needed sections. In order to achieve that goal first create a plain text document using (for example) notepad or similar non-autoformatting text editor.

• Name the empty text file as scripting.tbl
• Move it to data/tables directory
• Add the needed #Global Hooks and #End to the table.

Scripting.tbl

#Global Hooks

#End

Draw Text to Screen

To write text (or rather a text string) to the screen we need to use certain Lua functions. The needed function drawString() is located in the Graphics library (abbreviated gr), Graphic library in Scripting.html. To use that function we first need to create a $HUD: hook where we can place it. The function also needs some arguments and we ought to give it the required arguments. First we need the string 'Hello, World' followed by the location coordinates (pixels) where the game is instructed to draw the string. Also note that as the function is from the Graphics library we need to add gr. before the function (that is to write gr.drawString instead of just drawString).

Notice that we can comment (the rest of) the line away with double dashes, like so – –. This is usefull for adding notes to the scripts for later reference or for preventing certain lines of the script to be read.

Scripting.tbl

#Global Hooks

$HUD:

[

--Draws 'Hello, World' to the HUD
gr.drawString('Hello, World', 100, 100)

]

#End

Drawing in Different Locations

In the first example we draw the string so that it started from the position 100, 100. Now lets draw the same string also elsewhere on the screen.

Scripting.tbl

#Global Hooks

$HUD:

[

gr.drawString('Hello, World', 100, 100)
gr.drawString('Hello, World', 130, 160)
gr.drawString('Hello, World', 160, 220)
gr.drawString('Hello, World', 190, 280)

]

#End

Drawing in Different Colors

Now that we have several text strings drawn to the screen we might want to try to alter their colors. For this we need another function from the Graphics library, setColor() that accepts four arguments. These are basic RGBA values of which the A (alpha or transparency) is optional.

Scripting.tbl

#Global Hooks

$HUD:

[

gr.setColor(0, 255, 0)
gr.drawString('Hello, World', 100, 100)
gr.setColor(255, 0, 0)
gr.drawString('Hello, World', 130, 160)
gr.setColor(0, 0, 255)
gr.drawString('Hello, World', 160, 220)
gr.setColor(255, 255, 255, 128)
gr.drawString('Hello, World', 190, 280)

]

#End

NOTE: Some of the functions (mainly from graphics library) are specific to certain global hooks. That is if you try to use them in a wrong hook the script wont do anything. Game doesnt actually warn about this so you may have to figure this one out on simple trial-and-error method.

Drawing Particles

Next we will try drawing particles to the screen. Again we need the scripting.tbl for this

Scripting.tbl

#Global Hooks

#End

Scripted Particles

To draw (or render) particles to the screen we need to use other Lua functions than what we used in the text example. The required function is createParticle() from Testing library (abbreviated ts.) and to place it into the $Simulation: hook. This function requires several arguments but for this example we only need to use few of them. As can be seen from the scripting.html the function uses vector objects for the first two arguments followed by two numerical ones and several others.

This means however that before we can actually start using the function we need to get some vector objects. Function to create these objects can be found from Math (abbreviated ma.) library (newVector()). We also need to assign a type for the particle, for this purpose the 'Debug' is good enough. Other values can be set to be what ever we wish them to be. Its good to remember though that the script is executed every frame.

Scripting.tbl

#Global Hooks

$Simulation:

[

--1st create a new vector object and assign it as variable
nullvec = ma.newVector(0,0,0)

--2nd draw the particle
ts.createParticle(nullvec,nullvec,0.25,20,'Debug')

]

#End

Attaching Bitmaps to Particles

Now that we have managed to draw a particle to the screen we might want to start modifying it. Lets begin with changing the 'Debug' particle into something else. Lets select for example laserglow03 for this example. For this we first need to load the graphics into a texture handle, and that can be done with loadTexture function from the Graphics library. Then we must change the particle script a bit by adding several new (optional) arguments to it. This is done by first changing the earlier 'Debug' into 'Bitmap' followed by , -1, false and finally by the texture.

Scripting.tbl

#Global Hooks

$Simulation:

[

nullvec = ma.newVector(0,0,0)

--load a new graphic
particletexture = gr.loadTexture('laserglow03')

ts.createParticle(nullvec,nullvec,0.25,20,'Bitmap', -1, false, particletexture)

]

#End

Animations and Moving Particles

We can load animations as particle graphics and use these for creating new effects. This is done simply by adding to gr.loadTexture() function a new argument. We can also try moving both the particle effect and the changing the velocity of the spawned particle effect. Procedure is very similar to static and centered effect but this time we need create new vector objects for the particle velocity and the particle position.

Scripting.tbl

#Global Hooks

$Simulation:

[

--Create the new vectors
movevec = ma.newVector(0,20,0)
velvec = ma.newVector(20,0,1000)

--Load animation, true is needed for loading the animation
particletexture = gr.loadTexture('exp04',true)

ts.createParticle(movevec,velvec,1,20,'Bitmap', -1, false, particletexture)

]

#End

Using Statements

Now that we can handle basics of creating graphics on the screen we can move on to actually controlling them. For this it usefull first to read both Control Structure and For Tutorials from Lua-Users wiki.

Drawing Ship List on Screen

In first example we draw a list of ship using data read from the game with scripts. To do this we need access every ships status on every frame and therefore we will use for - do statement. We will need to place the script to $HUD: hook as we want to draw the results on HUD screen. Then we will need to define the limits of the for - do - end statement, this we can do using a function getNumShips() from Mission library (abbreviated mn.). Now we can access all ships simply by using getShipByIndex() function. As we do this we need to access several variables from ship object data (scripting.html).

Scripting.tbl

#Global Hooks

$HUD:

[

--For statement and its limits
for i=1,mn.getNumShips() do

   --we need to use the same letter (i) as in for statement
   --then we place the ship object to variable named 'ship'.
   ship = mn.getShipByIndex(i)
   
   --we wanted to draw the ships names to we need to access that data 
   shipname = ship.Name 

   --lets draw shipname string
   --to avoid drawing the names on top of each other 
   --add a calculation (80 + 20*i) to the arguments
   gr.drawString(shipname,100,80+20*i)

--for statement has to end
end

]

#End

NOTE: String may seem to be invisible but this can be easily fixed with the certain scripting functions that we tried earlier

Adding More to the List

Other data can also be drawn in similar way. Lets take for example the remaining hitpoints of the ship and the class of the ship.

Scripting.tbl

#Global Hooks

$HUD:

[

for i=1,mn.getNumShips() do

   ship = mn.getShipByIndex(i)
   shipname = ship.Name 

   --Get ship hitpoints
   shiphp = ship.HitpointsLeft

   --Get ship class
   shipclass = ship.Class.Name

   gr.drawString(shipname,100,80+20*i)
   gr.drawString(shiphp,200,80+20*i)
   gr.drawString(shipclass,300,80+20*i)

end

]

#End

Using If Statement

We can still add to the script for example a rudimentary IFF selective color coding. For this effect we need to use if - then - end statement.

Scripting.tbl

#Global Hooks

$HUD:

[

for i=1,mn.getNumShips() do

   ship = mn.getShipByIndex(i)
   shipname = ship.Name 
   shiphp = ship.HitpointsLeft
   shipclass = ship.Class.Name

   --we need to access ship species data
   shipteam = ship.Team.Name

   --here we start the if statement
   if shipteam == "Friendly" then
      gr.setColor(0,255,0)
   elseif shipteam == "Hostile" then
      gr.setColor(255,0,0)
   else 
      gr.setColor (0,255,255)
   end

   gr.drawString(shipname,100,80+20*i)
   gr.drawString(shiphp,200,80+20*i)
   gr.drawString(shipclass,300,80+20*i)

end

]

#End