From Spring

CEG Operators


The engine source code which implements the CEG operators is viewable here:


You are not limited to using fixed numbers in CEGs for positions, speeds, and so forth. Instead, you can use operators to change the CEG based on a variety of things.


Operators are read left to right. The operand is always to the right of the operator. Spaces are ignored, except to separate numbers. A number with no operator defaults to addition.

The Buffer

CEG provides you with a buffer in which you can store numbers using the yank ('y') operator. This buffer can store 16 values, numbered 0 to 15.


These are listed in the format "Operator Name (operator)".

Index ('i')

Multiplies the operand by the current count index. This index starts at 0 and increments every time the spawn is run, until the spawn has run a number of times equal to its count.

Suggested use: Spawning things in a line.

Rand ('r')

Multiplies the operand by a random float between 0 and 1.

Suggested use: Keeping explosions from looking too "perfect", making explosions look different every time.

Damage ('d')

Multiplies the operand by damage.

CEG_DAMAGE: In a COB script, you can do SET CEG_DAMAGE [value]. Any emit-sfx instructions will then use that value for the "damage" (use the 'd' operator to access this value).

Sawtooth ('m')

Calculates the floating-point remainder of the operand.

Discrete ('k')

Calculates the floor of the operand.

Sine ('s')

Calculates the sine of the operand.

Yank ('y')

Saves the running result into buffer[operand], and resets the running result to zero.

Multiply ('x')

Multiplies the running result by buffer[operand].

Add Buffer ('a')

Adds buffer[operand] to the running result.

Power ('p')

Raises the running result to the operandth power

Power Buffer ('q')

Raises the running result to the buffer[operand]th power.

Add (default)

Adds the operand to the running result. This operator is used if no other operator is given.


Using 'r'

This is an example of a script that makes 10 smoke particles:

Heavy_Laser_Expl = {
  smoke = {
    water = true,
    ground = true,
    count = 10,
    properties = {
      -- age increase per frame, when age >= 1  the particle is destroyed
      ageSpeed = 0.04,
      size = 40,
      sizeGrowth = -2,
      pos = [[-30 r60, r30, -30 r60]],
      speed = [[0.75 r-1.5, 1.7 r1.6, 0.75 r-1.5]],

For example in this snippet: pos = [[-30 r60, r30, -30 r60]]

The x coordinate (specified with -30 r60) will be: x = -30 + (Random value between 0 and 60)

Using 'i'

Here is an example that uses the index (i) command in the properties:

heatcloud = {
  ground = true,
  count = 10,
  properties = {
    pos = [[0, i20, 0]],
    heat = 10,
    maxheat = 10,
    heatFalloff = 1,
    size = 30,

This script creates a tower of heatcloud projectile. The first projectile gets y=0, the second y=20, y=40, y=60, .. and finally y=180.

Using 'x' and 'y'

i0.03125y0 -0.2x0x0

This multiplies the index by 0.03125 and saves it to buffer[0]. It then multiplies -0.2 by buffer[0] twice. The result is then -0.2 (i * 0.03125)^2. This type of thing is useful for making a series of particles follow a curved path.