Dynamic Inputs - GiantLuigi4/Minecraft_Effekseer_Implementation GitHub Wiki
For a lot of things, you will probably need more control over your effeks.
To do this, you need an Dynamic Input and an expression.

Here's a simple expression to rotate the effek based off dynamic inputs.
@O.x = @In0
@O.y = @In1
@O.z = @In2

Here's where you can find the above effek
In the effek above, Controller has its rotation set to "ParamaterType Fixed", and the "Ex." or "Expression" set to the Rotation expression

Mover just moves on a linear path at a speed of 1 on the z axis
Effek effek = Effeks.get("test:bullet");
if (effek != null) {
EffekEmitter emitter = effek.getOrCreate("test:test");
emitter.setPosition(
Minecraft.getInstance().player.getPosX(),
Minecraft.getInstance().player.getPosY(),
Minecraft.getInstance().player.getPosZ()
);
emitter.setPaused(false);
emitter.setDynamicInput(0, (float)Math.toRadians(Minecraft.getInstance().player.rotationPitch));
emitter.setDynamicInput(1, (float)Math.toRadians(-Minecraft.getInstance().player.rotationYaw));
emitter.setDynamicInput(2, 0);
}
}
Here's some sample code to make the effek rotate based off the direction the player's looking