Particle nodes

2D and 3D

Particles can be either 2D or 3D:

struct Particle2D {
    vec2  position;
    vec2  velocity;
    vec2  acceleration;
    float size;
    float lifetime;
    float lifetime_max;
    vec4  color;
    uint  index;
    bool  needs_init;
};

struct Particle3D {
    vec3  position;
    vec3  velocity;
    vec3  acceleration;
    float size;
    float lifetime;
    float lifetime_max;
    vec4  color;
    uint  index;
    bool  needs_init;
};

You will notice that the two are very similar, and the effects will be too. This is why you might want to write the effects only once, and have them apply to both 2D and 3D particles.

To do so, simply go to the Nodes/Particle Nodes Generator folder and add a .clbtemp file in the appropriate folder (Initializer, Force, etc.). Then run the particle_nodes_generator.py script to generate your 2D and 3D files.

Gravity.clbtemp

INPUT float 'Strength';
INPUT $Direction 'Direction';

$Particle main($Particle Particle)
{
    $vec force = 'Direction' * 'Strength';
    Particle.acceleration += force;
    return Particle;
}

.clbtemp files are exactly the same as .clbnode files, except that you have access to some dollar variables that will be replaced by either their 2D or 3D version. For example $vec will become vec2 for 2D particles and vec3 for 3D particles.

Here is the list of all of them:

Template	2D	3D
$vec	vec2	vec3
$vec34	vec3	vec4
$UV	UV	vec3
$Point	Point2D	vec3
$Direction	Direction2D	vec3
$Particle	Particle2D	Particle3D

Also, $vec is quite smart, so if you write for example $vec(a, b) it will become vec2(a, b) in 2D and vec3(a, b, 0.) in 3D.

You can also write code that will only appear in the 2D or 3D version, just like with an #ifdef block:

$$if(2D);
vec2 point = random_point_on_disk(random);
$$else;
vec3 point = random_point_on_sphere(random);
$$endif;

Finally, $gradient(p, 'Shape') will compute the gradient of an SDF. You can use it like this:

Attractor.clbtemp

INPUT $UV->SignedDistance 'Shape';
INPUT float 'Force';

$Particle main($Particle Particle)
{
    Particle.acceleration += 'Force' * $gradient(Particle.position, 'Shape');
    return Particle;
}

Under the hood it will generate a function like this:

vec2 gradient(vec2 p)
{
    float h = 0.001;
    return vec2(
               'Shape'(p - vec2(h, 0)) - 'Shape'(p + vec2(h, 0)),
               'Shape'(p - vec2(0, h)) - 'Shape'(p + vec2(0, h))
           )
           / (2. * h);
}

and call it with the first parameter p.

Forces

Forces will typically want to add something to the acceleration:

Gravity.clbtemp

INPUT float 'Strength';
INPUT $Direction 'Direction';

$Particle main($Particle Particle)
{
    $vec force = 'Direction' * 'Strength';
    Particle.acceleration += force;
    return Particle;
}

Initializers

Initializers are responsible for setting one of the attributes of the particle during the first frame of its lifetime. They need to check Particle.needs_init to only initialize when necessary:

Init Size.clbtemp

INPUT float 'Size';

$Particle main($Particle Particle)
{
    if (!Particle.needs_init)
        return Particle;

    Particle.size = 'Size';
    return Particle;
}