Attention: Here be dragons (unstable version)

This is the latest (unstable) version of this documentation, which may document features not available in or compatible with released stable versions of Redot.

Checking the stable version of the documentation...

Particle shaders

Particle shaders are a special type of shader that runs before the object is drawn. They are used for calculating material properties such as color, position, and rotation. They are drawn with any regular material for CanvasItem or Spatial, depending on whether they are 2D or 3D.

Particle shaders are unique because they are not used to draw the object itself; they are used to calculate particle properties, which are then used by a CanvasItem or Spatial shader. They contain two processor functions: start() and process().

Unlike other shader types, particle shaders keep the data that was output the previous frame. Therefore, particle shaders can be used for complex effects that take place over multiple frames.

Note

Particle shaders are only available with GPU-based particle nodes (GPUParticles2D and GPUParticles3D).

CPU-based particle nodes (CPUParticles2D and CPUParticles3D) are rendered on the GPU (which means they can use custom CanvasItem or Spatial shaders), but their motion is simulated on the CPU.

Render modes

Render mode	Description
keep_data	Do not clear previous data on restart.
disable_force	Disable attractor force.
disable_velocity	Ignore `VELOCITY` value.
collision_use_scale	Scale the particle's size for collisions.

Built-ins

Values marked as in are read-only. Values marked as out can optionally be written to and will not necessarily contain sensible values. Values marked as inout provide a sensible default value, and can optionally be written to. Samplers cannot be written to so they are not marked.

Global built-ins

Global built-ins are available everywhere, including custom functions.

Built-in	Description
in float TIME	Global time since the engine has started, in seconds. It repeats after every `3,600` seconds (which can be changed with the rollover setting). It's not affected by time_scale or pausing. If you need a `TIME` variable that can be scaled or paused, add your own global shader uniform and update it each frame.
in float PI	A `PI` constant (`3.141592`). A ratio of a circle's circumference to its diameter and amount of radians in half turn.
in float TAU	A `TAU` constant (`6.283185`). An equivalent of `PI * 2` and amount of radians in full turn.
in float E	An `E` constant (`2.718281`). Euler's number and a base of the natural logarithm.

Start and Process built-ins

These properties can be accessed from both the start() and process() functions.

Function	Description
in float LIFETIME	Particle lifetime.
in float DELTA	Delta process time.
in uint NUMBER	Unique number since emission start.
in uint INDEX	Particle index (from total particles).
in mat4 EMISSION_TRANSFORM	Emitter transform (used for non-local systems).
in uint RANDOM_SEED	Random seed used as base for random.
inout bool ACTIVE	`true` when the particle is active, can be set `false`.
inout vec4 COLOR	Particle color, can be written to and accessed in mesh's vertex function.
inout vec3 VELOCITY	Particle velocity, can be modified.
inout mat4 TRANSFORM	Particle transform.
inout vec4 CUSTOM	Custom particle data. Accessible from shader of mesh as `INSTANCE_CUSTOM`.
inout float MASS	Particle mass, intended to be used with attractors. Equals `1.0` by default.
in vec4 USERDATAX	Vector that enables the integration of supplementary user-defined data into the particle process shader. `USERDATAX` are six built-ins identified by number, `X` can be numbers between 1 and 6, for example `USERDATA3`.
in uint FLAG_EMIT_POSITION	A flag for using on the last argument of `emit_subparticle()` function to assign a position to a new particle's transform.
in uint FLAG_EMIT_ROT_SCALE	A flag for using on the last argument of `emit_subparticle()` function to assign the rotation and scale to a new particle's transform.
in uint FLAG_EMIT_VELOCITY	A flag for using on the last argument of `emit_subparticle()` function to assign a velocity to a new particle.
in uint FLAG_EMIT_COLOR	A flag for using on the last argument of `emit_subparticle()` function to assign a color to a new particle.
in uint FLAG_EMIT_CUSTOM	A flag for using on the last argument of `emit_subparticle()` function to assign a custom data vector to a new particle.
in vec3 EMITTER_VELOCITY	Velocity of the Particles2D (3D) node.
in float INTERPOLATE_TO_END	Value of interp_to_end (3D) property of Particles node.
in uint AMOUNT_RATIO	Value of amount_ratio (3D) property of Particles node.

Note

In order to use the COLOR variable in a StandardMaterial3D, set vertex_color_use_as_albedo to true. In a ShaderMaterial, access it with the COLOR variable.

Start built-ins

Built-in	Description
in bool RESTART_POSITION	`true` if particle is restarted, or emitted without a custom position (i.e. this particle was created by `emit_subparticle()` without the `FLAG_EMIT_POSITION` flag).
in bool RESTART_ROT_SCALE	`true` if particle is restarted, or emitted without a custom rotation or scale (i.e. this particle was created by `emit_subparticle()` without the `FLAG_EMIT_ROT_SCALE` flag).
in bool RESTART_VELOCITY	`true` if particle is restarted, or emitted without a custom velocity (i.e. this particle was created by `emit_subparticle()` without the `FLAG_EMIT_VELOCITY` flag).
in bool RESTART_COLOR	`true` if particle is restarted, or emitted without a custom color (i.e. this particle was created by `emit_subparticle()` without the `FLAG_EMIT_COLOR` flag).
in bool RESTART_CUSTOM	`true` if particle is restarted, or emitted without a custom property (i.e. this particle was created by `emit_subparticle()` without the `FLAG_EMIT_CUSTOM` flag).

Process built-ins

Built-in	Description
in bool RESTART	`true` if the current process frame is first for the particle.
in bool COLLIDED	`true` when the particle has collided with a particle collider.
in vec3 COLLISION_NORMAL	A normal of the last collision. If there is no collision detected it is equal to `(0.0, 0.0, 0.0)`.
in float COLLISION_DEPTH	A length of normal of the last collision. If there is no collision detected it is equal to `0.0`.
in vec3 ATTRACTOR_FORCE	A combined force of the attractors at the moment on that particle.

Process functions

emit_subparticle() is currently the only custom function supported by particles shaders. It allows users to add a new particle with specified parameters from a sub-emitter. The newly created particle will only use the properties that match the flags parameter. For example, the following code will emit a particle with a specified position, velocity, and color, but unspecified rotation, scale, and custom value:

mat4 custom_transform = mat4(1.0);
custom_transform[3].xyz = vec3(10.5, 0.0, 4.0);
emit_subparticle(custom_transform, vec3(1.0, 0.5, 1.0), vec4(1.0, 0.0, 0.0, 1.0), vec4(1.0), FLAG_EMIT_POSITION | FLAG_EMIT_VELOCITY | FLAG_EMIT_COLOR);

Function	Description
bool emit_subparticle (mat4 xform, vec3 velocity, vec4 color, vec4 custom, uint flags)	Emits a particle from a sub-emitter.