Particle shaders

Particle shaders are a special type of vertex 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 the CanvasItem of Spatial shader. They contain only a vertex processor function that outputs multiple properties (see built-ins below).

Particle shaders use a transform feedback shader, which is a special type of vertex shader that runs on its own. It takes in data in a buffer like a regular vertex shader does, but it also outputs to data buffers instead of outputting to the fragment shader for pixel-processing. Because of this, transform feedback shaders can build on themselves each run, unlike other shaders that discard the data they have calculated once they draw to the frame buffer.

Note

Particle shaders are only available in the GLES3 backend. If you need particles in GLES2, use CPUParticles.

Render modes

Render mode

Description

keep_data

Do not clear previous data on restart.

disable_force

Disable attractor force.

disable_velocity

Ignore VELOCITY value.

Built-ins

Values marked as "in" are read-only. Values marked as "out" are for optional writing and will not necessarily contain sensible values. Values marked as "inout" provide a sensible default value, and can optionally be written to. Samplers are not subjects of writing and they are not marked.

Global built-ins

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

Built-in

Description

in float TIME

Global time, in seconds.

in float PI

A PI constant (3.141592). A ration of 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

A E constant (2.718281). Euler's number and a base of the natural logarithm.

Start and Process built-ins

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 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.

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

in bool RESTART_ROT_SCALE

in bool RESTART_VELOCITY

in bool RESTART_COLOR

in bool RESTART_CUSTOM

in bool RESTART_VELOCITY

Process built-ins

Built-in

Description

in bool RESTART

true if the current process frame is first for the particle.

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 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 vec3(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

Function

Description

bool emit_subparticle (mat4 xform, vec3 velocity, vec4 color, vec4 custom, uint flags)

Forces to emit a particle from a sub-emitter.