Particle systems (2D)

Intro

A simple (but flexible enough for most uses) particle system is provided. Particle systems are used to simulate complex physical effects, such as sparks, fire, magic particles, smoke, mist, etc.

The idea is that a “particle” is emitted at a fixed interval and with a fixed lifetime. During its lifetime, every particle will have the same base behavior. What makes each particle different from the rest and provides a more organic look is the “randomness” associated with each parameter. In essence, creating a particle system means setting base physics parameters and then adding randomness to them.

Particle nodes

Godot provides two different nodes for 2D particles, Particles2D and CPUParticles2D. Particles2D is more advanced and uses the GPU to process particle effects, but that limits it to higher end graphics API, and in our case to the GLES3 renderer. For projects using the GLES2 backend, CPUParticles2D is a CPU-driven option with near feature parity with Particles2D, but lesser performance. While Particles2D is configured via a ParticlesMaterial (and optionally with a custom shader), the matching options are provided via node properties in CPUParticles2D (with the exception of the trail settings). You can convert a Particles2D node into a CPUParticles2D node by clicking on the node in the inspector, and selecting “Convert to CPUParticles2D” in the “Particles” menu of the toolbar.

../../_images/particles_convert.png

The rest of this tutorial is going to use the Particles2D node. First, add a Particles2D node to your scene. After creating that node you will notice that only a white dot was created, and that there is a warning icon next to your Particles2D node in the inspector. This is because the node needs a ParticlesMaterial to function.

ParticlesMaterial

To add a process material to your particles node, go to Process Material in your inspector panel. Click on the box next to Material, and from the dropdown menu select New ParticlesMaterial.

../../_images/particles_material.png

Your Particles2D node should now be emitting white points downward.

../../_images/particles1.png

Texture

A particle system uses a single texture (in the future this might be extended to animated textures via spritesheet). The texture is set via the relevant texture property:

../../_images/particles2.png

Time parameters

Lifetime

The time in seconds that every particle will stay alive. When lifetime ends, a new particle is created to replace it.

Lifetime: 0.5

../../_images/paranim14.gif

Lifetime: 4.0

../../_images/paranim15.gif

One Shot

When enabled, a Particles2D node will emit all of its particles once and then never again.

Preprocess

Particle systems begin with zero particles emitted, then start emitting. This can be an inconvenience when loading a scene and systems like a torch, mist, etc. begin emitting the moment you enter. Preprocess is used to let the system process a given number of seconds before it is actually drawn the first time.

Speed Scale

The speed scale has a default value of 1 and is used to adjust the speed of a particle system. Lowering the value will make the particles slower while increasing the value will make the particles much faster.

Explosiveness

If lifetime is 1 and there are 10 particles, it means a particle will be emitted every 0.1 seconds. The explosiveness parameter changes this, and forces particles to be emitted all together. Ranges are:

  • 0: Emit particles at regular intervals (default value).
  • 1: Emit all particles simultaneously.

Values in the middle are also allowed. This feature is useful for creating explosions or sudden bursts of particles:

../../_images/paranim18.gif

Randomness

All physics parameters can be randomized. Random values range from 0 to 1. The formula to randomize a parameter is:

initial_value = param_value + param_value * randomness

Fixed FPS

This setting can be used to set the particle system to render at a fixed FPS. For instance, changing the value to 2 will make the particles render at 2 frames per second. Note this does not slow down the particle system itself.

Fract Delta

This can be used to turn Fract Delta on or off.

Drawing parameters

Visibility Rect

The visibility rectangle controls the visibility of the particles on screen. If this rectangle is outside of the viewport, the engine will not render the particles on screen.

The rectangle’s W and H properties respectively control its Width and its Height. The X and Y properties control the position of the upper-left corner of the rectangle, relative to the particle emitter.

You can have Godot generate a Visibility Rect automatically using the toolbar above the 2d view. To do so, select the Particles2D node and Click Particles > Generate Visibility Rect. Godot will simulate the Particles2D node emitting particles for a few seconds and set the rectangle to fit the surface the particles take.

You can control the emit duration with the Generation Time (sec) option. The maximum value is 25 seconds. If you need more time for your particles to move around, you can temporarily change the preprocess duration on the Particles2D node.

Local Coords

By default this option is on, and it means that the space that particles are emitted to is relative to the node. If the node is moved, all particles are moved with it:

../../_images/paranim20.gif

If disabled, particles will emit to global space, meaning that if the node is moved, already emitted particles are not affected:

../../_images/paranim21.gif

Draw Order

This controls the order in which individual particles are drawn. Index means particles are drawn according to their emission order (default). Lifetime means they are drawn in order of remaining lifetime.

ParticlesMaterial settings

Spread

This parameter is the angle in degrees which will be randomly added in either direction to the base Direction. A spread of 180 will emit in all directions (+/- 180). For spread to do anything the “Initial Velocity” parameter must be greater than 0.

../../_images/paranim3.gif

Gravity

The gravity applied to every particle.

../../_images/paranim7.gif

Initial Velocity

Initial velocity is the speed at which particles will be emitted (in pixels/sec). Speed might later be modified by gravity or other accelerations (as described further below).

../../_images/paranim4.gif

Angular Velocity

Angular velocity is the initial angular velocity applied to particles.

Spin Velocity

Spin velocity is the speed at which particles turn around their center (in degrees/sec).

../../_images/paranim5.gif

Orbit Velocity

Orbit velocity is used to make particles turn around their center.

../../_images/paranim6.gif

Linear Acceleration

The linear acceleration applied to each particle.

Radial Acceleration

If this acceleration is positive, particles are accelerated away from the center. If negative, they are absorbed towards it.

../../_images/paranim8.gif

Tangential Acceleration

This acceleration will use the tangent vector to the center. Combining with radial acceleration can do nice effects.

../../_images/paranim9.gif

Damping

Damping applies friction to the particles, forcing them to stop. It is especially useful for sparks or explosions, which usually begin with a high linear velocity and then stop as they fade.

../../_images/paranim10.gif

Angle

Determines the initial angle of the particle (in degrees). This parameter is mostly useful randomized.

../../_images/paranim11.gif

Scale

Determines the initial scale of the particles.

../../_images/paranim12.gif

Color

Used to change the color of the particles being emitted.

Hue variation

The Variation value sets the initial hue variation applied to each particle. The Variation Random value controls the hue variation randomness ratio.

Emission Shapes

ParticlesMaterials allow you to set an Emission Mask, which dictates the area and direction in which particles are emitted. These can be generated from textures in your project.

Ensure that a ParticlesMaterial is set, and the Particles2D node is selected. A “Particles” menu should appear in the Toolbar:

../../_images/emission_shapes1.png

Open it and select “Load Emission Mask”:

../../_images/emission_shapes2.png

Then select which texture you want to use as your mask:

../../_images/emission_shapes3.png

A dialog box with several settings will appear.

Emission Mask

Three types of emission masks can be generated from a texture:

  • Solid Pixels: Particles will spawn from any area of the texture, excluding transparent areas.
../../_images/emission_mask_solid.gif
  • Border Pixels: Particles will spawn from the outer edges of the texture.
../../_images/emission_mask_border.gif
  • Directed Border Pixels: Similar to Border Pixels, but adds extra information to the mask to give particles the ability to emit away from the borders. Note that an Initial Velocity will need to be set in order to utilize this.
../../_images/emission_mask_directed_border.gif

Emission Colors

Capture from Pixel will cause the particles to inherit the color of the mask at their spawn points.

Once you click “OK”, the mask will be generated and set to the ParticlesMaterial, under the Emission Shape section:

../../_images/emission_shapes4.png

All of the values within this section have been automatically generated by the “Load Emission Mask” menu, so they should generally be left alone.

Note

An image should not be added to Point Texture or Color Texture directly. The “Load Emission Mask” menu should always be used instead.