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Sistemi di particelle 2D

Introduzione

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.

Nodi di particelle

Godot fornisce due diversi nodi per particelle 2D, GPUParticles2D e CPUParticles2D. GPUParticles2D è più avanzato e utilizza la GPU per elaborare gli effetti delle particelle. CPUParticles2D è un'opzione gestita dalla CPU con parità di funzionalità vicina a GPUParticles2D, ma con prestazioni inferiori con una grande quantità di particelle. D'altra parte, CPUParticles2D potrebbe funzionare meglio su sistemi di fascia bassa o in situazioni con colli di bottiglia dovuti alla GPU.

Mentre GPUParticles2D è configurato tramite un ParticleProcessMaterial (e facoltativamente con uno shader personalizzato), le opzioni corrispondenti sono fornite tramite le proprietà del nodo stesso in CPUParticles2D (ad eccezione delle impostazioni della scia).

Going forward there are no plans to add new features to CPUParticles2D, though pull requests to add features already in GPUParticles2D will be accepted. For that reason we recommend using GPUParticles2D unless you have an explicit reason not to.

Puoi convertire un nodo GPUParticles2D in un nodo CPUParticles2D cliccando sul nodo nell'albero di scene, selezionando lo spazio di lavoro 2D e selezionando CPUParticles2D > Converti in CPUParticles2D nella barra degli strumenti.

È anche possibile convertire un nodo GPUParticles2D in un nodo CPUParticles2D, ma potrebbero esserci problemi se utilizzi funzionalità esclusive per la GPU.

The rest of this tutorial is going to use the GPUParticles2D node. First, add a GPUParticles2D 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 GPUParticles2D node in the scene dock. This is because the node needs a ParticleProcessMaterial to function.

ParticleProcessMaterial

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 ParticleProcessMaterial.

Your GPUParticles2D node should now be emitting white points downward.

Texture

A particle system can use a single texture or an animation flipbook. A flipbook is a texture that contains several frames of animation that can be played back, or chosen at random during emission. This is equivalent to a spritesheet for particles.

The texture is set via the Texture property:

Utilizzo di un flipbook di animazione

Particle flipbooks are suited to reproduce complex effects such as smoke, fire, explosions. They can also be used to introduce random texture variation, by making every particle use a different texture. You can find existing particle flipbook images online, or pre-render them using external tools such as Blender or EmberGen.

Example of a particle system that uses a flipbook texture

Using an animation flipbook requires additional configuration compared to a single texture. For demonstration purposes, we'll use this texture with 5 columns and 7 rows (right-click and choose Save as…):

Credit: JoesAlotofthings (CC BY 4.0)

To use an animation flipbook, you must create a new CanvasItemMaterial in the Material section of the GPUParticles2D (or CPUParticles2D) node:

Creating a CanvasItemMaterial at the bottom of the particles node inspector

In this CanvasItemMaterial, enable Particle Animation and set H Frames and V Frames to the number of columns and rows present in your flipbook texture:

Configuring the CanvasItemMaterial for the example flipbook texture

Once this is done, the Animation section in ParticleProcessMaterial (for GPUParticles2D) or in the CPUParticles2D inspector will be effective.

Suggerimento

If your flipbook texture has a black background instead of a transparent background, you will also need to set the blend mode to Add instead of Mix for correct display. Alternatively, you can modify the texture to have a transparent background in an image editor. In GIMP, this can be done using the Color > Color to Alpha menu.

Time parameters

Durata di vita

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

Durata di vita: 0.5

Durata di vita: 4.0

Colpo singolo

When enabled, a GPUParticles2D node will emit all of its particles once and then never again.

Preprocesso

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.

Scala di velocità

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.

Esplosività

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: emette particelle a intervalli regolari (valore predefinito).

• 1: emette tutte le particelle simultaneamente.

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

Casualità

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

FPS fisso

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.

Nota

Godot 4.3 does not currently support physics interpolation for 2D particles. As a workaround, disable physics interpolation for the particles node by setting Node > Physics Interpolation > Mode at the bottom of the inspector.

Delta frazionario

Setting Fract Delta to true results in fractional delta calculation, which has a smoother particles display effect. This increased smoothness stems from higher accuracy. The difference is more noticeable in systems with high randomness or fast-moving particles. It helps maintain the visual consistency of the particle system, making sure that each particle's motion aligns with its actual lifespan. Without it, particles might appear to jump or move more than they should in a single frame if they are emitted at a point within the frame. The greater accuracy has a performance tradeoff, particularly in systems with a higher amount of particles.

Parametri di disegno

Rettangolo di visibilità

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 GPUParticles2D 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.

Coordinate locali

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:

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

Ordine di disegno

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.

Particle Process Material Settings

For information on the settings in the ParticleProcessMaterial see this page.