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2.3.7 Particles

Effects like smoke, fire, sparks, etc. are often achieved by animating lots of little, short-lived sprites known as “particles”. In fact, all of these effects, and more, can be accomplished by turning a few configuration knobs in a “particle system”. A particle system takes care of managing the many miniscule moving morsels so the developer can quickly produce an effect and move on with their life. The (chickadee graphics particles) module provides an API for manipulating particle systems.

Below is an example of a very simple particle system that utilizes nearly all of the default configuration settings:

(use-modules (chickadee graphics particles))
(define texture (load-image "particle.png"))
(define particles (make-particles 2000 #:texture texture))

In order to put particles into a particle system, a particle “emitter” is needed. Emitters know where to spawn new particles, how many of them to spawn, and for how long they should do it.

Below is an example of an emitter that spawns 16 particles per frame at the coordinates (320, 240):

(use-modules (chickadee math vector))
(define emitter (make-particle-emitter (vec2 320.0 240.0) 16))
(add-particle-emitter particles emitter)

To see all of the tweakable knobs and switches, read on!

Procedure: make-particles capacity [#:blend-mode alpha] [#:color white] [#:end-color transparent] [#:texture] [#:animation-rows 1] [#:animation-columns 1] [#:width] [#:height] [#:speed-range (vec2 0.1 1.0)] [#:acceleration-range (vec2 0.0 0.1)] [#:direction-range (vec2 0 (* 2 pi))] [#:lifetime 30] [#:sort]

Return a new particle system that may contain up to capacity particles. Achieving the desired particle effect involves tweaking the following keyword arguments as needed:

- blend-mode: Pixel blending mode. alpha by default. (see Blending for more about blend modes).

- start-color: The tint color of the particle at the beginning of its life. White by default.

- end-color: The tint color of the particle at the end of of its life. Completely transparent by default for a fade-out effect. The color in the middle of a particle’s life will be an interpolation of start-color and end-color.

- texture: The texture applied to the particles. The texture may be subdivided into many animation frames.

- animation-rows: How many animation frame rows there are in the texture. Default is 1.

- animation-columns: How many animation frame columns there are in the texture. Default is 1.

- width: The width of each particle. By default, the width of an animation frame (in pixels) is used.

- height: The height of each particle. By default, the height of an animation frame (in pixels) is used.

- speed-range: A 2D vector containing the min and max particle speed. Each particle will have a speed chosen at random from this range. By default, speed ranges from 0.1 to 1.0.

- acceleration-range: A 2D vector containing the min and max particle acceleration. Each particle will have an acceleration chosen at random from this range. By default, acceleration ranges from 0.0 to 0.1.

- direction-range: A 2D vector containing the min and max particle direction as an angle in radians. Each particle will have a direction chosen at random from this range. By default, the range covers all possible angles.

- lifetime: How long each particle lives, measured in updates. 30 by default.

- sort: youngest if youngest particle should be drawn last or oldest for the reverse. By default, no sorting is applied at all.

Procedure: particles? obj

Return #t if obj is a particle system.

Procedure: update-particles particles

Advance the simulation of particles.

Procedure: draw-particles particles

Render particles.

Procedure: draw-particles* particles matrix

Render particles with matrix applied.

Procedure: make-particle-emitter spawn-area rate [duration]

Return a new particle emitter that spawns rate particles per frame within spawn-area (a rectangle or 2D vector) for duration frames. If duration is not specified, the emitter will spawn particles indefinitely.

Procedure: particle-emitter? obj

Return #t if obj is a particle emitter.

Procedure: particle-emitter-spawn-area emitter

Return the spawn area for emitter.

Procedure: particle-emitter-rate emitter

Return the number of particles that emitter will spawn per frame.

Procedure: particle-emitter-life emitter

Return the number of frames remaining in emitter’s lifespan.

Procedure: particle-emitter-done? emitter

Return #t if emitter has finished spawning particlces.

Procedure: add-particle-emitter particles emitter

Add emitter to particles.

Procedure: remove-particle-emitter particles emitter

Remove emitter to particles


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