Particles (The Chickadee Game Toolkit)

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5.3.6 Particles

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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))
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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 rect))
-(define emitter (make-particle-emitter (make-rect 0.0 0.0 320.0 240.0) 16))
-(add-particle-emitter particles emitter)
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To see all of the tweakable knobs and switches, read on! -

Procedure: make-particles capacity [#:blend-mode] [#: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 blending is used by -default. (see Render Settings 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. -

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Procedure: particles? obj: Return #t if obj is a particle system. -

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Procedure: update-particles particles: Advance the simulation of particles. -

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Procedure: draw-particles particles: Render particles. -

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Procedure: draw-particles* particles matrix: Render particles with matrix applied. -

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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. -

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Procedure: particle-emitter? obj: Return #t if obj is a particle emitter. -

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Procedure: particle-emitter-spawn-area emitter: Return the spawn area for emitter. -

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Procedure: particle-emitter-rate emitter: Return the number of particles that emitter will spawn per -frame. -

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Procedure: particle-emitter-life emitter: Return the number of frames remaining in emitter’s lifespan. -

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Procedure: particle-emitter-done? emitter: Return #t if emitter has finished spawning particlces. -

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Procedure: add-particle-emitter particles emitter: Add emitter to particles. -

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Procedure: remove-particle-emitter particles emitter: Remove emitter from particles -

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