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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))
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)
To see all of the tweakable knobs and switches, read on!
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.
Return #t if obj is a particle system.
Advance the simulation of particles.
Render particles.
Render particles with matrix applied.
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.
Return #t if obj is a particle emitter.
Return the spawn area for emitter.
Return the number of particles that emitter will spawn per frame.
Return the number of frames remaining in emitter’s lifespan.
Return #t if emitter has finished spawning particlces.
Add emitter to particles.
Remove emitter from particles
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