One of the great advantages of Core Image Kernel Language being such a close relative of GLSL is that I can scour through sites such as Shadertoy and GLSL Sandbox and copy some of the amazing work produced by their contributors pretty much verbatim to create new Core Image filters. Two such examples my CausticNoise (based on this Shadertoy project) and VoronoiNoise (based on this GLSL Sandbox project) filters. Both of these generator filters have now been included in Filterpedia and can be used like any other Core Image filter.
Caustic Noise
Caustic Noise generates a tileable and animatable noise reminiscent of the caustic patterns you may be at the bottom of a swimming pool. On its own, it creates a nice effect, however, I've chained together with my height field refraction kernel that powers my RefractedTextFilter, to create a CausticRefraction filter:
Since the filter is animatable by its inputTime attribute, it works very nicely with live video. My NemoCam project applies caustic refraction to a live video feed from an iOS device to give a wobbly, underwater effect:
Voronoi Noise
Voronoi noise (also known as Worley or cellular noise) is created by setting the color of each pixel based on its distance to the nearest randomly distributed point. This filter is also animatable (as you can see above) by incrementing its inputSeed attribute. Using my normal map filter, both of these noise generators make excellent sources for normal maps for SceneKit materials:
Core Image for Swift
If you'd like to learn more about the power of Core Image for generating textures, including how to leverage Metal compute shaders to create other types of noise, may I recommend my book, Core Image for Swift. Core Image for Swift is available from both Apple's iBooks Store or, as a PDF, from Gumroad. IMHO, the iBooks version is better, especially as it contains video assets which the PDF version doesn't.
It's been a fairly busy few months at my "proper" job, so my recreational Houdini tinkering has taken a bit of a back seat. However, when I saw my Swarm Chemistry hero, Hiroki Sayama tweeting a link to How a life-like system emerges from a simple particle motion law, I thought I'd dust off Houdini to see if I could implement this model in VEX. The paper discusses a simple particle system, named Primordial Particle Systems (PPS), that leads to life-like structures through morphogenesis. Each particle in the system is defined by its position and heading and, with each step in the simulation, alters its heading based on the PPS rule and moves forward at a defined speed. The heading is updated based on the number of neighbors to the particle's left and right. The project set up is super simple:
Inside a geometry node, I create a grid, and randomly scatter 19,000 points across it. An attribute wrangle node assigns a random value to @angle:
@angle = $PI * 2 * rand(@ptnum);
The real magic happens inside another attribute wrangle inside the solver. In a nutshell, my VEX code iterates over each point's neighbors and sums the neighbor count to its left and right. To figure out the chirality, I use some simple trigonometry to rotate the vector defined by the current particle and the neighbor by the current particle's angle, then calculate the angle of the rotated vector.
Not quite finally, because to make things pretty, I update the color using the number of neighbors to control hue:
@Cd = hsvtorgb(N / maxParticles, 1.0, 1.0);
Easy! Solitons Emerging from Tweaked Model
I couldn't help tinkering with the published PPS math by making the speed a function of the number of local neighbors:
@speed = 1.5 * (N / maxParticles);
In the video above, alpha is 182° and beta is -13°. References Schmickl, T. et al. How a life-like system emerges from a simple particle motion law. Sci. Rep.6, 37969; doi: 10.1038/srep37969 (2016).
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