Wrote a full-length devlog about a core feature of Kolori and its implementation, but it got deleted for being “too long”. Lets try again then, with a piece that only demands a bit of your time.

Kolori offers users three (at the moment) coloring modes: HSL, HSLuv, and custom palette generation. How do these work?

Custom palette generation

Unlike HSL and HSLuv, using a custom palette to color the complex plane is much more simple. Kolori lets the user input four arbitrary RGB colors. We then use Inigo Quilez’s cosine-based formula for procedural palette
generation to determine the color of a pixel. An article of his that describes it is here: https://iquilezles.org/articles/palettes/.

The shader code that does it all:

// From https://iquilezles.org/articles/palettes/
vec4 palette(float t, vec3 a, vec3 b, vec3 c, vec3 d)
{
	return vec4(a + b*cos(TAU * (c*t+d)), 1);
}

Our a, b, c, and d are the colors the user has selected, and t is an input variable to vary. However, one would notice that t is a scalar, while we work in the complex numbers. How would we map the plane onto the real line in order to get a valid t to input into palette? The answer we chose is simple: we take the projection onto the real axis–i.e. just taking the real part of the complex number This is an answer that a user would expect and is pointed out in the user guide. Furthermore, by not choosing ahead of time for the user, we allow the user to exert more control over what they wish to generate.