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Smooth minimum functions for GLSL, sourced from Iñigo Quílez's article.

Particularly useful when doing Shadertoy-style raymarching with distance fields: you can smoothly blend between two volumes, instead of doing a hard union with min(a, b).

Check it out in action



smin(float a, float b, float k)

Blends smoothly between a and b, with a smoothing amount determined by the value of k. For example:

#pragma glslify: smin require(glsl-smooth-min) 
float doModel(vec3 position) {
  // Take two sphere volumes 
  float a = length(position + 0.5) - 0.7;
  float b = length(position - 0.5) - 0.7;
  // And smooth them together 
  return smin(a, b, 0.8);

There are three variants of this function available, all with the same function signature:

#pragma glslify: poly require(glsl-smooth-min/poly) 
#pragma glslify: pow require(glsl-smooth-min/pow) 
#pragma glslify: exp require(glsl-smooth-min/exp) 
// Exports `poly` by default 
#pragma glslify: poly require(glsl-smooth-min) 

Each of these variants differ somewhat in their results, and some are more appropriate in specific situations:

These three functions produce smooth results, with different qualities. The three accept a paramter k that controls the radious/distance of the smoothness. From these three, probably the polynomial is the fastest, and also the easiest to control, for k maps directly to a blending band size/distance. Unlike the other two, it probably suffers from second order discontinuities (derivatives), but visually is pleasing enough for most applications.


See stackgl/contributing for details.


MIT. See for details.