admix / abmix

When you build up a color (or a coordinate) through a big pile of adjustments you can end up writing col = mix(col, target, x) over and over. These helpers do the assignment in place with fewer terms. Reads as one short verb instead of an equation.

// admix: push the FIRST argument toward the second
// x=0 does nothing, x=1 fully replaces a with b
void admix(inout float a, in float b, in float x) { a = mix(a, b, x); }
void admix(inout vec2  a, in vec2  b, in float x) { a = mix(a, b, x); }
void admix(inout vec3  a, in vec3  b, in float x) { a = mix(a, b, x); }
void admix(inout vec4  a, in vec4  b, in float x) { a = mix(a, b, x); }

// abmix: push the SECOND argument toward the first
// x=0 does nothing, x=1 fully replaces b with a
void abmix(in float a, inout float b, in float x) { b = mix(b, a, x); }
void abmix(in vec2  a, inout vec2  b, in float x) { b = mix(b, a, x); }
void abmix(in vec3  a, inout vec3  b, in float x) { b = mix(b, a, x); }
void abmix(in vec4  a, inout vec4  b, in float x) { b = mix(b, a, x); }

admix mutates whichever value is your accumulator; abmix is the mirror image, for when the variable you want to keep is the target rather than the source.

Usage

vec3 col = base;
admix(col, vec3(1.0, 0.3, 0.1), glow);          // warm it up
admix(col, vec3(0.0), vignette);                // darken toward the edges
admix(col, neon, _pulse(uv.x, 0.5, 0.1));       // blend a band in

// abmix keeps `canvas` as the running result while reading a fresh sample
abmix(sample, canvas, feedbackAmount);

Notes

• These are sugar, not magic. They compile to the same mix you’d write by hand. The win is fewer places to misspell the variable when a step gets long.
• Use admix by default; reach for abmix only when flipping the argument order reads more naturally at the call site.