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#include "tone_iq.cginc"
#ifndef __TONE_INC
#define __TONE_INC
// This library contains a bunch of useful tonemapping curves.
// https://knarkowicz.wordpress.com/2016/01/06/aces-filmic-tone-mapping-curve/
// cc0
float3 aces_filmic(float3 x) {
float a = 2.51f;
float b = 0.03f;
float c = 2.43f;
float d = 0.59f;
float e = 0.14f;
return saturate((x*(a*x+b))/(x*(c*x+d)+e));
}
// Clamp x to [0, k].
// Assumes that x is already on [0, 1].
// Nice properties:
// 1. At x=0, the derivative is 1.
// 2. No transcendental ops, and branchless.
// This original attempt at a smooth minimum function has a problem:
// f(x, k) = k * x / (x + k)
// As k -> inf, f(x, k) -> 1. We want f(x, k) -> k.
// Claude suggests this:
// f(x, a, j) = j * (1 + a) * x / (1 + ax)
// At x=1:
// f(1, a, j) = j * (1 + a) / (1 + a)
// = j
// At infinity, we know that:
// b * x / (x + b) -> 1
// So:
// f(x, a, j) = j * (1 + a) * x / (1 + ax)
// = (j + ja) * x / (1 + ax)
// = (jx + jax) / (1 + ax)
// = jx / (1 + ax) + jax / (1 + ax)
// = j (x / (1 + ax) + ax / (1 + ax))
// At infinity, this becomes:
// j (1/a + 1)
// So if we want the limit to be k:
// k = j (1/a + 1)
// k/j = 1/a + 1
// k/j - 1 = 1/a
// a = 1 / (k/j - 1)
// Smooth, analytic min function.
// Guarantees that x <= k for all positive x. At x=1, returns j.
// Caller must ensure that j < k.
float smooth_min(float x, float j, float k) {
float a = 1 / (k / j - 1);
return j * (1 + a) * x / (1 + a * x);
}
float3 smooth_min(float3 x, float j, float k) {
float a = 1 / (k / j - 1);
return j * (1 + a) * x / (1 + a * x);
}
float smooth_clamp(float x, float lo, float hi) {
return smooth_max(smooth_min(x, (lo + (hi - lo)/2), hi), lo);
}
#endif // __TONE_INC
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