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#ifdef USE_ALPHA_HASH
/* From the paper "Hashed Alpha Testing" by Chris Wyman and Morgan McGuire */
float hash(vec2 a)
{
return fract(1e4 * sin(17.0 * a.x + 0.1 * a.y) * (0.1 + abs(sin(13.0 * a.y + a.x))));
}
float hash3d(vec3 a)
{
return hash(vec2(hash(a.xy), a.z));
}
float hashed_alpha_threshold(vec3 co)
{
/* Find the discretized derivatives of our coordinates. */
float max_deriv = max(length(dFdx(co)), length(dFdy(co)));
float pix_scale = 1.0 / (alphaHashScale * max_deriv);
/* Find two nearest log-discretized noise scales. */
float pix_scale_log = log2(pix_scale);
vec2 pix_scales;
pix_scales.x = exp2(floor(pix_scale_log));
pix_scales.y = exp2(ceil(pix_scale_log));
/* Compute alpha thresholds at our two noise scales. */
vec2 alpha;
alpha.x = hash3d(floor(pix_scales.x * co));
alpha.y = hash3d(floor(pix_scales.y * co));
/* Factor to interpolate lerp with. */
float fac = fract(log2(pix_scale));
/* Interpolate alpha threshold from noise at two scales. */
float x = mix(alpha.x, alpha.y, fac);
/* Pass into CDF to compute uniformly distrib threshold. */
float a = min(fac, 1.0 - fac);
float one_a = 1.0 - a;
float denom = 1.0 / (2 * a * one_a);
float one_x = (1 - x);
vec3 cases = vec3((x * x) * denom, (x - 0.5 * a) / one_a, 1.0 - (one_x * one_x * denom));
/* Find our final, uniformly distributed alpha threshold. */
float threshold = (x < one_a) ? ((x < a) ? cases.x : cases.y) : cases.z;
/* Jitter the threshold for TAA accumulation. */
threshold = fract(threshold + alphaHashOffset);
/* Avoids threshold == 0. */
threshold = clamp(threshold, 1.0e-6, 1.0);
return threshold;
}
#endif
#define NODETREE_EXEC
void main()
{
#if defined(USE_ALPHA_HASH)
Closure cl = nodetree_exec();
float opacity = saturate(1.0 - avg(cl.transmittance));
# if defined(USE_ALPHA_HASH)
/* Hashed Alpha Testing */
if (opacity < hashed_alpha_threshold(worldPosition)) {
discard;
}
# endif
#endif
}
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