const float pureWhite = 1.0;

vec3 reinhard(vec3 x)
{
//	return x / (x + vec3(1.0));

	// Reinhard tonemapping operator.
	// see: "Photographic Tone Reproduction for Digital Images", eq. 4
	float luminance = dot(x, vec3(0.2126, 0.7152, 0.0722));
	float mappedLuminance = (luminance * (1.0 + luminance/(pureWhite*pureWhite))) / (1.0 + luminance);
	// Scale color by ratio of average luminances.
	return (mappedLuminance / luminance) * x;
}

// https://knarkowicz.wordpress.com/2016/01/06/aces-filmic-tone-mapping-curve/
vec3 ACESFilm(vec3 x)
{
    float a = 2.51f;
    float b = 0.03f;
    float c = 2.43f;
    float d = 0.59f;
    float e = 0.14f;
    return (x*(a*x+b))/(x*(c*x+d)+e);
}

// https://www.slideshare.net/ozlael/hable-john-uncharted2-hdr-lighting
vec3 filmicF(vec3 x)
{
	float A = 0.22f;
	float B = 0.30f;
	float C = 0.10f;
	float D = 0.20f;
	float E = 0.01f;
	float F = 0.30f;
	return ((x*(A*x+C*B)+D*E)/(x*(A*x+B)+D*F)) - E/F;
}

vec3 filmic(vec3 x)
{
	return filmicF(x) / filmicF(vec3(11.2f));
}

vec4 tonemap(vec4 x)
{
	// Use ACES Filmic by default. Reinhard above kept for reference, but
	// with pureWhite=1.0 it collapses to identity (L*(1+L)/(1+L) = L) and
	// just clips HDR>1.0 at the framebuffer -> washed-out / burnt look.
	// ACES gives a smooth highlight shoulder + slight toe contrast.

	// Last-line-of-defense sanitize. ACESFilm has the form
	//   (x*(a*x+b)) / (x*(c*x+d)+e)
	// which maps NaN -> NaN and +Inf -> NaN (Inf/Inf). Either turns the
	// pixel black after framebuffer clamp. A negative HDR input feeds a
	// negative numerator/denominator and can produce non-physical output
	// that also looks like a black flash. Clamp to a sensible range
	// before the curve so a single bad upstream pixel can't escape.
	vec3 hdr = x.rgb;
	hdr = mix(hdr, vec3(0.0), vec3(any(isnan(hdr)) || any(isinf(hdr))));
	hdr = max(hdr, vec3(0.0));
	return FBOUT(vec4(ACESFilm(hdr), x.a));
	//return FBOUT(vec4(reinhard(x.rgb), x.a));
}