#[set(everything)]
const constants: {
	empty: float4;
};

#[set(everything)]
const sampler_linear: sampler;

#[set(everything)]
const tex: tex2d;

struct vert_in {
	pos: float2;
}

struct vert_out {
	pos: float4;
	tex: float2;
}

const auto_exposure_speed: float = 1.0;

fun histogram_pass_vert(input: vert_in): vert_out {
	var output: vert_out;
	output.tex = input.pos.xy * 0.5 + 0.5;
	output.tex.y = 1.0 - output.tex.y;
	output.pos = float4(input.pos.xy, 0.0, 1.0);
	return output;
}

fun histogram_pass_frag(input: vert_out): float4 {
	var color: float4;
	color.a = 0.01 * auto_exposure_speed;
	color.rgb = sample_lod(tex, sampler_linear, float2(0.5, 0.5), 0.0).rgb +
				sample_lod(tex, sampler_linear, float2(0.2, 0.2), 0.0).rgb +
				sample_lod(tex, sampler_linear, float2(0.8, 0.2), 0.0).rgb +
				sample_lod(tex, sampler_linear, float2(0.2, 0.8), 0.0).rgb +
				sample_lod(tex, sampler_linear, float2(0.8, 0.8), 0.0).rgb;
	color.rgb = color.rgb / 5.0;
	return color;
}

#[pipe]
struct pipe {
	vertex = histogram_pass_vert;
	fragment = histogram_pass_frag;
}