#[set(everything)]
const constants: {
	screen_size_inv: float2;
	current_mip_level: int;
};

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

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

struct vert_in {
	pos: float2;
}

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

const bloom_knee: float = 0.5;
const bloom_threshold: float = 0.8;
const epsilon: float = 0.000062;

fun bloom_downsample_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 downsample_dual_filter(tex: tex2d, tex_coord: float2, texel_size: float2): float3 {
	var delta: float3 = float3(texel_size.xy, texel_size.x) * float3(0.5, 0.5, -0.5);

	var result: float3;
	result  = sample_lod(tex, tex_sampler, tex_coord,            0.0).rgb * 4.0;
	result += sample_lod(tex, tex_sampler, tex_coord - delta.xy, 0.0).rgb;
	result += sample_lod(tex, tex_sampler, tex_coord - delta.zy, 0.0).rgb;
	result += sample_lod(tex, tex_sampler, tex_coord + delta.zy, 0.0).rgb;
	result += sample_lod(tex, tex_sampler, tex_coord + delta.xy, 0.0).rgb;

	return result * (1.0 / 8.0);
}

fun bloom_downsample_pass_frag(input: vert_out): float4 {
	var color: float4;
	color.rgb = downsample_dual_filter(tex, input.tex, constants.screen_size_inv);

	if (constants.current_mip_level == 0) {
		var brightness: float = max(color.r, max(color.g, color.b));

		var softening_curve: float = brightness - bloom_threshold + bloom_knee;
		softening_curve = clamp(softening_curve, 0.0, 2.0 * bloom_knee);
		softening_curve = softening_curve * softening_curve / (4 * bloom_knee + epsilon);

		var contribution_factor: float = max(softening_curve, brightness - bloom_threshold);

		contribution_factor /= max(epsilon, brightness);

		color.rgb *= contribution_factor;
	}

	color.a = 1.0;
	return color;
}

#[pipe]
struct pipe {
	vertex = bloom_downsample_pass_vert;
	fragment = bloom_downsample_pass_frag;
}