#version 450

layout (input_attachment_index = 0, set = 0, binding = 0) uniform subpassInput in_color;

layout(set = 1, binding = 0) uniform sampler3D lut_3d;

layout(location = 0) in vec2 uv;
layout(location = 0) out vec4 out_color;

/* struct wlr_vk_frag_output_pcr_data */
layout(push_constant) uniform UBO {
	layout(offset = 80) float lut_3d_offset;
	float lut_3d_scale;
} data;

layout (constant_id = 0) const int OUTPUT_TRANSFORM = 0;

// Matches enum wlr_vk_output_transform
#define OUTPUT_TRANSFORM_INVERSE_SRGB 0
#define OUTPUT_TRANSFORM_LUT_3D 1

float linear_channel_to_srgb(float x) {
	return max(min(x * 12.92, 0.04045), 1.055 * pow(x, 1. / 2.4) - 0.055);
}

vec4 linear_color_to_srgb(vec4 color) {
	if (color.a == 0) {
		return vec4(0);
	}
	color.rgb /= color.a;
	color.rgb = vec3(
		linear_channel_to_srgb(color.r),
		linear_channel_to_srgb(color.g),
		linear_channel_to_srgb(color.b)
	);
	color.rgb *= color.a;
	return color;
}

void main() {
	vec4 val = subpassLoad(in_color).rgba;
	if (OUTPUT_TRANSFORM == OUTPUT_TRANSFORM_LUT_3D) {
		if (val.a == 0) {
			out_color = vec4(0);
			return;
		}
		// Convert from pre-multiplied alpha to straight alpha
		vec3 rgb = val.rgb / val.a;

		// Apply 3D LUT
		vec3 pos = data.lut_3d_offset + rgb * data.lut_3d_scale;
		rgb = texture(lut_3d, pos).rgb;

		// Back to pre-multiplied alpha
		out_color = vec4(rgb * val.a, val.a);
	} else { // OUTPUT_TRANSFORM_INVERSE_SRGB
		// Produce post-premultiplied sRGB encoded values
		out_color = linear_color_to_srgb(val);
	}
}