// Copyright (c) 2023 Lachlan McDonald
// This work is licensed under the MIT License (MIT)
// https://github.com/lachlanmcdonald/magicavoxel-shaders
//
// This script utilises or modifies code from other projects or publications.
// Please see the attributions below for more information:
//
// 1. Copyright (c) 2015 Michael Feldstein <https://github.com/msfeldstein/glsl-map>
//    MIT License (MIT)
//    https://github.com/msfeldstein/glsl-map/blob/master/LICENSE.md
//
// xs heightmap [Blur] [Auto Balance] [Reverse]
//
// xs_begin
// author : '@lachlanmcdonald'
// arg : { name = 'Blur'  var = 'm_blur'  range = '0 10'  value = '0'  step = '1'  precision = '0' }
// arg : { name = 'Auto Balance'  var = 'm_auto'  range = '0 1'  value = '1'  step = '1'  precision = '0' }
// arg : { name = 'Reverse'  var = 'm_reverse'  range = '0 1'  value = '0'  step = '1'  precision = '0' }
// xs_end

float blur = float(m_blur);
bool auto_balance = m_auto > 0.0;
bool reverse = m_reverse > 0.0;

float luminance(vec3 c) {
	return dot(c, vec3(0.2125, 0.7154, 0.0721));
}

float range(float value, float inMin, float inMax, float outMin, float outMax) {
	return outMin + (outMax - outMin) * (value - inMin) / (inMax - inMin);
}

float map(vec3 v) {
	vec3 uv = floor(v) / i_volume_size;
	float i = voxel(floor(vec3(v.xy, 0.5)));
	float l = luminance(palette(i).rgb);

	if (blur > 0.0) {
		float c = 1.0;

		for (float x = max(0.0, v.x - blur), xm = min(i_volume_size.x, v.x + blur); x <= xm; x += 1.0) {
			for (float y = max(0.0, v.y - blur), ym = min(i_volume_size.y, v.y + blur); y <= ym; y += 1.0) {
				vec3 p = vec3(x, y, 0.0);

				if (all(equal(v, p)) == false) {
					float j = voxel(p);
					l += luminance(palette(j).rgb);
					c += 1.0;
				}
			}
		}

		l /= c;
	}

	if (float(i_num_color_sels) > 1.0 && auto_balance) {
		float lower = 1.0;
		float upper = 0.0;

		for (int i = 0; i < i_num_color_sels; i += 1) {
			vec4 c = palette(color_sel(float(i)));
			float v = luminance(c.rgb);
			lower = min(lower, v);
			upper = max(upper, v);
		}

		l = range(l, lower, upper, 0.0, 1.0);
	}

	if (reverse) {
		l = 1.0 - l;
	}

	l = ceil(l * i_volume_size.z) / i_volume_size.z;
	return l < uv.z ? 0.0 : i;
}