// 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
//
// 2. Copyright (c) 2020 ValgoBoi <https://github.com/ValgoBoi/clover-noise>
//    MIT License (MIT)
//    https://github.com/ValgoBoi/clover-noise/blob/master/LICENSE
//
// xs grass_fit [Mode] [Density] [Height] [Seed]
//
// xs_begin
// author : '@lmcdx.bsky.social'
// arg : { name = 'Mode'  var = 'm_mode'  range = '0 4'  value = '0'  step = '1'  precision = '0' }
// arg : { name = 'Density'  var = 'm_density'  range = '1 256'  value = '2'  step = '1'  precision = '0' }
// arg : { name = 'Height'  var = 'm_strand_height'  range = '1 256'  value = '10'  step = '1'  precision = '0' }
// arg : { name = 'Seed'  var = 'global_seed'  range = '1 100'  value = '1'  step = '1'  precision = '0' }
// xs_end

int mode = int(m_mode);
float density = m_density;

float hash(vec2 p, float seed) {
	p += seed + global_seed;
	return fract(1e4 * sin(17.0 * p.x + p.y * 0.1) * (0.1 + abs(sin(p.y * 13.0 + p.x))));
}

float hash(vec2 p) {
	return hash(p, 0.0);
}

float pal(float p) {
	float f = floor(mix(0.0, float(i_num_color_sels), p));
	return color_sel(f);
}

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

bool isSelectedColor(float p) {
	for (int i = 0; i < i_num_color_sels; i += 1) {
		if (p == color_sel(float(i))) {
			return true;
		}
	}
	return false;
}

float map(vec3 v) {
	v = floor(v);
	vec2 cell = floor(vec2(v.xy) / density);
	vec3 local = floor(mod(v, density));
	vec2 placement = floor(vec2(hash(cell.xy), hash(cell.xy, 170.3170)) * density);

	float base_height = -1.0;
	bool is_gap = false;

	for (float z = 0.0; z <= v.z; z += 1.0) {
		vec3 p = floor(vec3(v.xy, z));
		float i = voxel(p);

		if (i == 0.0 || isSelectedColor(i)) {
			if (is_gap == false) {
				base_height = z;
				is_gap = true;
			}
		} else {
			is_gap = false;
		}
	}

	if (base_height > -1.0) {
		if (all(equal(local.xy, placement))) {
			float d = hash(cell.yx, -170.3170);
			float h = m_strand_height * d;

			if (v.z >= base_height && v.z <= h + base_height) {
				float f;

				if (mode == 0) {
					f = d;
				} else if (mode == 1) {
					f = hash(vec2(v.z, h));
				} else if (mode == 2) {
					f = hash(v.xy);
				} else if (mode == 3) {
					f = range(v.z, base_height, h + base_height, 0.0, 1.0);
				} else if (mode == 4) {
					f = range(v.z, base_height, h + base_height, 1.0, 0.0);
				}

				return pal(f);
			}
		}
	}

	return voxel(v);
}