// xs_begin
// src : 'https://www.iquilezles.org/www/articles/distfunctions/distfunctions.htm'
// arg : { var = 'm_radius' name = 'Radius' value = '5'   range = '0 64'    step = '0.1'    precision = '1' }
// xs_end

//===== built-in args =====
// uniform vec3		i_volume_size;		// volume size [1-256]
// uniform float	i_color_index;		// current color index [0-255]
// uniform int		i_num_color_sels;	// number of color selections [1-255]

//===== built-in functions ===== 
// float voxel( vec3 v );				// get voxel color index
// float color_sel( float k );			// get kth selected color index
// vec4 palette( float index );			// get palette color

// generate a new voxel color index [0, 255] at position v ( v is at the center of voxel, such as vec3( 1.5, 2.5, 4.5 ) )
float map( vec3 v ) {
	v -= i_volume_size * 0.5;
	vec3 q = abs(v) - i_volume_size * 0.5 + m_radius;
	if ( length(max(q,0.0)) + min(max(q.x,max(q.y,q.z)),0.0) < m_radius ) {
		return i_color_index;
	}
	return 0.0;
}