Donut Shader for MagicaVoxel

donut.txt

// Made By @PossiblyAShrub
// Icing Ratio ----------------- controls how much of the donut has icing on it
// Wavy-ness ------------------- controls how wavy the edges of the donut is
// Replace Exisitng Voxels ---- if 0, then the donut SDF brush will replace voxels in it's select area with air

// xs_begin
// author : '@PossiblyAShrub'
// arg : {id = '0' name = 'Icing Ratio' value = '0.4'   range = '0 1'    step = '0.1'    decimal = '2' }
// arg : {id = '1' name = 'Wavy-ness' value = '4'   range = '0 8'    step = '0.5'    decimal = '1' }
// arg : {id = '2' name = 'Replace Existing Voxels' value = '1'   range = '0 1'    step = '1'    decimal = '0' }
// xs_end

//===== user args =====
// uniform float	i_args[8];

//===== built-in args =====
// uniform vec3		i_volume_size;	// volume size [1-256]
// uniform float	i_color_index;	// color index [0-255]
// uniform vec3		i_mirror;		// mirror mode [0,1]
// uniform vec3		i_axis;			// axis mode [0,1]
// uniform float	i_iter;			// iteration index

//===== built-in functions ===== 
// float voxel( vec3 v );			// get voxel color index at position v

// returns rand val between 0 and 1 --- essentialy a hash function
float rand(float seed) { 
	return fract(sin(dot(vec2(seed, -seed), vec2(12.9898, 4.1414))) * 43758.5453);
}

// returns true is voxel should be given the icing color
bool isIcing(vec3 pos, float radius) {
    int squiggleMaskX = floor(sin(pos.x) * i_args[1] + (i_args[0] * radius)) + clamp(rand(length(pos)), 4, 7);
    int squiggleMaskY = floor(sin(pos.y) * i_args[1] + (i_args[0] * radius)) + clamp(rand(length(pos)), 4, 7);
    int squiggleMask = mix(squiggleMaskX, squiggleMaskY, 0.5);

    if (pos.z < radius + 1 && pos.z > radius - squiggleMask) return true;
    return false;
}

// 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) {
	vec3 center = i_volume_size * 0.5;
	vec3 p = ( v - center );
    float radius = i_volume_size * 0.2 + clamp(rand(i_args[2]), -2, 2);

	if( length(vec2(p.z, length(p.xy) - min(center.x,center.y) + radius)) - radius < 0.5) {
        if (isIcing(p, radius)) return i_color_index + 1;
		return i_color_index;
	}
	if (i_args[2] == 0) return 0;
    return voxel(v);
}