sorting triplets of floats in a buffer (vertices, indices, normals etc. ) using the QuickSort method.

float triplets sorting method

/*
the quick sort method is described here :
http://antjanus.com/blog/web-development-tutorials/understanding-quicksort-js-native-implementation/
*/


function tripletSort( arr )
{

    if (arr.length === 0)return [];

    var left = [];
    var right = [];

    var p0 = arr[0], p1 = arr[1], p2 = arr[2];

    var v0, v1, v2;
    for (var i = 3; i < arr.length; i+=3 )
    {

        v0 = arr[i];
        v1 = arr[i+1];
        v2 = arr[i+2];

        if( v0 <= p0
                &&  v1 <= p1
                &&  v2 <= p2 )
        {
            left.push( v0, v1, v2 );
        }
        else
        {
            right.push( v0, v1, v2 );
        }

    }
    return tripletSort( left ).concat( p0, p1, p2, tripletSort( right ) );
}
/////////////////////////////////////////////

// + custom sort method

/////////////////////////////////////////////

function distance( a,b,c, d,e,f )
{
    var d0 =  a - d;
    var d1 =  b - e;
    var d2 =  c - f;
    return d0*d0 + d1*d1 + d2*d2;
}

function distanceSort( arr, point, method )
{

    if (arr.length === 0)return [];

    var left = [];
    var right = [];

    var p0 = arr[0], p1 = arr[1], p2 = arr[2];

    var pivot = method(    point[ 0 ], point[ 1 ], point[ 2 ], p0, p1, p2 );

    var v0, v1, v2;
    for (var i = 3; i < arr.length; i+=3 )
    {

        v0 = arr[i];
        v1 = arr[i+1];
        v2 = arr[i+2];

        if( method(    point[ 0 ], point[ 1 ], point[ 2 ], v0, v1, v2 ) < pivot )
        {
            left.push( v0, v1, v2 );
        }
        else
        {
            right.push( v0, v1, v2 );
        }

    }
    return distanceSort( left, point, method ).concat( p0, p1, p2, distanceSort( right, point, method ) );
}


///////////////////////////////////////////

//  test

///////////////////////////////////////////

var a = [
    4,40,4,
    -2,2,2,
    0,100,0,
    1,10,-1,
    -7,30,3
];

console.log( "unsorted array:\n", a );

console.log( "--------------- \ntripletSort :" );
console.log( tripletSort( a ) );

var p = [ 0,0,0 ];
console.log( "--------------- \ndistanceSort fomr point P:", p );
console.log( distanceSort( a, p, distance ) );

p = [45,45,45];
console.log( "--------------- \ndistanceSort fomr point P:", p );
console.log( distanceSort( a, p, distance ) );


/*
expected result:

unsorted array:
[4, 40, 4, -2, 2, 2, 0, 100, 0, 1, 10, -1, -7, 30, 3]
---------------
tripletSort : 
[-2, 2, 2, 1, 10, -1, -7, 30, 3, 4, 40, 4, 0, 100, 0]
---------------
distanceSort fomr point P: [0, 0, 0]
[-2, 2, 2, 1, 10, -1, -7, 30, 3, 4, 40, 4, 0, 100, 0]
---------------
distanceSort fomr point P: [45, 45, 45]
[4, 40, 4, -7, 30, 3, 1, 10, -1, -2, 2, 2, 0, 100, 0]
*/