Alpha blend pixel colors

AlphaBlend.hx

    public inline
    function channelBlend( ch0: PixelChannel
                         , ch1: PixelChannel
                         , ch2: PixelChannel
                         , ch3: PixelChannel ){
        var a1: Float = c0; // abstract conversion
        var r1: Float = c1;
        var g1: Float = c2;
        var b1: Float = c3;
        var a2: Float = ch0;
        var r2: Float = ch1;
        var g2: Float = ch2;
        var b2: Float = ch3;
        var a3 = a1 * ( 1 - a2 );
        var r = colBlendFunc( r1, r2, a3, a2 );
        var g = colBlendFunc( g1, g2, a3, a2 );
        var b = colBlendFunc( b1, b2, a3, a2 );
        var a = alphaBlendFunc( a3, a2 );
        return fromChannels( a, r, g, b );
    }
    inline function colBlendFunc( x1: Float, x2: Float, a3: Float, a2: Float ): Int
    return Std.int( 255 * ( x1 * a3 + x2 * a2 ) );
inline function alphaBlendFunc( a3: Float, a2: Float ): Int
    return Std.int( 255 * ( a3 + a2 ) );
    /*inline
    public static function fromChannels( ch0: Int, ch1: Int, ch2: Int, ch3: Int ): Pixel32
        return ( cast ch0 << 24 | ch1 << 16 | ch2 << 8 | ch3 : Pixel32 );*/
inline function fromChannels( ch0: Int, ch1: Int, ch2: Int, ch3: Int ): Int
          return ch0 << 24 | ch1 << 16 | ch2 << 8 | ch3;
@:forward
@:transient
abstract PixelChannel( Int ) to Int from Int {
    inline
    public function new( v: Int )
        this = v;
    @:from
    public inline static function toHexInt( c: Float ): PixelChannel
        return ( cast Math.round( c * 255 ) : PixelChannel );
    @:to
    public inline function colIntToFloat(): Float
        return ( this == 0 )? 0.: this/255;
    @:to
    public inline function stringHash(): String 
        return '#' + StringTools.hex( this, 2 );
    inline
    public static function boundChannel( f: Float ): Int {
        var i = Std.int( f );
        if( i > 0xFF ) i = 0xFF;
        if( i < 0 ) i = 0;
        return new PixelChannel( i );
    }
}